AC Not Blowing Cold

I am new to this site and searched quite a bit before posting this thread. My apologies if I missed something that would help.

I have a 97 Grand Prix GT 3800 V6 with a manual control AC system. The AC was working fine, except for blowing out the heater vents and dash at the same time, which I fixed by finding the vacuum leak under the windshield washer reservoir (the vacuum line had come loose). I stopped for a few hours and when getting back in the car, the AC was not cold anymore. I have had the system checked and was told the control panel was bad, so I replaced it. This solved nothing. The system has been re-checked, the freon level is perfect, everything turns on like it is supposed to, the clutch engages, etc....but no cold air. I have taken it back several times and spent a few hundred dollars on diagnostics, but the problem has not been solved. Here in Texas, it has been no fun driving with no AC for the past three weeks now in 100 plus heat.

I would appreciate any help/suggestions in solving this problem.

Thanks!

Welcome to AF.

If you are 100% sure the A/C is good as far as charge and the compressor is working properly then you may have a flaky temperature actuator in the HVAC system. The actuator is controlled by the temperature knob. The actuator controls a temperature valve/blend door. So check into that possibility.

How do the refrigerant lines on the firewall feel going into and out of the evaporator and around the accumulator?

Thanks for the welcome! I am going by what the shop kept telling me each time I took it in. I understand about the blend door, that is what was mentioned in justifying changing the control panel, but putting the new one on made no change. I can rotate the knob to heat and the air will instantly turn hot, don't know if that means anything.

I went out just now, started the car and let it run for a couple of minutes..I can tell no difference in temp feel between the two lines up by the firewall and then as best I could, I felt the lines before and after the accumulator, I could tell no difference in either place.

One thing I noticed just now, after turning off the car....there is almost no sound of...what I can best describe is the freon going back into the system somewhere..don't know if that makes sense or not....normally when I turn off the car, you hear that discernible hissing sound of what I assume is the freon going back to where it sits..but now I barely hear maybe one second of that hiss......this makes me wonder about a blockage in a line? Is this possible?

Sorry to be so full of questions.....

Thanks!

Were any of the lines cool to the touch. Any condensation?

Something is not right. If the compressor was working properly and the charge was proper the line from the output it to the evaporator core should be cool, also one of the lines on the accumulator. You may have a clogged orifice valve, condensor or a pressure switch not working properly.

Have you checked the high and low port readings?

No, I couldn't really feel any difference on the lines, they both felt the same to me. I didn't see any condensation at all. I haven't checked and don't have any way to check the readings myself. The shop just said the readings were where they are supposed to be, which doesn't make sense to me, now that I think about it. One thing I realize I forgot to mention earlier, before, as soon as I turned on the AC both cooling fans would come on right away at the high speed, they only come on now when the engine reaches right below 210 on the gauge.

I really appreciate your input.

Thanks.

Did the garage replace the control with a new or used unit? I agree with bnaylor, that checking the difference in pressure readings between the high and low sides would be a good way to check for a system blockage. The actuator he mentioned may not be operating it's full range. It may go towards hot, but not towards cold, so it's not eliminated as a problem. Since there is no discernable temp difference in the lines under the hood, nor any condensation forming when the a/c is on, I'd lean toward a system blockage that isn't allowing freon to circulate over the temp actuator.

The control was a new one, which was not cheap......is there a way I can see the actuator? I have been all under the dash already, tracing the vacuum lines to fix the problem of blowing out the floor and dash vents at the same time, so I know how to take all that mess out, if necessary. I have put a call to the garage to ask if they noted the specific readings......what started me thinking about a blockage was what I mentioned earlier about not hearing that hissing sound after I turn off the car.

Thanks for all the input, I really appreciate the help.

You are welcome.

Both cooling fans definitely come on with the A/C is turned on. With A/C on what determines the fan turn on to include engine temperature is system refrigerant pressure both high and low. The PCM senses this to control the compressor. It sure sounds like the compressor is not being commanded on possibly due to bad charge like under or overpressure. A flaky hi/lo pressure switch could cause your problem too. It is located by the accumulator on the driver's side.

As suggested a high and low diagnostics will help.

The owner of the shop called back, they don't remember the high and low readings. I talked to him a bit, he said to bring it back and they will check this. I am not sure if I mentioned earlier or not, but the clutch does engage on the compressor and stays on. I am wondering if there is a blockage, could this cause the pressure to not build in the proper place for the PCM to make the fans come on? With everything ya'll have told me, it sure seems to indicate that there is a blockage in they system, which again makes me question the shop, it doesn't seem like this should be that difficult.

As if this isn't enough, this last time I went out and had the car idling for a while, my low coolant light came on. As I started checking around, I noticed that I have a small leak at the upper left (drivers) side of the radiator, right at the top.......I see the telltale signs of anti-freeze seepage on that side. I think the car will sit till after labor day, this isn't how I planned to spend my holiday weekend!

Again, thanks for all the helpful info.