A/C system

Topic: A/C system (Read 10914 times) previous topic - next topic

Reply #45 – July 13, 2013, 09:03:45 AM

Quote from: Seek;418528

Our low pressure cutout switches also are adjustable. ?

say what????????????????????

A/C system

Reply #46 – July 13, 2013, 02:08:57 PM

Quote from: jcassity;418539

say what????????????????????

There is a set screw on the low pressure switch. While not really needed for adequate cooling, the cutout can be adjusted quite a bit to change when it engages. To cutout at the same temperature as the stock R12, R134 would need to have the cutout switch 3psi lower. This is only a 3 degree difference though, and it won't do a thing if the pressure isn't getting low enough in the first place (inadequate condenser performance).

A/C system

Reply #47 – July 13, 2013, 03:01:13 PM

I'm confused. I guess I'm not the only one running lower low-side pressures. I found this thread: http://www.stangnet.com/mustang-forums/threads/fox-r-12-pressure-switch-or-r134a-low-pressure-switch.869321/

I believe the stock system is set to cutout around 30-32psi though, not 25? From what I see, many cars seem to cutout around 25psi, so that is a bit different than I remember. I could be remembering temperature instead of pressure though.

Also, if I remember correctly, the compressor may start to have problems if running <15psi low side.

I should test the A/C in the car again to see what it's actually at. I'm pretty sure my high side pressures were higher than expected also, although I think I have a stock orifice tube. By higher, I mean 220psi on a cooler day and closer to 300psi on a 100F day. This with a 20-22psi low pressure would mean that the compressor is pumping too effectively for the side of the orifice tube. I believe these numbers were at speed (3x idle rpms), and not at idle. This was also sitting in the driveway though, with next to no airflow. I think I had a mechanical fan at that time, with a bad clutch. The pressure would be quite a bit lower driving down the road, or with my electric fan.

A/C system

Reply #48 – July 16, 2013, 10:10:30 PM

Quote from: Seek;418528

Does it cool well if you're on the highway?

If so, installing an electric fan to run with the A/C on will help your cooling, as would a larger condenser.
If not, I'd look at there being a problem in the system. Too much refrigerant, or not enough will affect the low side pressures, which are what flow through the evaporator.

Our low pressure cutout switches also are adjustable. r134 will cutout at a temperature 3 degrees higher than r12. If you adjusted the cutoff to be 3psi lower, the cutout would be at the same refrigerant temperature. I'd guess your problem isn't the system being 3 degrees different though - something wasn't installed right. For the best cooling, run a refrigerant level that stays just above the cutout switch pressure level on the hot days. I'd say shoot for 40psi low side at 1500rpms on a 100F day for a good dummy-proof system (45F evaporator temperature). Most cars today limit the cooling potential to around 60F anyway, so it would be nothing different than what people are used to.

Did you just have refrigerant added by a certain weight, or were gauges used to get the proper charge amount?

It cools ok to well on the highway. I do have an electric fan, pretty big one too. Not sure of the cfm rating but it flows. Problem is most if not all of my driving is city bumper to bumper. At first I put in the 1.33 kgs it said for R12, but obviously that was way too much. I did some reading about what some people have done and they put in about 80% of the R12 charge, so I put in 1 kg. Still too much I think. My high side pressures are 315 psi and low side 60 psi. Tomorrow if I get the time I'm going to pull a long 30-45 min vacuum and put a little less in. I usually shoot for low side in the 30s. Most of the customers cars I deal with I still get pressures around 175 high side and 30 low side with vent discharge temps in the low 50s-high 40s. Although that's on newer cars.

I work at a dealer so I have all the equipment and it's easy. I was just curious if anyone had gone backwards. I will someday try the cobra condenser and flush the system out real good again, but that's when I get a good teardown and rebuild on the car. Can't afford that right now, haha.

A/C system

Reply #49 – July 17, 2013, 06:23:39 AM

Your low side is to HIGH and the high side as well. with a CCOT this points to a bad compressor . Without seeing the car that would be my guess. Having a high side of 300+ cant be good.

A/C system

Reply #50 – July 17, 2013, 07:06:11 AM

Have you got enough air across the condenser? Obstructions, blockages, crud between the condenser and radiator? What RPM are you testing at? Charge weight in ounces? Most importantly: Environmental conditions (temp, humidity)? Right now at my shop we're in the upper 90's with matching humidity, I did an evac and charge on a Taurus yesterday and even with the fan running, and the blower on low, my low side only pulled down around 55 psi and my high side was hanging around 300. I sprayed some water on the condenser and high side dropped immediately to around 190 and low side responded by dropping to 30. Mid July weather is a bitch, and you can't explain the concept of a "design day" to a customer because they won't get it in a million years.

