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?
Vette(s): Black 1979 L-82
Black 1996 LT1
Black 1999 Coupe
eugrides said: 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?
eugrides said: 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.
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.
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.
eugrides said: Checked manual. It's the ac coolant fan switch that closes at 240 psi and opens at 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'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.
Reading these numbers right from FSM. these are for the HIGH SIDE of system page 8a-31.I know these numbers are high for R 12 or 134a which I now are using. I"ll probably change thermostat to 180 deg. and change coolant sensor switch to 200 -205 deg range.Thanks for your input. No aux fan.
Vette(s): 1987 C4 convertible 350ci auto
white / red / white top
appx 18k mls
you can fairly easily connect a manual switch to jumper the coolant temp sensor which will operate if the coolant temp reaches 240F. This is positioned at the left side of the engine and operates by connecting the lead to earth, energizing the fan relay. Thus, you need to wire your manual override so that you can provide earth when desired.
I ve routed the wire to pass through the driver's side door seal to underneath the dashboard. earth connection was made using a redundant bracket next to the brake pedal mounting. didn t manage to get anything through the front bulkhead, which would have been first choice.
this installation works well and provides peace of mind, as the standard switching temperatures (240 on, 230 off) are very stressful for the engine esp the head gaskets.
wolfuser said:I've routed the wire to pass through the driver's side door seal to underneath the dashboard. earth connection was made using a redundant bracket next to the brake pedal mounting. I didn't manage to get anything through the front bulkhead, which would have been first choice.
Wolfram, your '87 is different than eugrides '89. His radiator fan is controlled by the ECM, so he's trying to be creative to bypass the ECM, rather than finding a way to re-program his ECM to lower the fan turn-on temp.
I believe your '87 wiring is like my '84. My radiator fan is also controlled by a coolant temperature switch (CTS), like your '87. I'm sure the wire thru your door gasket works, but it's a bit awkward. If I'm right about your wiring being like my '84, there is already a wire under your dashboard where you can connect your manual switch. It's a jumper between the top and bottom connectors to the left of your steering column. In my '84, it's a grn/wht wire between C110-2F and C115-7E.
Have you considered replacing your CTS with a lower temp. switch? The ACDelco D1855B works well for me.
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