AC gets hot when i stop at stoplight

tisha22 · #1 06-09-2016, 03:50 PM

I have a 2004 Pontiac Grand Am, it has a V6. I live in AZ, so right now its like 110 outside and my ac will work fine when i am driving but when i stop at a stoplight it starts blowing hot but when I start driving again it takes about a minute and then it will blow cold again and it does this same thing at every stoplight, but if the car is just idling in my yard with the ac on it blows cold it doesn't do this, I thought maybe it was low on freon and bought a can of ac pro with a guage and when i checked the pressure it went into the red so it says not to add any, and contact a mechanic. But I want to have some kind of idea what may be wrong with it first, I replaced the ac compresser 2 years ago. A couple of days ago I replaced all the radiator hoses and the radiator and the coolant tank and of course added the right amount of dexcool. The car is not getting hot, the problem is just with the ac does anyone have any ideas?

brcidd · #2 06-09-2016, 04:23 PM

Is cooling fan running with a/c requested? Car not getting hot is not a good indicator of cooling fan operation-- engine coolant takes about 20 minutes to "get hot" without a cooling fan- whereas a/c needs a cooling fan pronto.

gmtech1 · #3 06-09-2016, 04:35 PM

As stated above, check that the cooling fans are running with the a/c on in park.

tisha22 · #4 06-09-2016, 05:03 PM

Both the fans come on with the ac on and its in park..

Stealthee · #5 06-09-2016, 06:42 PM

Fan operation has nothing to do with ac operation other than the second fan kicks on to assist in keeping the engine cool. If neither fan kicked on the ac should still be cold since engine ac is a sealed system separate of the engine coolant, unlike coolant affecting heat.

Some newer cars will disengage the ac clutch if the car overheats as a precaution though. It doesn't sound like the op is overheating though.

gmtech1 · #6 06-09-2016, 07:45 PM

Quote:

Originally Posted by Stealthee

Fan operation has nothing to do with ac operation other than the second fan kicks on to assist in keeping the engine cool. If neither fan kicked on the ac should still be cold since engine ac is a sealed system separate of the engine coolant, unlike coolant affecting heat.

Some newer cars will disengage the ac clutch if the car overheats as a precaution though. It doesn't sound like the op is overheating though.

I have to disagree. Air flow over the condenser is critical to keep a/c pressures in check. Regardless, she stated that the fans are working.

brcidd · #7 06-09-2016, 10:30 PM

Anyone who does a/c work will tell you- the compressor cycles off high pressure cut-outs (with high ambient) whenever a cooling fan(s) are inop and car is not moving.

The speed of compressor slows with engine speed. suction pressure will rise, and cause poor cooling at idle- so to test OP's issues, hold rpm to about 1700 for 5 minutes and see if cooling is maintained when car is not moving.

tisha22 · #8 06-09-2016, 10:42 PM

Hi I am sorry please excuse my dumbness, how do I hold the car at 1700 rpm's?

brcidd · #9 06-10-2016, 09:18 AM

Sit in car- have engine and a/c running- keep tranny in park, push on gas pedal, if no tachometer, just hold it slightly above idle, (no reason to over rev engine) for a few minutes, see if cooling is maintained- or is the same as when cruising.

xeroinfinity · #10 08-18-2016, 04:27 PM

Welcome to AF tisha22 .

this is pretty normal for an older automobile. Works when the engine is above 1200 rpms, car moving or Not !

i wouldnt always trust those gauges on the AC refill from the autopart stores.

Since you had the compressor replaced i'd say they didnt pull enough vacuum so it might not be filling up with enough refrigerant to maintain cold under 1200 rpms.

Also check the AC radiator in front, if its really clogged with debri bugs n stuff that might keep it from getting cold.

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