2001 Tahoe cold AC while driving, warm when idle

[tremmert]

Hello,
Having some issues with my vehicle AC. I just ordered some gauged and a vacuum pump to help with the repair. Basically, my vehicle, a 2001 chevy tahoe, has good AC when I am driving down the highway. When I am at idle, it blows warm. Please look at the following link for gauge readings at idle @ 90deg outside. (I couldnt attach it to this forum because the image was too large) https://s32.postimg.org/3salmlu05/IMG_0328.jpg

I have completed the following:
Replaced the fan clutch
Had the R134a topped off at a auto shop
Replaced blower motor in the cab
Cleaned condenser and confirmed airflow across condenser

Both the front and rear have similar temperatures.

One thing I noticed is that the compressor seems to be running 100% of the time when I am at idle. I unplugged the switch on the dryer, and the compressor shut off. Once I plugged it back in, the compressor re-engaged.

Temperatures when driving on the highway are about 50-55deg while outside temperature is about 90-95deg. Idle temperatures are about 80deg.

Any thoughts as to what might be happening? My next thought was to see if there is a restriction in the orifice tube...

Tommy

[GM Tech]

Suction pressure at 80 psi while at idle is why there is little cooling-should be near 35-40psi, topping off is not the way to fix any a/c system. You must put in the system exactly what the under hood label specifies. If OT was plugged, discharge pressure would go sky high. So with that in mind, you may be overcharged by a pound or so, so have system refrigerant extracted and weighed- then evacuate, fill to factory spec. If cooling does not improve, and suction runs high- be sure pump is turning- and belt is not jumping over pulley (low mount nippondensos compressors have severe rattling, tensionor bouncing issues at idle) This is a 5.3L or 4.8L engine right? Other than that, the compressor may be worn out- how many miles....?

[tremmert]

Thanks for the reply!

This morning I had the system evacuated and weighed, and re-charged to factory spec. I cant remember off the top of my head, but I think it was like 2.7lbs. Cooling has not changed. At idle, it blows warm air, but when I'm driving, it blows cold.

I looked under the vehicle, and it appears that the belt is NOT jumping. Sounds and looks normal, except for the fact that it is engaged the entire time.

This is a 5.3L V8, with 245,000 miles. The last compressor was installed at 190,000 miles at the Chevy dealership. They also installed an "in line filter".

Any other tests I can perform to help diagnose the issue, or does it sound like I need a new compressor?

[Cusser]

This morning I had the system evacuated and weighed, and re-charged to factory spec. I cant remember off the top of my head, but I think it was like 2.7lbs. Cooling has not changed. At idle, it blows warm air, but when I'm driving, it blows cold.

Did this shop that find the refrigerant was not at 2.7 lbs, then adjusted to that? If shop had such capability, did you ask them to diagnose and fix the AC or just pull refrigerant and add the correct amount (which they apparently did)?

I'd be interested in low and high pressures at 1500 to 2000 rpm, after a few minutes of running the AC.

Any way to feel the inlet and outlet lines to the front evaporator for temperature, or to use an infra-red gun to measure those?

[acloser]

Was there ever a solution? I'm working on a 97 express van with the exact same symptoms. Low side runs around 70-75 and high side is around 200-225. Front and rear vents are similar temps. Around 55-58 driving and up to 80 idling. Ambient temp around 85. Accumulator sweats and the lines to the evaporators are warm on the high pressure side and cold on the low pressure side. I fished the system, installed 3 new compressors, new condenser, new accumulator, new orifice tube, new expansion valve, and a new fan clutch. Can't seem to figure out why my pressures are wrong even after charging the system to spec. Also the pressures at 1500 rpm go to 55 low side and 250-275 high side. With vent temps getting to maybe 68-70.