Been running into some problems AC on the 02 i just purchased. The seller told me he figured it was the mechanics never filling up the system after he had the duramax replaced and all it needed was a recharge, however, I'm not sure I fully believe that anymore. The system was a bit low on 134A, so I toped it off, to the pressure the recharge kit recommended I believer it was around 40psi, but I could be wrong, but I still have now cool air flowing out of the vents in the truck. For the last two days the compressor had been cycling on and off for short periods of only a second or two every twenty or thirty seconds, but now it seems to no longer activate at all. The truck is an 02 equipped with the electronic temperature controlled HVAC system.
Thanks
Tai

You have a leak somewhere in the system.

I remeasured the system pressure today and it has stayed constant to what I filled it with originally.

Compressor cycling is either low freon charge or bad low pressure switch.
Jumper the low pressure switch connector with a paperclip, and THEN convey low side pressure value for us to see. At idle, it should be around 35 and, as you raise the RPM, it should drop, but never lower than 25. If it goes below 25, then your freon charge is too low. Staying above 35-40psi, and the freon charge is too high or the condensor is blocked for airflow.
http://www.dieselplace.com/forum/showthread.php?t=170585&highlight=jumper

heymccall, thanks for the advice, one quick question you have be a bit confused, i think it was just a slight typing error, but you said never lower than 25, then in the next sentence you say never lower than 40, I think you meant higher, but i wanted to double check.

Also just to check before I add 134a as I don't want to over pressurize the system. Right now the charge is around 40 psi with the AC on but the compressor isn't running but it drops to around 10 when i jumper the switch. I need to add 134 until it stays at 35 with the compressor running/switch jumpered, right?
Thanks


Compressor cycling is either low freon charge or bad low pressure switch.
Jumper the low pressure switch connector with a paperclip, and THEN convey low side pressure value for us to see. At idle, it should be around 35 and, as you raise the RPM, it should drop, but never lower than 25. Lower than 25 and your charge is low. Never lower than, say, 40psi, and the charge is too high or the condensor is blocked for airflow.
http://www.dieselplace.com/forum/showthread.php?t=170585&highlight=jumper

heymccall, thanks for the advice, one quick question you have be a bit confused, i think it was just a slight typing error, but you said never lower than 25, then in the next sentence you say never lower than 40, I think you meant higher, but i wanted to double check.

Also just to check before I add 134a as I don't want to over pressurize the system. Right now the charge is around 40 psi with the AC on but the compressor isn't running but it drops to around 10 when i jumper the switch. I need to add 134 until it stays at 35 with the compressor running/switch jumpered, right?
Thanks

Set the dash to Max AC, highest blower setting, and then, Yes, charge until the low side number, at idle, is approx 30-35psi.