Edit:
I think I'm attempting to charge the system too quickly. I assume I should go ahead and force the compressor to turn on to help build the pressure up quicker.
How is the high pressure and low connected? Would pulling vacuum on the low pressure side cause vacuum on the high or does the compressor and orifice hose keep the two sides completely separate? I think I need to re-pull vacuum on both sides and recharge at 35psi low pressure again.
Also the system's oil is supposed to stay in the system after pulling vacuum, correct? I should probably add like 1-2oz if it hasn't been drained out?
Not 100% on the question in there but here goes. What is going on? You charged the system but the compressor not coming on? Yes vac'ing down the low side does the compressor and high side. It is to suck stuff out but also check to see if it holds that vacuum for 30min to and hour to double check for leaks. Yes some oil will stay in there best to keep track of how much comes out if you can. Then charge it up. But if you have already charged it. Take a pressure reading on both the low and the high side. Find out if you have the right pressures or no pressure on the high side. If you have the right pressure or close I would jump the pressure switch and see if it gets cold. If you don't have pressure or real close to the right pressure on the high side. Something is wrong and plugged up in there. Did you install a new orifice tube? If not and you have the factory hoses you have to cut the metal tube and install a new section with new orifice tube. Most auto parts stores can get you a kit for this. Also if your installing R134 and gonna replace the orifice tube get the auto adjustable model. It will adjust to what the motor is doing to make the motor work best at idle and higher rpm's. I didn't do this and at idle at a stop light it starts to get warmer quickly. I'm told part is due to the orifice tube and part due to the r12 condenser not having near the fin count as the R134 style. So install a newer R134 style condenser or mount a large electric fan on the front of the R12 unit that you can turn on in town.
hope this helps
Stuckman
My system was taken apart and capped off when we had to do the heatercore last year, being reconnected after the swap was done hours later. It's been dry since but not much oil came out with the rest of the system when this was done.
New lines, compressor, orifice rube, and acspoogeulator were installed 2-3 years ago, and condenser/evaporator cleaned out, after being a/c-less for 10+ years. The swap was done with conversion parts and fresh oil. The system ran good at that point in time and is still leak free. I'm just not sure if me only pulling vacuum on the low side earlier also did the high side. If not, I have to redo it, otherwise I just need to continue where I had to leave off today due to it getting dark.
I'm just looking to get the a/c back up and running. With my vacuum pump, I've got that parts set , along with all the gauges and such, I just need to know if pulling vacuum on the low side created vacuum on the high and get an idea on how much oil I should add back in. The latter may not be something I can get from you guys. I would think that without vacuum though, the oil would also come out but I get nothing but air coming out of it.
Your lack of oil coming out during the vac'ing process isn't nothing major. That oil likes to stay in the compressor. To get it out you would need to take it off and drain it. Then if no oil came out then you need to put little if any in there. And yes when you pull vacuum on the low side it does both sides and the compressor.
this question bugged me a few years ago and so i made a few observations and asked a few questions.
the correct answer to how much oil will be "refer to the maker of your compressor",,yeah right.
Most any real good compressor has a sight glass on the side. our compressors sit sideways and any good compressor I have seen on larger diesel engines and such have a sight glass. Its location is approx 1/4 to 1/3 of the way up from the bottom. The sight glass should show the oil pretty much dead middle.
I looked at many good compressors of various sizes and noticed the sight glass is oriented at the same location.
My conclusion what that you fill the compressor about 1/3 of teh way full. when the pump kicks on, the oil level will drop because a lot of it will coat all your interior lines. The length of the line on some applications could be as much as 60 loop feet.
there is a pretty good bit of math involved when compensating for line lenght. ours are probably only 10loop feet so that would be the amount of line that gets coated.
Too much oil and your compressor locks up because the oil expands, too little and it does not lubricate.
I asked many good hvac guys this one question and most of them pretty much agreed.> " in general, isnt it true that a typical compressor needs to be about 1/4 - 1/3 the way full of PEG oil staring with an empty system?".
