Automotive Air Conditioning Information Forum (Archives)

Hard Driver on Thu May 12, 2011 1:43 PM

Year: 99
Make: CHEVROLET
Model: C2500
Engine Size: 350
Refrigerant Type: 134a
Ambient Temp: 85
Pressure Low: 35
Pressure High: 225
Country of Origin: United Kingdom

The ac stopped cooling on my 99 chevy truck and I discovered the highside port valve was dumping gas when I removed the cap.I replaced the valve fitting and evacuated the system.After adding two 12 oz cans of 134a I check the pressure which was 35 psi lowside and 220 highside @ about 85 f outside.The truck seems to be cooling relatively well but my gm shop manual calls for 2.25 lbs of 134a,will adding the additional 12 oz cause me to excede pressure limits or did I do something wrong.I have a basic understanding of refrig / ac [took course]but little hands on auto ac expirence.

mk378 on Thu May 12, 2011 1:51 PM

You don't want to run undercharged because the oil will not circulate properly. If putting the specified charge in ends up causing too much high side pressure, the condenser cooling needs to be investigated. Fan clutches wear out and make the fan spin too slowly.

Really people working on a stock system and charging by weight needn't look at the gauge until after the full charge is in. It leads to overthinking things.

Edited: Thu May 12, 2011 at 1:53 PM by mk378

Hard Driver on Thu May 12, 2011 2:12 PM

Thanks for your input,I assumed that I was charging by weight since the system was evacuated and I was using 12 oz cans so one more 12 oz can would be 36 oz =2.25 lbs. I will add the additional can keeping a eye on pressures and checking the things you pointed out if needed.