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Chevy A/C problem

stvdalton on Sun August 23, 2009 4:44 PM User is offlineView users profile

Year: 1999
Make: Chevy
Model: Silverado
Engine Size: 5.3L
Pressure Low: 40
Pressure High: 260
Country of Origin: United States

Hi, I'm new to this, but have heard a lot of good about this forum.
I recently bought a 1999 Chevy Z-71 from a buddy of mine. But just my luck, I have a problem.
A/c blows cold as long as I don't put it on max a/c. If I do it will last about 1-2 mins then start blowing warm air. It will work fine on max if you are just sitting in park.
But if you are driving it will start blowing warm. If it starts that, you actually have to turn the a/c completely off, wait about 3-5 mins then turn it back on, works fine just keep it on regular a/c. Had a friend check the psi on high and low side. It is about 40psi on low side and about 240-260 psi on high side. We have blown out the radiator fins and all, didn't help.
That was all for about a minth. So now it just started doing this on regualr a/c today. I have to actually turn a/c off wait a few minutes and turn it back on, blows cold for a little bit longer than it does on MAX A/C but then same thing. Freeon is full. My mechanic really don't know what to try. Compressor never shuts off when all this happens.

GM Tech on Sun August 23, 2009 5:04 PM User is offline

Freeon is full???? How do you know this? You can ony tell by extracting and weighing better way......

So is it icing up? you say compressor never shuts off? I would start by making sure the correct amount is in it-- you do this by extracting and weighing out and back in the charge. Then see how it performs---if indeed you are low on refrigerant- then you need to find the leak.....most likely a compressor belly leak....

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......

stvdalton on Sun August 23, 2009 5:22 PM User is offlineView users profile

Well I have an cheap gauge, it only measures low side psi, it reads 40psi and is in the blue range, when I rev up engine the psi there decreases but doesn't go below 35psi. Also, my mechanic friend has a/c machine that does all the vacuum down etc. stuff. He did whatever to it, says the freeon is correct amount. Like I said it mainly is doing this just on the max a/c which he says max doesn't do anything else to the compressor like make it run more or faster. It just recirculates the air inside vehicle and blow harder. I guess that is true? It only does this when driving above 45 mph. If I'm just around the neighborhood, it will blow cold, but soon as I get going on main roads it won't last long at all.

Chick on Sun August 23, 2009 7:25 PM User is offlineView users profile

Follow GM techs advice, while empty pull and check the O tube, change it if dirty and full of debris, might also want to change the cycling switch..

Email: Chick


Freedoms just another word for nothing left to lose

stvdalton on Sun August 23, 2009 11:05 PM User is offlineView users profile

Okay, I'm going to try to get a different mechanic to look at it tomorrow, maybe even dealer. But I checked psi again earlier and it is only 25psi now with outside temp 74 degrees. It was right on the line to add more freeon. So I think I have a slow leak. But it still doesn't explain my main problem even when the mechanic told me it was full of freeon, of it not working on MAX a/c like I described in my first post. It shouldn't matter should it if it was on max or normal a/c? My first mechanic said he wasn't sure what to do, so thanks for nothing. HA! But it is very weird. He did put the dye in it so if I do have a leak it will show up easier. Let you know what I can come with tomorrow hopefully.

HECAT on Mon August 24, 2009 5:44 AM User is offline

Throw the Low Pressure guage away; it is a joke. Reading low pressure is not an indication of refrigerant charge no matter what color zones are placed on the face.

If your mechanic did recover, vacuum, and recharge to factory spec; this is the only way to confirm full charge.

Does your friend you purchased the vehicle from have some system history?

The cheap gauge usually comes in a kit with "sealer", was this added?

The Accumulator and evap lines (near firewall) should frost up, if the evap is freesing up and blocking air flow.Or leaves and other junk could be blocking evaporator air flow.

Clutch gap could be too wide and releasing after some heat load.

If you are taking it to another mechanic, as Chick stated, have them change the Orific Tube. Inspecting for junk and restrictions in the screen of the old one, can tell a lot about the systems condition.


HECAT: You support the Forum when you consider for your a/c parts.


NickD on Mon August 24, 2009 7:29 AM User is offline

In a manual system the difference between Max and normal AC is a different switch position in the mode switch. Is your compressor engage in Max? Could be a dirty contact. Only other difference is the position of the recir door, it routes air from the fresh air intake in normal mode, but from the vehicle in Max or recir mode. Does the air flow change when switching between the two of them with blower at max? Recir also acts like a vacuum cleaner sucking up all kinds of debris from the interior of the vehicle. Typically the air blast will be stronger in recir mode as the path to the blower has less restriction or should have.

stvdalton on Mon August 24, 2009 7:50 AM User is offlineView users profile

stvdalton on Mon August 24, 2009 9:34 AM User is offlineView users profile

Okay guys, something else. I'm going to have truck looked at by new mechanic wed. morning. But anyways, this morning, temp outside was 55 degrees so I was little chilled, thought I would try the heat out since I've never used it. Drove about 20 mins, never blew even a little warm. Could all this be related with the a/c problem I spoke about earlier? Possibly the whole control panel? Heard it is easy to change and they have had problems with those panels. Worth checking into?

stvdalton on Tue August 25, 2009 3:59 PM User is offlineView users profile

Been thinking, of course still taking truck to different mechanic tomorrow, but thinking like maybe something is freezing up when I put truck on max. I'm told that the compressor does nothing diff. when on max, it just blows harder and recir. the air from inside truck. But thought well maybe the air coming across whatever cools the air is more cold and it freezes something up and I have to turn a/c off for about 3-5 mins. Is this possible? If so what would cause this? The o-tube clogged up?

Chick on Tue August 25, 2009 6:14 PM User is offlineView users profile

cooling colder air is not a problem, as long as the compressor cycles off when it's supposed to, check the low side pressure and see if the compressor shuts off around 24psi more or les... if it goes below say 19 to 20 psi, your cycling switch is most likely bad..

Email: Chick


Freedoms just another word for nothing left to lose

stvdalton on Tue August 25, 2009 9:10 PM User is offlineView users profile

Is the cycling switch what is possibly plugged into to canister thing on the firewall? It's kinda at the lower side of canister.
Do I have to have it discharged to change that switch? I know that when it is on max and I'm driving it until it starts blowing warmish air, we checked the psi on the low side and it was about 75psi and the high side was 260-280psi. Any thing there?

Chick on Tue August 25, 2009 10:18 PM User is offlineView users profile

If your low side is 75, it sounds like the compressor is toast, but yes, the cycling switch is on the accumulator (two wire switch) I would recover, check the O tube, change it while it's out, and then pull a deep vacuum and recharge..unless the O tube is full of debris, then it's a flush and compressor job... Hope this helps..

Email: Chick


Freedoms just another word for nothing left to lose

stvdalton on Wed August 26, 2009 2:34 PM User is offlineView users profile

I just got truck back from mechanic. They didn't really do anything except take my $70 to look at truck. They think my problem is the control panel in the dash there. More money. But what you guys think? Like I said before about the pressures going up a lot when this happens on max a/c. I wouldn't think the control panel going crazy would be able to cause the compressor pressures to go up like I mentioned in my first message.
Could the low pressure switch cause it though either?

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