Typical answer was ,,"well, closer to 1/4 of the way full with a dry system but that all depends on the line length".
so if you fill the compressor completely and manage how many cc's were put in, empty back out 3/4 of that and you have a good start. With dry lines, it puts you at an oil level closer to 1/4 full. To be honest, no one is going to give more straight of an answer. I am just sharing what i have observed.
Take a look at some big rig engines and eyeball thier compressor, you might see the sight glass im talking about.
once you get the oil in, pulling vac and charge is easy.
getting nothing but air out now (ie- r12 or 134) is normal. If i hit the purge valve and got oil, I would know i just found my problem,, too much oil.
Sounds good - I have a compressor from ackits.com that I believe was new - don't remember seeing a sight glass but it may be there...
you could in theory jumper the presure switch connector to keep the compressor on,, with the right amount of oil, its just going to get purdy hot.
The AC system is just a large loop, evacuating low also takes care of the high or vice versa...
Lemme know if you find a sight glass, I've never seen one on any newer system later than the early '80s...
I would more than likely run jumper wires over to the gauge so I could turn it on and off myself so I can keep adjusting the valve.
None of this is working - what part is bad? I tried a different approach that seems to be getting me into the same trouble. With the car off, I again pulled vacuum on the system, cut it off, connected a canister, purged the air in the fill line, then filled the high pressure side with the canister upside down. As it stopped filling, I closed the valves, purged the fill line again or liquid, then opened the canister and purged air from the fill line and started the car. Before I even had a chance to open up the low pressure line, the compressor cycled a couple times before coming to a screeching halt and not running anymore. Jumping it wouldn't turn the compressor. It is acting like I have liquid in the low pressure side but I've only put refrigerant into the high pressure side so far. Both are reading ~50psi. I had this problem with the compressor earlier filling from only the low pressure side with the canister upright so I figured I'd pull vacuum and try over again.
During this time, filling the high pressure made the low pressure eventually ease up to 45psi by the time the car was started. It dropped to 35psi on the first couple cycles and then stopped altogether.
Does this mean I have a bad orifice tube? Compressor's just shot? It's getting 12v when I manually jump it but the thing is locked up hard and the clutch can't engage. Earlier prior to this attempt, it kept cycling between 25-48psi (on at 48, off at 25) but the high pressure would never build more than 60-70. Manually running the compressor it would run continuously but the low pressure never went below 40psi and the high pressure wasn't going anywhere over 50. I found this extremely odd. The clutch should be fine, it just can't go in after it hits a certain amount of refrigerant in the system.
Quit worrying about high vs low, should always charge from low side, like I said before, the AC system is just a big loop... If it's locking up after charging only a pound or so you likely have a blockage, probably the expansion valve(orifice tube) has crud in it...
BTW what's the air temps??? If it's below 55* or so, evacuation may not boil all the moisture out of the system and the orifice is freezing...
75ºF.
So should I not worry about being able to see refrigerant as long as the can is up right? I've tried to keep the pressure relatively low to help prevent more than gas from escaping the can.
If the compressor's cycling then it should be fine? I'm not sure how the compressor itself separates the high and low pressure sides and if anything can leak by. I guess I should replace the orifice tube which means again replacing the acspoogeulator also.
Edit:
If there is a blockage, shouldn't the high pressure side increase if there's plenty of r134 in the low pressure side? Everything I've read about blockages is causing extremely high pressures when running. I seem to have an equalized system that won't compress a thing.
Uhhhh... Yes if there's a blockage the HS pressure should be extreme... Guess I was getting sleepy when I made that post...
Internally the compressor is similar to a engine, pulls in on the low(intake) and pushes out on high(exhaust)side... Yes there is pressure on both sides, but the high is always trying to equalize the system by flowing to the low... There are valves(probably reeds) internally that block the flow from reversing... Those components can be defective and keep the compressor from pumping at all, but I've never seen one lock because of this...
Possibly it's not locking at all and you have a defective clutch(only partially engaging)??? How does it act with a straight 12V applied??? I had one with a defective pressure switch, that had internal resistance and would only weakly engage the clutch... Worked fine idling, but caused the clutch to slip at higher RPMs(when I drove it), thing like to have drove me crazy...
