AC warm when stopped, cold at HWY speed

[listenloud]

I have a 2000 LS. The AC is warm when sitting at stops and in traffic, but gets cold at highway speed. I tried adding R134a, cleaning condensor and cabin filter. None of this worked. Any ideas??

[shorod]

First verify that the cooling fan is operating properly. Maybe the fan is not coming on and therefore at slow speeds there is not sufficient airflow through the condensor, but at highway speeds there is plenty of airflow.

If the fan appears to be functioning properly, check the compressor clutch duty cycle. How many seconds is the clutch engaged as opposed to seconds off?

-Rod

[listenloud]

The cooling fan comes on and seems to be working correctly. The AC clutch stays engauged almost all the time at idle. After adding r134a the clutch seemed to cycle approximately every 15 seconds while driving. I could hear and feel the clutch cycling while driving after adding r134a. My fear is that I may cause damage by adding too much R134a???

[shorod]

If your pressure switch is working properly, the system will disengage the compressor clutch if the pressures are too high, so slightly overcharging shouldn't be an issue for damage. And, yes, overcharging the system could cause the symptoms you are describing.

This may be a good time to visit a local shop with the proper equipment and knowledge to make sure the system is properly charged.

I assume you've already checked for leaks and verified there are no obvious ones. Not due so much to the operation of the system, but rather in case the shop suggests you need a new condensor or something. Get recommendations from friends as to where they've had good luck.

-Rod

[listenloud]

I evacuated the system and recharged with the proper amount of r134a. I still have the same symptoms. I noticed today that the ac clutch does not cycle off at all. This leads me to believe the compressor is failing or possibly the expansion valve is not working properly??? While recharging I noticed both the high and low side pressure seemed to be very low at idle and the presures only reached the reccomended pressures when the engine was runnning at approximately 1500 rpm. Any ideas?