A/C system

Reply #51 – July 17, 2013, 12:59:25 PM

Yeah, the cooling of the condenser will have a huge impact on pressures. The cooler the A/C system is, the lower the pressures will be. Highway speeds have a lot more airflow over the condenser, so the pressures drop, and the A/C efficiency improves.

Charging by weight/volume of refrigerant is fine for estimates, but only the gauges will tell the truth. You can also only really ever shoot for ideal cooling in one specific condition. If you want cooler stop and go driving, you need to have good airflow over the condenser and refrigerant levels/low-side pressures down low. This will cause low refrigerant levels at highway speeds, and the compressor to cycle, making highway speeds not cool as well. In cooler ambient temperatures, the pressures will also be lower, causing compressor cycling. While you may not use A/C at lower temperatures, preventing compressor clutch wear from the cycling, note that the defrost also runs the A/C to help dry out the interior. You will get excessive cycling in the winter when using lower refrigerant levels.

They make "variable" orifice tubes that supposedly help low speed cooling, but I believe they are generally not recommended and may introduce problems.

The joys of compromise.

A/C system

Reply #52 – July 17, 2013, 01:04:38 PM

Quote from: TOM Renzo;418786

Having a high side of 300+ cant be good.

With NO airflow/fan in a driveway, I've seen 400+. Not good I agree. Airflow can cut that number in half and make what appears to be "high refrigerant levels" become normal.

Otherwise, with both pressures being higher than normal, the system is over-charged. If the low side is very low and the high side is very high, the orifice tube may be clogged from contamination. Most common culprit here is insufficient vacuum, so ice chunks cause a blockage.

A/C system

Reply #53 – July 17, 2013, 08:44:28 PM

I just finished converting an H valve system to orifice tube on a chevy. Low side @38 lbs High side @ 210 lbs and center vent air 39*@ IDLE. If you pour cold water on a condenser it will always bring down the numbers. Modern air conditioners normally use evaporator water to spray on the condenser. They make a well for the water to collect in and the condenser FAN picks it up and sprays it on the condenser. Naturally cars do not do this. But the engineers know that reducing condenser heat is the KEY for efficient operation. If a system approached 280LBS on the high side something is wrong. Not set in stone but in all the years i have been doing AC that is high. Normally the high side should be 100-120 LBS above ambient or 2,2 -2.5 higher than ambient if the system is correctly designed and working properly. And the low side should be 32-40LBS. This depends on ambient.

NOTE Most automotive systems have a large capacity drier to prevent icing of the orifice tube orifice. A failing compressor is 99% of the time the cause of orifice tube blockage. Just me

If the high side numbers approach 280-300+ the belt and drive pulleys will be overloaded. And if you fast start a shut down engine with those readings the compressor will lock and the belt will do a bounce and squeal. Read my post on the jeep FIX. And @ those numbers the system wont work correctly.

Bottom line here is you need tuns of air drawn across the condenser and fan or fans working continuously when the car is running with the AC running. If not the condensor will run hot and the system will never work properly.

An automotive AC system blowing 55* air is NG and a problem exists at ambient 90*

A/C system

Reply #54 – July 18, 2013, 12:31:58 AM

Dead on.

I think he needs to check airflow first, then refrigerant levels second. Phase change systems are pretty simple.

A/C system

Reply #55 – July 19, 2013, 11:09:42 AM

Ok guys. Not butting heads but, I have worked in a dealer for 8 years. Yes I checked airflow. I have no obstructions in front of the condensor. I looked up the fan, its a Flex-a-lite electric kit that is rated for 3300 cfm, which I think is far more than the factory mechanical fan would do. The ambient temps here have been around 100* every day with humidity anywhere from 30%-100% on average. The charge I put in as far as ounces (I use Kgs because out machine only reads pounds or Kg, not ounces) 35oz, the sticker says it requires 47oz. I had the same feeling about the compressor as well, but seeing as I'm using 134 in a 12 system, I'm not completely sure how it would react. I checked it on a cooler morning about 80* with a big swamp cooler fan in front of the car and it was able to pull down to about 62* discharge temp with low side at 42psi and high side at 230 psi.

Most likely if anything I need a bigger condensor and possibly the compressor, but I just don't want to put too much money into it right now since I plan on doing a big teardown on the car in the next year once I save up some more. I also heard about those Sanden compressors but doesn't sound like many people, here at least, like them all as much. May just stick to factory there. Really I was just curious if anyone had tried going back and forth. I do appreciate all the tips and tricks though.