Just reread your posts and if you aren't building HS pressure, compressor may be defective... Unfortunately the orifice tube can act similar... The orifice is the point where high vs low meet and is basically a metering device... It causes the refrigerant to "dam up" and slowly enter(expand) into the acspoogeulator then enters into the evaporator... This expansion is what provides the cooling(same as cranking open the valve on a can and dumping it into the atmosphere)... If the orifice isn't providing metering, the system pressures will be close to equal(lo vs hi) and due to no expansion of the refrigerant, you'll get no cooling...
When I have low pressure in the entire system, jumping the compressor clutch would spin continuously but the low side pressure was never decreasing (against what was happening with the cycling where it would decrease on the low side and build for a second on the high before cycling off). I'm seeing weird behavior so something's gotta be off but due to the slow nature of the high and low sides equalizing, something's gotta be working also. I'm assuming the compressor is messed up.
So I had a shop look at it and before they even looked at one important fact, they did some diagnosis on the system. After realizing it's running r134, they stopped and told me so. No charge, but they think that there's a blockage, even with the lack of high pressure. Soooo, I guess I'll pull the system apart at the condenserand gas line and check for blockages. I figure if I'm doing this, I may as well replace the condenser.
Has anyone tried installing a larger condenser, namely a 97-98 Cobra one? It appears that besides mounting brackets, it should go right in. Also what company should I trust for this part? It's high pressure so I don't want something that'll rip open.
What's the cylinder near the compressor? Just a ler? Why the foam? The replacement discharge lines don't have it...
I also like the $100 97/98 condenser price on rockauto, not too bad.
Okay, so I put the new condenser in, along with a new acspoogeulator/hose and liquid line. The compressor still gets to a point where it won't turn on anymore. It only hit ~100 psi on the high side, around 30 on the low before it quit spinning when I had the switch jumped. The compressor just comes to a screeching halt at this point and rejumping it makes it only turn on for a split second before halting again. Now it won't even engage. I hope the compressor isn't bad as it has next to no use on it - it's not a cheap autozone replacement either.
Perhaps a weak clutch? One would think it would engage either way as long as the clutch/bearing/coil are fine.
Have you verified that 12V is coming to the clutch? If so, and the clutch isn't engaging, you have a bad clutch or your air gap is too big.
12v yes - the clutch tried to engage but stops pretty quickly and won't turn anymore. I can turn the inner area of the pulley by hand easily. I'm going to just install a replacement and then take this one apart to see what is wrong with it. I've got spare parts of everything else, why not an a/c compressor also?! :hick:
Okay, so I tested some things. Jumping the compressor from the battery works all the time. This draws 3 amps. When jumping the positive from the pressure plug and grounding to the battery, the current draw is only 100mA (13.6v - doesn't drop with the compressor connected or not). WHAT would cause my amperage to be so low?! I tried replacing the 20A fuse thinking perhaps it was old and tired but no go. Must I start testing the wire from the HVAC controls?
I could hack it together with a relay but who knows how long that would last.
Edit:
I didn't do FULL tests earlier. I found in the end that jumping from the pressure switch straight to the clutch coil draws exactly 3A and engages the clutch. I can't seem to pinpoint some wiring diagram for this - does anyone have one? The wire is good from the pressure switch to the wire harness and the wire harness to the compressor (tested with poking a hole in the insulation right outside the harness).
Is one of the relays on the passenger side shock tower the WOT cutoff? This could perhaps be the issue...
problem solved - bad wot relay.
New problem! The system holds 29" of vacuum for hours but whenever I get up to around 170psi dynamic on the high side (tried two different charges with replacing all the orings again between the two), all of a sudden it goes downhill and my gauges start reading lower and lower. I was at 80psi static until I went to add more than 24oz - the third can dropped it to 70psi static and the liquid line gets barely cold and the condenser stays cool. It holds pressure though. High side is up to ~180psi before the pressure switch turns the compressor off. It was cooler at 140psi high when it was at a static pressure of 80psi. What would be causing this?! It makes no sense!
