heater fan lost power.

Topic: heater fan lost power. (Read 7435 times) previous topic - next topic

heater fan lost power.

Reply #30 – February 07, 2014, 07:25:58 AM

What do you think of my position that the blower is responsible for the open thermal limiter, now? I also told him to look at the blower switch for signs of melting.
My entire thought chain:
Bad blower -> high current -> more heat in circuit -> open thermal limiter -> only functions on high -> draws most possible current -> overheated blower switch -> 1. possible blower switch failure, 2. possible blower motor dead

heater fan lost power.

Reply #31 – February 07, 2014, 08:29:35 AM

Foe if by now you actually think you are going to get some common sense from the original poster you are NUTS. But here goes on your theory which i believe is correct by the way. . Those Thermal limiters showed up @ or around the vintage years we are dealing with. Now many companies use them and some were marginal at best. So i have replaced many over the years that did not require a motor change out. As the matter of fact MICE NESTS plague us up north. I have removed many a MOUSE from a blower motor!!! Many did require a change out. As debree and bearing drag increase current rises and loads down the circuits more. Naturally over time it loads down the connectors switches and thermal protectors. This is still going on today!!! I keep several connector UP DATE kits in the shop for GM FORD AND CHRYSLER. Yes what you posted is correct and factual as far as his issue is concerned. But getting that in to his head is another lost cause, Thanks

FOE i need to ask you a question on a cranking issue on a 4.0 Explorer if i may. I might have to move this to Genrtal but here goes. I have a customer with a 1999 4.0 explorer that sometimes when cranking it seems like the timong advances and the engine lugs before firing. Another words it cranks fine to the point of the second it ants to stare if seems like the timimg is advanced 30* and it slows down. It always starts but it is do dam intermittent i can not put my finger on it. It almost sounds likie a cross fire before starting but the dam thing runs and drives perfectly. Any ideas?? Thanks

heater fan lost power.

Reply #32 – February 07, 2014, 08:43:50 AM

That's a SOHC 4.0L?

Maybe we do this via PM.

heater fan lost power.

Reply #33 – February 07, 2014, 12:40:49 PM

Sohc is correct

heater fan lost power.

Reply #34 – February 07, 2014, 12:46:41 PM

Chain noise on cold start?

heater fan lost power.

Reply #35 – February 07, 2014, 02:05:12 PM

Not really it had the recall dun by the dealer

heater fan lost power.

Reply #36 – February 07, 2014, 02:20:53 PM

Foe, not trying to step on your dick here, but I'm looking at a current draw chart in the 84 shop manual.
Tell me what you think.
The motor current draw Hi= 7.0 amps Med= 3.5 amps Lo= 2.0 amps.
The Med resistor cuts the current draw to half the Hi current.
Lets say for discussion purposes the motor with a locked armature drops to zero resistance.
The current draw on Med would go to 7.0 amps.

I don't have one of these resistor assemblies to look at, but in places I have looked that sell thermal limiters they typically have a current rating of 15 amps.

If the motor is struggling to run on Hi it could stall on the lower speed settings.
The resistor now has twice the normal current and no cooling air flow.
The source of the heat to melt the "wax" to allow the spring loaded contacts in the limiter to pop open is the resistor overheating.

heater fan lost power.

Reply #37 – February 07, 2014, 03:05:29 PM

According to the 1986 spefications book, current draw on high SHOULD be 11-13 amps, and I pulled the resistor from my old heater box (because I almost never throw things out) and the thermal limiter is labeled 15A. We should consider that if you placed an ammeter across the blower circuit from the fuse to the ground, current would register nearly the same whichever speed you are set at, the resistor limits the current through the blower by consuming current itself (this is why we have to cool the resistor). We can assume then that under the best of conditions we're within 2 to 3 amps of the thermal limiter's capacity at any time when the blower is being operated. Is it really that hard to imagine a 28 year old blower drawing 2 to 5 more amps? And remember that with voltages fairly constant, the draw for each resistor stage is static, so the resistor can never draw more current that it was designed to, but the blower can. The blower can draw as much current as is available to it if it needs it to spin (assuming, of course, that it CAN spin). And a thermal fuse as used in a blower resistor is not a wax type thermal fuse. It's more like two electrical terminals connected by a length of solder (although it isn't solder). This is different from an old AC clutch thermal limiter or one like you would find in a dryer.

heater fan lost power.

Reply #38 – February 07, 2014, 04:07:46 PM

Quote from: TheFoeYouKnow;428587

. We should consider that if you placed an ammeter across the blower circuit from the fuse to the ground, current would register nearly the same whichever speed you are set at,

I am guessing you mean volt meter. If you hook up your ammeter like that, you will blow the fuse in the meter. The current through the fuse and everything else in the circuit will be the same as the current through the motor.