A/C system

Reply #56 – July 19, 2013, 12:56:21 PM

The compressor is responsible for generating your high side pressures and they are where I'd expect them on a 100F day with adequate condenser cooling (along with the low side being correct). The pressures would drop on a cooler day. I'm sure you know that electric fan will only put out max air at full power, likely requiring a higher voltage to do so, and are running it so. Note that the CFM rating is for open air, and it doesn't mean a thing if you have restrictions before or after the fan (it could drop to <500cfm easily). Shrouds help here a ton, if your fan doesn't have much depth. The factory shroud works pretty well at efficiently moving the air through the entire radiator surface when using the mechanical fan. I would check things in the following order:

1) Is the fan getting air from the radiator, or from the condenser also? Is there a shroud/seal between the condenser and radiator to help it pull air through the condenser? If not, the air that gets pulled through the radiator will be from the area of least resistance. The stock condenser does NOT flow air well, so the air around it will be sucked in instead of from the condenser fins. Good shrouding should help drastically, while using the same, or less, airflow.
2) How hot is the condenser getting? I've never measured mine, but it gets too hot to touch. 120-160F would be a range to look for, the lowend being 200psi and the highend being 300psi. First degree burns can start around 110F and up, if that gives you any value to correlate to. I don't know how hot the outside of the stock condenser would get though. My Mustang condenser gets very hot along the outside of the frame.
3) Try less refrigerant.
4) The compressor could be failing, allowing high pressures back into the low pressure line. What oil are you using in the system since the conversion?

I don't think the orifice tube can break in a way where it allows MORE flow, so that should be fine. If the above are fine, the r134 should work fine. Even the r12 would work better with the above checked or fixed. I would worry that if you converted back to r12, you might find it also performing poorly, but probably a bit cooler in stop and go driving.

A/C system

Reply #57 – July 19, 2013, 01:19:45 PM

If anything, I might add just a bit MORE refrigerant. I'm running 38oz in mine, and even in this heat it's been working great. Having said that, I set up a Fusion fan to run as a 2 speed fan with the low speed being for AC, combine that with my original R-12 condenser and at a stop performance suffers a bit. If anybody knows of a condenser that's more efficient and fits our cars, I might just throw one in.

If you want to know if you're dealing with environmental stress, get a hose and wet the condenser down while the system is running and you have your gauges on it. If high side drops and then low side follows, I'd say you've got a hot condenser problem, which considering the environmental variables involved, you may not be able to do anything about.

A/C system

Reply #58 – July 19, 2013, 05:59:19 PM

Quote from: TheFoeYouKnow;418896

If anything, I might add just a bit MORE refrigerant. I'm running 38oz in mine, and even in this heat it's been working great. Having said that, I set up a Fusion fan to run as a 2 speed fan with the low speed being for AC, combine that with my original R-12 condenser and at a stop performance suffers a bit. If anybody knows of a condenser that's more efficient and fits our cars, I might just throw one in.

More refrigerant will just increase the system pressures. At idle you have two things working against you. The airflow is lower than when moving, so the condenser isn't cooled as well. The compressor is spinning at lower speeds, so it doesn't compress as much of the refrigerant from the low side. Your lower side pressures will be higher and your higher side pressures will be lower. The orifice tube is a fixed restriction, so idle performance will always be lower than at cruise. Thermal expansion valves can change dynamically to make low and high speed temperatures more consistent by allowing it to restrict more at idle when the compressor can't keep up with the loop.

SN95 Mustang condensers are almost a direct bolt in. The line fittings are right where they need to be. I think I just used some metal stock to hold it in place against the radiator support. I'm sure I took pictures way back when, but who knows where they are today.

A/C system

Reply #59 – July 19, 2013, 08:29:44 PM

Plain and simple lets cut through the BS. If your discharge temps are 62* that system is not working correctly. Weather a dealer tech or a weekend worrior that system is not working properly or has an issue. Exact pressure readings and vent temps can be posted. I would like to see what they are doing. Once again 134A is more efficient than 12 and that is a fact. That is why you always charge 10% LOW when converting. Here is a tip if i MAY. Normally an orifice tube should be .065-.070 thousands of an inch. This will support either 134A or R12 nicely. More freon does not mean a colder running system if it is charged correctly. I converted an H valve system to orifice tube. It is 101* today and at idle the unit blows 38-40* Blowing 60* air is not going to cut it . Also is the blend door working correctly. And if possible cut the coolant flow through the heater core and see if that helps. NOTE some engines need full flow through the core so check that out before trying this!!

Conclusion as i see it. Your pressure numbers are close. Normally a low side at 34LBS and a high side at 200 is ball park. So it is time for you to break down the system and check the valve . Or better yet replace it. This is the only way to find out what is going on. One other question is the low side condensing on the hose?? Is it cold to the touch and dripping water including the vent for the evaporator. If it is not condensing the system is in need of repair . just something else to check. Good luck!!