C4TOMCAT

Hello all

My 94 coupe/6 speed had the opti/H2O pump go out in Dec and just got it back together but I had to open the HVAC lines so the charge is gone and I do not have time to recharge till later.

I am taking the car to the track this weekend and need to be able to run the passenger side fan but with the refrigerant charge out of it the fan cycling switch (three prong on the liquid high pressure line near the evap housing) holds the circuit open. this is the fan that cycles to maintain condenser head pressure.

I am not sure of the wiring circuit for closing so can someone who knows tell me which wire colors to bypass together to allow the fan circuit to run when I put the panel to a/c so the fan will operate. I have the compressor disconnected and the low pressure switch bypassed as well. just need the high pressure one in order to get the fan to work.(I hope)

The colors of wire are black, red, and either its gray or a dirty white.
I am sure the PCM grounds out to cause it to operate but don't want to cause more problems by hit or miss on trying it.

thanks in advance for any assistance you can give.
Tom

SunCr

Switch is a 3 wire thermistor with a 5 volt reference from the ECM. Red/Black is usually the return (the other is ground) and as the pressure increases so does the voltage. Each volt returned is about 100 psi and most of these systems try to maintain a high side of about 200 psi, so the ECM is going to be clicking on the main fan somewhat below this; ie, 2 volts; and the secondary, somewhat above it - (again 2 volts). It might be easier to simply tap into the ground side of the fan relays with a manual switch, but connecting the signal (5 volts) to the return should crank them on. That usually generates a high pressure code and I don't know if that might also cause it to run on backup, but if you get a Check Engine or Check Gages Light, might want to stay with some sort of switch.