Edit:
This is with an ambient of ~90 degrees
180psi on the high side sounds a bit low... at what low pressure is the compressor cycling? And, is the compressor cycling quickly, or slowly? If I remember correctly, on a 90* day on high fan you should be seeing high-side readings of around 250psi and your cycle switch should cut the compressor right around 32psi low-side.
Shiny Side Up!
Bill
I've currently got it set to cycle off at 22psi. It takes about 30-40 seconds from when it's on for it to turn back off. It comes on at ~50psi low and off at 22. I had a hot condenser at 150psi high but it's cool at 180psi, along with the liquid line being warm. It's like it just stopped cooling completely.
22psi is way too low, the evaporator will freeze up... maybe this is what happened? With 134A you may be able to go as low as 28psi, but anything lower will put your evaporator temps below 32* and cause the formation of ice across it. This will cause the a/c to blow warm air, and may cause the inverse pressures you experienced as the system will no longer be absorbing any heat from the evaporator. No heat means no pressure, and your pressure of 22psi roughly equates to an evaporator temperature of 25*F.
Shiny Side Up!
Bill
Here is a chart I found: http://www.csgnetwork.com/r134apresstempconv.html
Shiny Side Up!
Bill
Interesting - so the information I've found from numerous sources telling me to adjust the screw in the pressure switch to 21-22psi low (from 25 stock for r12) are wrong. Most information on the net is taken from the same original source anyways. To what extent should the r12 parts (with proper desiccant acspoogeulator) work with r134 refrigerant? I think my liquid line's got a standard orifice tube that lets too much refrigerant by, preventing proper 240-250psi high side pressures before it leaks past to the low side.
I will give this a try.
I have worked only on 4 AC systems (2.5 retrofits and 2 "top offs"). I have been learning alot since moving to San Antonio however (its 102*F outside right now.....kill me).
I did find this chart: http://www.hvacmechanic.com/refrigerants/ptcharts.htm
If you look up R12 at 25 psi (yellow), that equates to 26*F. If you follow 26*F over to R134a (light blue) it occurs at about 23 psi. So what seek said, makes sense to me. An equivalent pressure for R12@26*F 25 psi equates to R134a@26*F 23 psi.
I'm not telling you to do it, I can understand why someone would tell you to adjust the switch. If you left it at 25 the coldest R134a would get would be about 29* so you would loose about 3* of cooling capacity.
I assume the system is designed to work with a minimum of some cfms of airflow across it (hence the R12 temperature being lower than 32*c). I wonder what freon temp ice begins to form.
In all the years I was wrenching, I never set an R-12 cycle switch to cycle off below 32* (about 30psi), and I adjusted many of them. If the evaporator surface temps drop below freezing, the water in the air will freeze to the evaporator and clog it.
Shiny Side Up!
Bill
Okay, so when I went out there again to try to finish charging it, the static was at 90psi. I can only fill it to about 29-30/220-225 before it won't build anymore - I blame the orifice (more easily clogged if smaller) and/or the compressor itself (better to replace) for the inability to separate the two sides of the system more. While I DID have some icing of the liquid line before, it just builds moisture slowly now.
So going off of this whole temperature thing, does that mean that this system is now slightly overcharged (maybe ideal)? I should be shooting for 26-28 psi for r134 in order to get near freezing? I haven't seen the actual concept of phase change but I assume the high pressure is built to better cool the liquid (and turn it to liquid period)? Please help me understand if this is correct - now that a big project at work is complete, my mind is much more relaxed and these things now make sense :p
With our engine bays and headers right next to the liquid line, is ~30 degrees/26psi ideal since it is so hot in the area? Without a larger evaporator or more efficient refrigerant, there isn't a whole lot more to gain I would assume - just stick it on max ac and wait. What affects what exactly to improve a/c performance on newer cars? Everything?
Edit:
This was only at ~1k rpm's - I assume the temperature would be lower at higher so perhaps I am in a safe spot. I will mess with it tomorrow at higher rpm's after the system has some time to settle and I can get another static reading. I'm sure this may help the compressor a bit more and let me dial in the pressure switch a little better.
The way it works:
The compressor turns the refrigerant into a High Pressure Gas, as when you compress anything, it becomes hot.
