i have been asked to look at a 03 civic that has constant AC reguardless of user input

the ac active if the key is on, blower on/off, ac on/off. blend on hot/cold
not on defrost

engine fan always runs,

i tried the self diagnostics and it reported nothing.

i mostly work on GM cars and trucks, so any help would be great.

 

i found a blue/white wire that was purposely shorted to ground, now i can follow alldata and find the actual problem

 

Ordinarily the control panel pulls the wire to ground to enable A/C. The MCU detects that the wire has been grounded (assuming the pressure switch is closed) and signals the ECU to start the compressor and fans. It's a "negative logic" setup.

The pressure switch is closed at all times during normal operation. It only opens in case of overpressure (fans not working) or underpressure (refrigerant leaked out). The system does not cycle on pressure like most GM cars do. When the evaporator gets cold enough, the control panel releases the ground to stop the compressor.

 

first thing im gonna do is check pressure, wondering if some idiot has it under/over pressure and decided to force it on, or a pressure switch is not functioning and they forced it on,

what should the pressures be on the low side when it is on and when it is off?

the fans do work, they stayed on when the system was forced on

 

Normal pressures are the same as any other car. The pressure switch should be closed whenever the high side pressure is between 50 and 450 psi, which like I said before, encompasses any normal operating condition. There is no control on the low side pressure, it should be about 20-30 psi with the compressor running.

The wires at the pressure switch (both of them, since the switch would be a closed circuit) should go to ground when the A/C button is pressed and the light in the button is on. If that doesn't happen it's probably a bad control panel though it could also be the evaporator temperature sensor thermistor.