AC Charging Pressures
Melting Slicks
Joined: May 2002
Posts: 2,717
Likes: 121
From: Sulphur LA
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
do a member search for zwede and than pick his screen name and go to his web page than go to his 71 vette page and pick the AC link. there is alot of good info. The suction pressure is dependent on the ambient temp, air flow and the condition of the A/C system. Generally the suction pressure should be in the area of 35 to 45 PSI at idle with the fan on high, the A/C in max and the doors and windows closed. There are many variables to consider when charging an A/C system. Hope this helps
Neal
Neal
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
The late C3 has a cycling clutch compressor so it is quite different compared to earlier models. You will see the low side slowly drop until the compressor turns off. Pressure goes back up and compressor kicks on again and cycle repeats. The length of the cycle varies with ambient temp & humidity. You can tell that the system is undercharged if the cycle is fast. The compressor should be on for atleast 40-50 seconds at a time. If it is only on for 5 seconds or so it is low. Over charged can be detected by the compressor not turning off at all. But keep in mind that on a really hot day and especially at idle even a properly charged system may not turn the compressor off.