The High Pressure Gas then goes through the Condenser where the High Pressure Gas is cooled to become a High Pressure Liquid.
The High Pressure Liquid is then passed through a metered orifice releasing the pressure. When you release the pressure the High Pressure Liquid expands becoming quite cold, entering the Evaporator as a Low Pressure Liquid.
This Low Pressure Liquid is then passed through the Evaporator where it Absorbs the the heat in the air passed through the atmosphere side of the evaporator causing the refrigerant to become a Low Pressure Gas which then makes its way back to the compressor.
Note that the A/C system Absorbs Heat from inside the car and releases is outside the car.
Shiny Side Up!
Bill
What was the outside temperature? What was your vent temperature with he system set at Low Fan?
On a 90* day, with the system set on Normal, Low Fan, you should see outlet vent temps around 50*. A 40* drop in temperature is quite good. With the system fan set on High and the engine running around 2000 rpms, the outlet temps should stay around the same, but your high side readings will go up a bit as you will be pulling the heat from a greater quantity of air.
Ideally, in an R-134A system, the inlet line to the evaporator will be a couple of degrees cooler than the outlet line, and your High Side readings should fall somewhere around 2.5 times outside air temperatures.
Shiny Side Up!
Bill
Low pressure on the low side = cooler temperatures but what exactly does higher pressures on the high side do? Just allow more heat transfer in the condenser?
High side pressures are, more or less, simply a function of low side heat absorption coupled with how full the system is.
Shiny Side Up!
Bill
Wouldn't more refrigerant with the proper compressor and expansion valve/orifice allow more cooling? I see people talking about r134a pressures of 300+ on the high side and figure it just allows better heat transfer to the condenser.
The import cars I have that use expansion valves tend to have higher high side liquid pressures. I believe this is because the valve dynamically changes the amount of freon being let into the evaporator. The ford system (and gm and most domestics) use the orifice tube which is about as dumb as they get and will always allow the same amount of freon through. For example, the 95 pathfinder cools best with a 300+ high side, my 03 Jetta likes 260-275 with a low side of around 30-35. These results obtained using a thermometer in the vents.
I typically will vent the system till I start to see the temperature rise a little. Then charge in small increments checking the thermometer until it hits the low "flat spot".
If you are really worried about the orifice tube, change it out. I just replaced my liquid line with one from advance for ~$30. I cut it open and it was full of crud (from the last compressor barfing). I would watch the compressor charge up hit 350 and shut down. The low side would drag down to 10 be very slow to recover. I think I am going to replace the condenser as well as it seems to have restriction of some sort.
I also took this opportunity to flush the system with mineral oil.
Yeah, I don't have any obstruction issues and besides the compressor and discharge line, all the rest of the parts are new/cleaned (which aren't old to begin with). My orifice tube is the stock r12 one - it lets more refrigerant past to the evaporator than I can get put into the high side - continuously runs the compressor at around the 30/225 mark.
I have to mess with it some more as my cooling doesn't seem any different at 30/225 than when I was only at 180 on the high side/low charge with the compressor cycling. There was no "sweet spot" in between here either but not I don't have to hear the compressor continuously kick on and off.
Take a deep breath :)
Measure pressures at 1500 rpm
On Max A/C
Doors open or windows down
Are you charging with R134a 12oz cans? If so, put them in a bowl/can of hot water to make charging easier. The temperature increase will increase the pressure in the can and increase the flow rate from the can to the low-side of the system. If you shake the can and you feel any liquid swishing about, you haven't gotten the full 12oz of refrigerant out yet.
***Keep in mind if you get the water too hot, you could blow the can up***
Our systems take ~40oz of R12. R134a conversions generally take ~85% of the R12 capacity. ~34 oz in our case. The PF condeser throws a wrench in the works as it has a different volume than the tube/fin condenser it replaced. I would hazard the PF condenser has less volume, but that is a WAG.
Regarding static pressures. When you have a saturated mixture, the pressure is simply a function of temperature. You have a saturated mixture when there is both liquid/gas present. If you slowly filled the system on a 90 degree day, you'd see the pressure go from -29.xx in Hg to ~105 psi and then level off. It will stay at 105 psi until the system is completely filled with R134a. That is why you can't judge charge by pressure. It could have .5lb or 10 lb and the same pressure would register.