Quote

the resistor limits the current through the blower by consuming current itself (this is why we have to cool the resistor).

It reduces the amount of current flowing in the entire circuit from the fuse to ground.

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We can assume then that under the best of conditions we're within 2 to 3 amps of the thermal limiter's capacity at any time when the blower is being operated.

When in Hi, no current is flowing through the thermal limiter. Using the ratio I posted, at Medium speed you will have half the 11-13 amps flowing through the thermal limiter. At Lo speed you will have even less.

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And remember with voltages fairly constant, the draw for each resistor stage is static, so the resistor can never draw more current that it was designed to, but the blower can.

The resistor is in series with the motor. In Med or Lo all the motor current has to come through the resistor. The resistance of the circuit is the resistance of the motor added to the resistance of the resistor.

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The blower can draw as much current as is available to it if it needs it to spin (assuming, of course, that it CAN spin).

In Med or Lo the current draw is limited by the resistor in series with the motor.

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And a thermal fuse as used in a blower resistor is not a wax type thermal fuse. It's more like two electrical terminals connected by a length of solder (although it isn't solder).

How is this any different than a fuse?
With the speed switch in Medium, if you shorted out the motor the current draw through the thermal limiter would be 11-13 amps limited by the resistor.
To sum up, you are never going to draw more than 11-13 amps through the thermal limiter, no matter what the motor does.

heater fan lost power.

Reply #39 – February 07, 2014, 05:50:29 PM

You're nit-picking me to death here and completely missing the point. And the point is that Stacks' blower is junk. The resistor is open, because the blower is junk, and if the blower turns out to not be completely dead, his blower switch will probably be melted down. In all scenarios, he needs a blower and a resistor, possibly a switch, and no matter what, he's got to pull the dash to change the blower. You can argue semantics and fine details with me until rapture, but none of it changes these facts.

heater fan lost power.

Reply #40 – February 07, 2014, 07:09:56 PM

Quote from: TheFoeYouKnow;428595

You're nit-picking me to death here and completely missing the point. And the point is that Stacks' blower is junk. The resistor is open, because the blower is junk, and if the blower turns out to not be completely dead, his blower switch will probably be melted down. In all scenarios, he needs a blower and a resistor, possibly a switch, and no matter what, he's got to pull the dash to change the blower. You can argue semantics and fine details with me until rapture, but none of it changes these facts.

You are absolutely right about what it will take to fix the problem.
I just thought you were a details guy who would appreciate knowing how and why the limiter works.

heater fan lost power.

Reply #41 – February 07, 2014, 07:42:57 PM

fast backwards a little bit.

post 1 clearly stated he "use" to have high only but now nothing.

so Major tom,, there is no relay in this OEM circuit
Can you please ignore the fact that people ask the same questions over and over again,, just enjoy answering because its why this board is here.

Foe,, your agreeing with us on everything except how you call things or what they are named,, either way something broke shiznit from the the source on down stream.
the whole circuit is kaput.
so,,, till haystack comes back and tells us what does work,, its all speculation.

heater fan lost power.

Reply #42 – February 08, 2014, 07:22:26 AM

JAY 40 posts on a blower circuit that is the bottom line of simplicity is MIND BOGGLING. But it did do one thing!!! At least it shows Stacks that when a motor slows down it draws less current. As far as the limiter goes years back they did not even EXIST!!!! Just speed resistors. Most high speed fan circuits are 30-40 A and the lower speed are normally 20-30A. JAY I NEVER SAID A RELAY WAS IN THE CIRCUIT. Clearly the print does not show it. I can read prints very well JAY. But this circuit is a ground variable setup instead of a battery one. Not that it makes a difference it does not. The motor sees less voltage and current to slow it down either way.

heater fan lost power.

Reply #43 – February 08, 2014, 07:30:55 AM

Just for the record here the thermal limiter in this circuit has nothing to do with MOTOR SPEED. It is exactly what it is called a ONE TIME FUSE OR THERMAL LIMITER. It has a fancy name but it is basically a ONE TIME FUSE GUYS NOTHING MORE!!!!!

heater fan lost power.

Reply #44 – February 08, 2014, 07:35:43 AM

To sum up, you are never going to draw more than 11-13 amps through the thermal limiter, no matter what the motor does.

WRONG!!!!

If in fact the motor armature or cage is locked the current would go through the moon on either LOW or Medium setting and until it reached the capacity of the 30 amp fuse or the capacity of the limiter whatever that is. and at that time the 30A fuse or the limiter will blow rather nicely. Personally i do not know which one will POP FIRST as i do not know the current capacity of the limiter. Naturally on high the 30A fuse will be the natural choice of sacrifice!! If memory serves me those thermal limiters are there to keep the resistors from overheating and nothing else That is why they are called thermal limiters.