I have a car that came to me on referral, the complaint was that the A/C only blows cool while moving. The Customer stopped at a local auto parts store to purchase a can of refrigerant and recharge the system, when the store clerk who was assisting him hooked up the can gauge to the low side service port the gauge went to the red and the store clerk gave them my card and suggested they call me. Upon inspection of the system I found that there was 3.5% air contamination, which I initially attributed to the can tap being open when the clerk connected it to the low side port, and an extremely clogged cabin air filter, after talking to the customer they told me they had bought the car used and they had never had any service done to the a/c system. The customer purchased a new cabin air filter and I installed it. Then I recovered the refrigerant, pressure tested the system with 170 psi nitrogen for 20 minutes and there was no loss of pressure, I then vacuumed the system down to 230 microns for 15 minutes, then let it sit for 15 minutes with no loss of vacuum after which I pulled vacuum for another 15 minutes and then charged the system with 1 pound 2 ounces of refrigerant. after which the high side pressures were around 140psi and the low side was around 33 psi with an 89f ambient temperature and the vent temperature was blowing 44.3 at idle, and got down to 43 at around 1400 rpms with the windows and doors open and the a/c on max. I then checked the system again with my identifier and verified that there was no air in the system. At this time I returned the vehicle to the customer at about 9:00 am. At about 9:30 p.m. I received a text from the customer letting me know that the a/c was blowing warm again. I called and spoke with him to get the details, he said that they were sitting at the drive-in movies about 30-40 minutes with the system running and then it started to feel warm. I have a few questions that maybe the community can help me with:

1. How long will a small a/c system continue to produce cold air with the vehicle at idle and no increased air flow across the condenser? 2. If I hook my identifier up to the system and find air in the system again, how did it get in there and why didn't the pressure and vac test show it? 3. If there is air in the system again am I correct in thinking that it MOST likely entered some where on the suction side?

I am sorry for such a long post but I am trying to be as thorough as possible, thank you in advance for any help, Greg Kastner

Greg Kastner
Owner
Greg's Mobile Automotive A/C Repair
Barstow, California, USA