A clogged orifice tube would cause short cycling because it tends to create a vacuum after the orifice.
To charge the system:
Use the hot water method to dump as much refrigerant from two cans while the system is static. Don't worry about the residual refrigerant in the first can as we'll get to that later. (You need two can taps to do it this way)
Crank the car, run at 1500 rpm, max ac, high fan, doors open/windows down
Note hi/low pressure and center vent temperature
Suck the rest of the refrigerant out of the second can using hot water again
Note hi/low pressure and center vent temperature
Add the rest of the first can
Note hi/low pressure and center vent temperature
Start on third can
Note hi/low pressure and center vent temperature
What you'll find is pressure will keep going up and then they'll plateau. This is the point where you now have liquid exiting the evaporator. You can add 4-6 more to get to the correct charge.
If you don't want to pay attention to evaporator inlet/exit temperatures, just keep adding until you see the vent temps start to rise and then remove 2-4 ounces. Keep an eye on the pressure the whole time to make sure the high side isn't running away.
In general, the high sides will run 2.2-2.9 times the ambient temperature. So the high side will be ~200-260 psi on a 90 degree day.
What fan speed and what rpm?
What is the center vent temperature?
HVAC on max a/c/"high" speed (position 4 only gives me position 3 now - I need to put rotary controls in. I used to be able to push the switch sideways to make high come on), mechanical fan with new standard output thermal clutch NOT at 1500 rpm's (haven't gotten around to rechecking with higher rpm's quite yet), vent temperature is only ~25 degrees cooler than ambient with the two passenger side vents closed - there's some wire in the way of their doors right now so they can't be opened). I have only tested this so far with 90+ degree ambient. The condenser doesn't get warm/hot enough to be uncomfortable to place my hand on the front. Liquid line and acspoogeulator tubes coming out have light moisture buildup after ~10 minutes. Return line is cool at the compressor - discharge is scalding.
I do not get better cooling going down the road than idle.
I'm guessing you're undercharged.
As ProTouring said, you want the evaporator outlet/inlet to be close to the same temperature. If the outlet is noticably warmer, then you don't have enough refrigerant in the sytem. The refrigerant is boiling off before it comes out of the evaporator. Ideally the evaporator is 'flooded' and liquid exits into the acspoogeulator.
A system with an expansion valve will have have an outlet ~6-12 degrees warmer than the inlet. The valve senses the temperature difference between the inlet/outet and changes the orifice size to achieve the desired superheat*. If the superheat is too low (outlet 2 degrees warmer than inlet), the orifice will get smaller. If the superheat is too high (outlet 20 degrees warmer than inlet), the orifice will get bigger.
*Superheat is how much hotter the vapor is over it's saturated state. If you have a pot of water at 212 degrees at sea level. It would be a saturated liquid. If you boil the water, it is a saturated vapor. If you raise the vapor to 222 degrees, you have a superheat of 10 degrees.
Okay, so perhaps I am understanding this a little better. I went to mess with the a/c and found that at "1400" (stock gauge - probably closer to 1300 if I datalog), if I wait for the lines coming out of the evaporator to just begin to freeze before cycling the compressor off (23psi on the gauges), I get the coolest temperatures. I am not sure if this is fine or if I should raise it 1psi on the low side (lines don't even get close to freezing) but I figure the frozen fins should quickly thaw when it cycles off, a bit slower than the lines in the engine bay with all the heat.
At idle, the system can barely get below 30psi on the low side before the compressor can't keep up any longer. Of course, temperatures are much warmer but both idle never cycles off and 1400 rpm's cycles at about 10 minute intervals. Should I charge it just a tad more to always prevent freezing of the return line? It freezes at the compressor at about 24psi and on the acspoogeulator side at around 23psi. I assume that as long as there is basically no moisture in the system ("20 micron" pump) and the evaporator isn't clogging up, shouldn't the system be fine with the above numbers?
I wouldn't add refrigerant at this point because your icing at 1400 rpms is a function of your cycle switch.
