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Compressor quits when hot?

toolman on Thu September 03, 2009 10:03 PM User is offline

Year: 1992
Make: Mazda
Model: Miata
Engine Size: 1.6
Refrigerant Type: R12
Ambient Temp: 85
Pressure Low: 45
Pressure High: 175
Country of Origin: United States

First post and hoping for help! The a/c works well at first and the vent temp is 40 deg. F. But if you drive in stop and go traffic on a hot day the compressor clutch will stop working. If you can get moving without all the stops the compressor will start working again. The cooling system is working well so I don't think that is causing the problem. I know the compressor has a thermoswitch but I'm not sure if that could cause the problem. This is the Phoenix AZ area so it gets extremely hot, like 115! Any help would be greatly appreciated.

GM Tech on Thu September 03, 2009 10:31 PM User is offline

If you are sure the clutch is NOT engaged.....and the cooling fans are working... then.....

Next time you think it should be on- bump front of clutch with blunt object- see if clutch engages- higher mileage vehicles- tend to wear the air gap too wide- and the magnetic pull can't pull the clutch in when coil is hot across that wide air gap-- measure your air gap-- it needs to be at .020" to be good-- yours is probably .050+"

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Cussboy on Thu September 03, 2009 11:11 PM User is offline

Last summer I noticed similar on my '88 Mazda (b2200); since there was clearance I was ready to swap out the AC clutch with an old one I had. But when I went to pull the AC clutch from the truck, engaging the clutch (engine off) and pressing on the belt, I noticed the AC clutch bolt was a little loose !!! So I tightened it, fine ever since, proabably best AC since I've owned it. So also make sure that's tight.

And I'm in Phoenix, so just when has it been "85*F ambient"?????

toolman on Fri September 04, 2009 8:39 AM User is offline

I put gages on it at 5:00AM! That was the only way this time of year to do it at 85F. As you know!
I will check air gap and tightness. Thank you for the responses.

toolman on Sun September 06, 2009 11:57 PM User is offline

I checked the bolt and it is very tight. I also checked the air gap and I could not get a feeler strip bigger than 0.016" to go?
Any other suggestions?

TRB on Mon September 07, 2009 12:50 AM User is offlineView users profile

Might check your pressures when the clutch is not working. As stated be sure you fans are working correctly when the clutch has disengaged! Are you sure the proper amount of refrigerant is in the system?


When considering your next auto A/C purchase, please consider the site that supports you:

toolman on Mon September 07, 2009 2:58 PM User is offline

The low pressure goes up and the high pressure goes down as soon as the compressor stops. When the low side gets close to 50 psi the compressor clutch engages. As far as what happens when the compressor quits when it gets hot I don't know. That has happened when we are out driving and I don't have the gauges on the car?

TRB on Mon September 07, 2009 4:55 PM User is offlineView users profile

In my opinion you must have a set of gauges on a vehicle while the problem occurs. There is just no way to guess that it could be this or that based on the pressure goes up and goes down.


When considering your next auto A/C purchase, please consider the site that supports you:

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