I just added a 1995 5.7 6p Conv Trans Am to my stable. 36k on it, like new in and out. One that I saw and thought I have to get this, to damn nice to pass up.
I have noticed with the AC that it will blow ice cold for a bit (sorta normal) but then for a few seconds it will get a little warm (not hot) then back to nice and cold. This car I believe has non of that BLEND door crap on it. It does it on recycle or normal What could be causing this? Low refrig so the compressor is cycling a little????

 

brgjag, odds are, you are looking at a sticky thermostatic control valve. In short, this valve bypasses some of the freon from the discharge back to the suction of the compressor to keep the freon from getting too cold and therefore freezing up the condenser. So, what you are seeing is that the system is seeing the freon getting too cold and therefore it tries to bypass some of the freon. But, because it is sticking, the freon keeps getting colder and colder and eventually it will reach a point where the valve will free up and move. As the freon is getting colder and colder, this is the cooling effect that you are seeing. Once things shift, a lot of the freon is getting bypassed and therefore the condenser gets very little freon and therefore the air warms up. Now the freon has to get essentially too hot to finally make the thermostatic control valve work again.

The only other possibility that I can think of is you have blockage in the system and the pressure is building up on the discharge of the compressor and once it reaches a high enough pressure, there is a switch that will turn the compressor off and let the pressure come back down. But, this should be associated with poor cooling all the way around with the air going from warm to slightly cooled and back to warm.

 

Chance that this will fix itself?

 

brgjag, normally once you reach this point, it is only going to get worse, not better.

 

Hum. It stays ice cold for 22 seconds then goes warm (not hot, just a little warmer then cooold) for about 10, same cycle. Will I hurt it to allow it to keep doing this, though the a/c season is about done here.

 

You asked if the "compressor is cycling"...You tell us...While it's sitting in your driveway with A/C on, fan on full speed, have someone rev it to about 2000 RPM and hold that for a minute.. if the compressor kicks in and out at about the rate your temp is changing according to your description, then I'd guess you have a low charge...If it stays engaged then what thermo said about a blockage could be the problem...need to know this first about compressor action

 

HUH?..you mean Evaporator and what you are referring to is hot gas bypass for lightly loaded evaporators.....I don't think auto A/C units have such a set up...I never heard of any at least in this year for cars, unless it's a Rolls., but I could be wrong.


PS..FREON is a trade name for DuPont..The product is referred to as REFRIGERANT in the industry.

 

So do this with the AC on FULL BLAST, MAX, then have someone hold it at 2k and see if the compressor clutch shuts off at the same intervals I am seeing the change in temp?
I have to say I have never had a car where it does this due to low Freon. Either they worked and were cold or the pressure was such that that the clutch never engaged.

 

No engagement at all means a totally flat system..compressor cycling, means there's still enough refrigerant to start but eventually sucks down to a low pressure on the evaporator side to open the low pressure switch, then during the off cycle pressure builds again to close the switch and the compressor starts again..I've seen this dozens of times......Did you try it yet?...Not saying this is absolutely the problem, but it's somewhere to start analyzing the system.

 

I am at work. I will try it tonight at home. Thanks for the tips!

 

This is a low mile car that has sat A LOT so I bet she is running a little low.

 

Makes sense then that it has just lost some charge over the years...they like to be run a little, even in the winter..the A/C I mean.

 

Yea I have always run mine in times when tit is needed, just run it for a bit to keep it in working order.

 

Drove it on lunch, about 6 min of run time then another 20 min home, stayed nice and cold.

 

Another thing occured to me..If this has a Thermostatic Expansion Valve (TXV), which regulates the flow of refrigerant into the evaporator (the part that cools the cabin air...The condensor is in the front of the radiator)..If it had been setting for so long as you said, it might be sluggish and working erratically...perhaps with time and use it will free up and regulate refrigerant flow better, maintaining a more constant temp control across the evaporator....work it for a few more days, it may straighten out on it's own....I hope.

 

I don't think it is low. I think either it has a malfunctioning part or it just needs its legs ran a little.

 

Agreed..By what you've told me, the charge seems adiquate....Didn't you also say that it seemed to run good after the last time you drove it?...Sounds like it's settling in now after sitting for so long.

 

I have had a few times over the last 4 or 5 drives where it did not do this. Perhaps this one is just due to not much usage and needed to be ran a few times to get the juices flowing again.