eugrides said: 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.
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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