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I have a 2000 Chevy Cavalier Z24 and I repaired my A/C last year. After the repair, the A/C worked all summer then after the winter when I went to turn on the A/C, it stopped working again. Anyone have any ideas?  

believe it or not.. first thing is to check the trouble codes...

the AC system consists of several different systems..

the ac compressor... pulls R134A from the low pressure side of the system and compresses it into a hot high pressure gas.. where its pushed into the condenser in front of the radiator.. the air flow cools the hot high pressure gas into a warm high pressure liquid..

from there the high pressure liquid flows through a tiny opening inside the hose into the low pressure of the evaporator..  where the liquid becomes a LOW pressure gas.. this lets the molecules separate and they become COLD..   they then pick up heat from the air passing through the evaporator.. and you are getting cold air...

if you don't have the proper amount of R134A...  the pressure switch will let the computer know and the computer will not turn on the compressor..

inside the dash.. are several more systems...

the blower...

and the controls to direct air from the windshield to the dash board outlets or the floor outlets..

there are also trap doors that blend cold air from the evaporator and the heater core to get you the exact temp air you want..

so.. when you set the system to defrost..  and hot.. does it blow hot air out at the base of the windshield..

when you move the control to cold.. does it blow cold...

does the compressor turn on when you command it..  please DON'T probe the connections..

does the blower come on.

does the dash board controls switch the air from defrost to the dash to the floorboards..  

DTC 04 - Compressor Relay Short to Ground/Open
DTC 05 - Compressor Relay Short to Battery
DTC 10 - Inside Air Temperature Sensor Voltage Low
DTC 18 - LH Air Mix Door Mtr Volts Low/Open Circuit
DTC 21 - RH Air Mix Door Motor Voltage High
DTC 22 - Floor Air Mix Dr Mtr Voltage Low/Open Circuit
DTC 23 - Floor Air Mix Door Motor Voltage High
DTC 24 - Def Air Mix Door Mtr Volts Low/Open Circuit
DTC 25 - Defrost Air Mix Door Motor Voltage High
DTC 27 - Blower Motor Voltage Low or Open Circuit
DTC 28 - Air Circ. Valve Voltage Low or Open Circuit
DTC 29 - Air Circulation Valve Voltage High
DTC 30 - Heating Cut-Off Valve Volts Low or Open Circuit


and probably 100 more..




P0645 A/C Clutch Relay Control Circuit
P0646 A/C Clutch Relay Control Circuit Low
P0647 A/C Clutch Relay Control Circuit High