2002 Trailblazer bad AC in stop/go driving

[CakeBlazer]

2002 Trailblazer LTZ. During an initial drive in hot weather the AC will be fine and put out plenty of cold air but if the car is stopped and turned off for a few minutes then started again the only thing that keeps the AC cool is keeping the vehicle moving at 60+ MPH. Basically, if the engine didn't cool back down to ambient temp during the stop the drive afterwards will likely have this issue.

I've read elsewhere this is a fan clutch issue, with the fan not pushing enough outside air over the temp sensor to allow the AC compressor to turn on, but it was never clear exactly what the problem was and what exactly was required to fix it.

 

[mrrsm]

Welcome to GMT Nation...

Depending upon what your Engine Temps are at Idle... With and Without having the A/C Turned on… It sounds like you may be dealing with Two Distinct Problems:

The Cooling System:

Low Coolant Level, Bad Thermostat, Sketchy Engine Temperature Sensor, Clogged Radiator, Clogged Heat Exchanger Coil, Radiator Coils Obstructed by Plastic Bag(s) or Leaves and Dirt held in place by PAG Oil leaking out from the A/C Condenser Coil.

The HVAC System:

Low Refrigerant Charge, Poor EM Clutch Engagement, Weak Timing Belt Tensioner

Trailblazer/Envoy/Ranier HVAC Refrigerant Capacity Specifications:

REFRIGERANT R-134A
Refrigerant Charge (Standard) - 0.86 kg (1.9 lbs.)
Refrigerant Charge with Rear A/C - 1.36 kg (3.0 lbs.)

Diagnostic Tools Needed to Avoid “Guessing” or Changing Parts Unnecessarily:

BLUE TOOTH OBD2 Code Reader
Harbor Freight HVAC Automotive Manifold Gauge Kit

How to Repair and Charge the HVAC System:

 

[CakeBlazer]

Welcome to GMT Nation...

Depending upon what your Engine Temps are at Idle... With and Without having the A/C Turned on… It sounds like you may be dealing with Two Distinct Problems:

The Cooling System:

Low Coolant Level, Bad Thermostat, Sketchy Engine Temperature Sensor, Clogged Radiator, Clogged Heat Exchanger Coil, Radiator Coils Obstructed by Plastic Bag(s) or Leaves and Dirt held in place by PAG Oil leaking out from the A/C Condenser Coil.

The HVAC System:

Low Refrigerant Charge, Poor EM Clutch Engagement, Weak Timing Belt Tensioner

Trailblazer/Envoy/Ranier HVAC Refrigerant Capacity Specifications:

REFRIGERANT R-134A
Refrigerant Charge (Standard) - 0.86 kg (1.9 lbs.)
Refrigerant Charge with Rear A/C - 1.36 kg (3.0 lbs.)

Diagnostic Tools Needed to Avoid “Guessing” or Changing Parts Unnecessarily:

BLUE TOOTH OBD2 Code Reader
Harbor Freight HVAC Automotive Manifold Gauge Kit

How to Repair and Charge the HVAC System:

Thanks for the detailed info. What I had read on the issue previously was that it was a matter of low fan speed at idle causing the issue and that there was a fan clutch/PCM upgrade that forced a higher idle speed. Granted, I'm ignorant on such things so may be misunderstanding something.

I'll look through all the suggested issues and check everything out, see if I can narrow it down.

 

[Mooseman]

Although the charge level is important, in your case, the usual suspect for your EXACT issue is the fan clutch. Easy way to check it.
How to test the electro-viscous fan clutch