On a hot day, it is likely the compressor will not cycle at idle, so as long as your high side readings aren't out of sight, I think you're OK.
Drive it and see what happens. If on a highway cruise you loose a/c due to the evaporator icing over, then I would bum your cycle switch up one psi/*, otherwise, you are probably in good shape.
Shiny Side Up!
Bill
Guys, another summer is here and I'm finding weird issues with the system. At idle, I'm seeing 40psi low, 250psi high and at 2000 rpm's I get 30psi low, 325psi high. I adjusted the switch a half turn as it was turning off whenever it saw anything lower than 30psi. Why does it take 2-3 minutes before the compressor kicks on again when this would happen? Also, why after 15 minutes or so of driving (it can be stop and go or it can be highway), the compressor continues to run and gets near freezing while the cabin temperatures are still about 70?
I get the following center-vent temperatures on a 90 degree day:
Turn on AC and within 1 minute I'm down to 65 degrees
Two minutes and I'm at 55 degrees
Compressor cycles on and off two to three times for the first 15 minutes.
Half the time the AC stays around 52 degrees vent for the rest of my drive
Half the time the AC drops to a vent temperature of 38 degrees for the rest of the drive...this happened today and I kept it going - when I got to my destination, my hand was still cold about 5 minutes later.
Why are my pressures so high now compared to last year when the system has not been touched and the temperatures are the same? 325psi high should be closer to 250, correct? Any lower pressure and my low pressure switch will begin to cycle unless I drop it down to cycle much lower...
I use a Fluke 561 for my temperature readings with the contact probe intertwined with the vent.
Now my low pressure switch is turning off at 45psi and screwing the adjuster either way apparently does nothing and I cannot hit a stop in either direction (should I?). It doesn't explain my earlier issue but this switch is bad, right? If I'm replacing it, I figure I may as well replace the orifice tube with a variable one? Is there one you guys would recommend or just pick up any ole' VOV from the parts store?
Messed with it a bit more and it seems that once the cutout fires, a second later it tries to turn back on for a second before shutting off, and another second later it flicks on and then back off permanently. Messing with the screw, all the way turned in and back out, it'll work again but not if I hit around the cutout area again. At 70 degrees, it is dropping down to 28psi low/150psi high at idle, 19psi low/195psi high at 1500, and 17psi low/210psi high at 2000.
I got down to 39 degree vent temperatures in the driveway with the doors closed for a couple minutes, 45 or so with the windows down. I'm sure it'd ice over terribly (and perhaps not oil well?) if I don't replace the low pressure switch.
So yeah - appears bad low pressure switch to me. Should I try getting a Motorcraft piece from Ford or just grab one from the auto parts store? Still, what about the variable orifice tube? Is there a Motorcraft part number or just grab a parts store unit?
You won't need to open the system to replace the switch, so I wouldn't mess with the orifice tube.
As for the pressure switch, and decent aftermarket one should be fine. Just make sure it is an adjustable unit.
Shiny Side Up!
Bill
Wait - I thought it was o-ringed and touched refrigerant directly? I know I'm still using an original unit from likely when the car was new so it's time but I don't want to pull it out and have the system purge all over my fingers...
Autozone's (Chilton?) repair guides also say to evacuate the system?
The cycle switch screws onto a schrader valve , you should not lose any measurable amount of refrigerant :D
I just replaced the one in my fathers old F150 about a month ago
Correct... it crews onto what is basically a charging port and should have a schrader valve.
Shiny Side Up!
Bill
Thanks guys - that will do. So do my pressures from my previous post sound about right for a charged system? I know the less refrigerant there is, the better it will cool on hot days but it also means more cycling in the cooler months and with the defroster in the winter.
I'm still not sure why I'm getting over 300psi on the high side on a slightly warmer day though. The condenser was only slightly warm (large 1997 Cobra unit) and the engine fan is new.
Edit: In the driveway after a commute, my radiator was ambient temperature within a few minutes. Fan works very well, alongside the 3 core aluminum radiator.
Replaced and the system works great now. Old oring ripped but I've got dozens of AC ones around. So after all this time, the title of this thread is finally coming to a close :p
Good news , congrats ;)