Can I install a toggle switch in series with the  ac high pressure switch to turn cooling fan on manually on 1989 C4 .does it make a difference which wire I install it on. It would do the same thing as disconnecting wire. And damage on problem with computer?

Installing a switch in series with the high pressure switch will not turn on the radiator cooling fan.   A switch in that location will prevent the a/c from working.

Does your fans not kick ON when the A/C is on?

fan comes on when ac is  on .Trying to bring fan on manually early on hot days  when ac is off  I thought switch opens on high pressure and toggle switch would simulate this.

You obviously need a copy of the FSM (Factory Service/Shop Manual) for your '89.   I don't know the control electronics for your '89, but I do know that the "high pressure" switch is a safety switch, and is only actuated if the head pressure in your a/c system gets too high (about 400 psi) due to some malfunction.  If there is a malfunction, the "high pressure" switch will open, which will disengage the clutch of the compressor, effectively shutting off the a/c.   A switch in series with this circuit will prevent your compressor clutch from actuating.

I will look at the manual .  I'm a retired hvac mechanic I may be referring to a high pressure fan cycling switch . I thought that switch cycled fan . Thanks 

Checked manual .It's the  ac coolant fan switch that  closes at 240 psi  open 190 psi. If I jumper this switch with a toggle switch I should be able to turn fan on manually at any time. I had it backwards. has anyone tried this. I want to bring fan on before 226 deg.  

I live in south Louisiana, and I like having my fans kick on sooner during our furnace months (most of the year).

Are you looking at a genuine FSM (Factory Shop/Service Manual) for your '89 Corvette?  Those are some strange numbers.   What refrigerant are you using in your car?

If you're using R134A, and the ambient temperature is about 75* F., you should have your system pressure cycling at a low side pressure of 35-40 psi, and your hi side at 150-170 psi.   You should never see the 190-240 psi you have referenced.   Am I misunderstanding something?

Control of your radiator fan is a separate subject.  I believe the '89 Corvette fan turn-on temp is controlled by the ECM.  Your ECM programming can be changed to lower the turn-on temperature of your radiator fan.   This will allow the fan to operate at the lower temperature, regardless of whether your a/c is on or off!  I believe your radiator fan should actuate any time your ac is operational, regardless of the coolant temperature.

The engineers at GM considered the turn-on temperature of your radiator fan to be good at 226* F.

Here's a picture of the cycling switch for your ac.  It is normally called the "low pressure" cycling switch.  If you disconnect this switch and jumper across the terminals of the connector, your compressor clutch should actuate.

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I've done a little more research on the '89 a/c control circuit, and if I've figured it right, it seems the system is designed to turn on the radiator fan only if the a/c head pressure goes that high, which would be an unusual situation! 

Since you don't have a secondary fan in front of your a/c condenser, you don't have a coolant temp. switch (CTS) in the threaded port in your LH head, between cyl. 1 & 3.   That would be the place to install a CTS that's calibrated to the lower engine temp that you're looking for.  The radiator fan relay is located on the LH fender shield, under your master cylinder.   If you ground the control wire for that relay (I think it's the green wire), your radiator fan should come on automatically, without having to worry about a manual toggle switch!

You're probably aware that the sensor in the RH head at 6 & 8 is for your temperature gauge.





|UPDATED|4/16/2018 12:20:09 PM (AZT)|/UPDATED|