Rep Power: 453

Well I am asking on what everyones opinions are on this problem my best friend is having with her 1998 Ford mustang's AC system.

Here is her complaint, and I verified it., kinda.

Anyway, she was complaining that sometimes her AC was blowing cold air and sometimes it would blow warm air. Now when i turned it on, it was blowing semi cold air, but I was possible thinking she might have a condensor fan problem on that. But I didnt see the condensor fan, just a radiator fan. But I didnt look long enough. I was also getting line temps and couldnt remember if the line going to the accumulator, and the line coming off of it going to the compressor were supposed to be the same temps. The line from the evaporator going to it was warm, and the line coming out of it to the compressor was cold when the clutch engaged.

Now the main thing with this is when she turns on her AC to max cold, as soon as the compressor clutch engages, the cars idle starts to jump around and the car sounds like it wants to die. But when the clutch disengages, everything is fine untill it engages again. My feeling is she might have a compressor problem. like the reed valves are failing.

what do you all think?

 
Rep Power: 812

I think you're right. Have you tried driving the car for 20mins+ at constant freeway speed to see what happens with the AC on? She just may have forgotten to use it during the winter and the lubricant seized up or something.

 
Rep Power: 453

See I havent driven it. She is picky, while I had the car on with the AC on, she was getting all nervous cause it sounded like the car wanted to die.

But I still think it is a compressor problem.

 
Rep Power: 453

anyone else have any ideas?

 
Rep Power: 0

I don't think there is anything wrong with the compressor. It sounds like the a/c is working as it should. However, check to see if the idle air control valve (or idle speed motor) is faulty. What is supposed to happen is the idle air control valve is supposed to step up the idle when the a/c compressor is engaged due to the increased engine load. If this does not happen, you will get a rough idle. You will need to hook up a diagnostic tool to it to see if it is doing this. You can try to test it by doing this. Turn on the a/c such that it idles rough as you described before. Step down on the gas gently to increase the idle speed. See if that smooths out the idle. If so, I'd be suspicious of the idle air control valve.

 
Rep Power: 453

I will also check that. But the reason why I say I thought it was the compressor was because when the compressor engages, the AC blows warm air out, but when it disengages, cold air will come out. It is an on and off ordeal. And at the same time, when it engages, the car starts to bog down. She can use the AC, but it bogs the car down.


Also can I test the idle air control by turning on the heat full blast and with all accessories on and see if it does the same thing?

 
Rep Power: 0

Turning on all accessories doesn't produce a huge load like an a/c compressor engaging. It should increase the idle speed but you wouldn't notice an idle problem if the idle air control wasn't working. Turning the heat on full does nothing since all that does is open up a valve on the heater core. Compressors usually have a bearing, clutch, or shaft seal failure. When any of those die it is very obvious. A bearing failure will cause compressor noise/squeal or totally seize the pulley. A clutch failure would result in no compressor engagement. A seal failure will also result in no comperssor engagement due to the fact the refrigerant leaking out and it triggers the low pressure cutoff to protect the compressor.