I did a complete A/C service back in February which included replacing just about everything except for the evaporator. Yes, I did the complete flush, vacuum, etc. process then recharging with appropriate oil and 30oz 134A. The system seemed to be working great until recently. It would seem that the compressor stops running at times even though the climate control is set for manual A/C at maximum cooling...this when the outside temperature is 98 degrees.

To be specific, the problem is random. The A/C might work great for 45 minutes then all of a sudden while driving down the road the air gets warm. I've pulled over and opened the hood to verify the compressor is not running even though the climate controller should be forcing it to run. When the A/C isn't working it is common for it to not work for 20 or 30 minutes and turning the climate controller completely off then trying again sometime later the A/C seems to work again. Sometimes, you might just park the vehicle and next time you start up the vehicle and try the A/C works again (maybe an hour or two later).

I thought that perhaps the system was leaking again and perhaps the refrigerant pressure was sitting at the hairy edge of having just enough R134A in it causing the low pressure switch to switch off the compressor. The only way to tell was to hook up the manifold gauge set and check. Below you can see the results which show there's plenty of R134A but then again these readings are coming off the system when the A/C system happens to be working.

I'm beginning to think that the climate controller is starting to go out but honestly I haven't a clue as to what other contributing factors would shut the compressor down when it shouldn't under the scenario I've given above.

Has anyone experienced this problems?...What's the solution?...How do you go about diagnosing the problem?

 

Anyone have any suggestions on where to start? Thanks!

 

You have the automatic temperature control. Your symptoms could be a bad "in car temperature sensor." I don't know if this system uses the temperature sensors in the ducts to monitor HVAC performance. I don't see those parts in the catalog for a 1998 with automatic temperature control.

I'm not sure what year you have, and I haven't dealt with the automatic temperature controls on these trucks. On other GM vehicles, a really good scan tool (meaning a Tech-II from the $tealership, or a very high end tool with software for HVAC and Body modules) can read the codes and current temperature sensor data from the HVAC controller or BCM (depending on the model) and check for malfunctions. If the inside air temperature sensor (usually it's above the driver's door, and it looks like a small vent or a small speaker grill with several small holes) says it's "cold" inside, the system turns off the compressor.

For the 1998-2002 Blazers, it looks like that cabin air sensor is made of pure unobtainum. It's no longer available in the parts catalog, and I can't find any aftermarket cross reference that is still in stock at any of my normal parts sources.

 

One more thing. When it mysteriously stops, switch the controls to full cold and defrost. If it blows cold and the compressor comes on with the controls on Defrost but not on the "Auto" A/C setting, the problem is in the temperature sensors and controls. If it blows hot when set on "Defrost" with the temperature set on cold, then the problem is in the refrigerant system. The compressor always runs (to the extent that it can) when the controls are in the defrost position.

 

Thank you for the reply and suggestions. It's a 1998 Chevy Blazer with 4.3L V-6.

 

After doing some reading I'm thinking the problem could be the pressure cycling switch located on the accumulator/dryer. Could it be the cycling switch is near the end of its life? I reused the old pressure cycling switch when I changed out the old accumulator/dryer.

Would my symptoms point to the pressure cycling switch as the culprit?

 

It could be that switch. If your defroster blows hot when you're seeing the failure, that points more to the two refrigerant switches. There's the one you mentioned, and one more on the compressor, on the suction side of the compressor.

If the defroster blows cold when the AC blows hot, it's probably not the refrigerant switches, because those would make the defroster hot, too. That points more to the "automatic" controls and the inside air temperature sensor, and/or any in-duct temp sensors yours might have.

 

I replace the pressure cycling switch on the accumulator/dryer. This did not fix my problem. I should note that that high pressure switch on the back of the compressor is new as I bought a new one when I installed the new compressor.

With regard to switching on the window defroster when the air blows warm in an attempt to force the compressor on I note that the window defroster air blowing out was was not cold. I did not have an opportunity to look at the compressor when I turned the winder defroster on but assume it was not turning based on having warm air blowing out of the window defroster vent.

Any other suggestions? As I pointed out the manifold gauges show the R134A charge is optimal as I installed 30oz per the manual.

One other thing I should note although it doesn't seem like it would be related to the lack of cold air on occasion but I noticed that in manual fan mode the upper four clicks of the fan speed do not make the fan runner any faster like it should. I would assume this is a blower motor problem or control unit problem and has nothing to do with my original post about intermittent lack of air conditioning.

 

What was the problem with the intermittent cold air? I seem to be having the same issue. Thank you for a response.

 

Thanks for the reminder...I should have come back and given an update.

It appears the problem was the relay associated with the A/C system. About six months ago I went into the fuse/relay box in the engine compartment and switched the A/C relay with the fog lights relay since they are the exact same. I halfway expected the fog lights to operate in an intermittent way which would have verified my hypothesis but they seemed to continue to function as normal. The A/C had been intermittent before the relay swap and therefore to verify the fix I would have to play the wait-N-see game. Well, in Florida the weather starts to cool in December so A/C usage was more limited and I had to wait until March for it to warm up.

Well, we are almost to July and I can report that the A/C intermittent issue has not reappeared therefore my conclusion is that the relay was the issue. I have no idea if the fog lights started to act up but since the relays are probably factory original I would say it's probably a good idea to put in new ones.

See if you can't do a swap like I did and keep your fingers crossed. Let us know if it fixes your problem.