so i just got my ac fixed and now of course my enigine runs hotter, its the 89 L98 engine. well when i say hotter its at least 220 with the ac on i turned it off and it got up to 250. bad news. im thinking a new low temp thermostat or and a radiator flush. has anyone ever had problems like this before? any suggestions on how i can cool her down?
thanks!

Devon

 

You’re A/C condenser is in front of the radiator. You’re A/C has not been working thus the condenser has not been producing any heat. Now with the A/C working the condenser is working producing heat in front of the radiator.

The air going in the radiator is not as cool as it has been thus engine cooling is not as good as before. However the difference should be under 10* and if the engine is really over heating there might be another issue. Make sure the fans are coming on at the right times and they did not get disconnected or anything got broken during you’re A/C repair.

Did the problem happen right after the A/C repair?
A radiator flush might help but if it is clogged, that usually happens over time.
A new low temperature thermostat will not help your problem but if you existing stat is stuck or tired, a new correct replacement will help.

 

+1 on the fans. My 86' only has a single fan system, but it comes on at 226 degrees and goes off at 210 degrees. I have never seen my car exceed 230 degrees under normal circumstances.

This spring I replaced the timing belts my 95' dodge Caravan and I forgot to reconnect the radiator fans. As soon as I turned on the A/C the temp gage climbed to the red. I got off the road quick enough and realized what I had done, and reconnected the fans. No problems since then.

 

Your a/c is designed to keep the gas in the Condensor at 100 to 140 degrees - well below the thermostat - 195 degrees. At 40 mph plus coolant should be close to the thermostat (whether the a/c is on or off). If it isn't, something is wrong with air flow or since it's an '89, there's a good possibility there's a leaking head gasket. Start by comparing what you're seeing on your Display by using a scanner to view the Coolant Temp Sensor signal - should be the same or within a couple of degrees. Then check for debris between the condensor and the radiator - make sure the spoiler is in good shape - ditto the shroud - and look inside the radiator to make sure it isn't pushing a bunch of sludge.

Below 40 mph, coolant and the gas in the condensor are cooled by the Main Fan. With the a/c on, the ECM grounds the Fan Relay when the high side reaches about 220 psi (and it will reach this number within seconds of startup when it's 70 or better regardless of coolant temp) and it keeps it grounded until the air reduces that pressure to something around 190 psi (again regardless of Coolant Temp). Coolant temps will be 10 to 15 degrees less at low speed and idle with the a/c on - the fan comes on sooner and stays on longer. Most cars (including your Vette) with a correct charge and a clean cooling system will have coolant temps between 200 to 212 degrees with the a/c on.

You diagnose a/c low speed/idle with a manifold gage set while you observe what the fan does. If it doesn't come on, the signal is from a switch on the high pressure line and it's suppose to open when the 220 psi threshold is reached signaling the ECM to drive the Main Relay. If that pressure is showing on your manifold set, disconnecting the switch simulates the open and the fan should turn on. If it does, replace the switch. If it doesn't, it's either the relay or the ECM. You can double check the ECM/Relay by grounding the Diagnostic terminal with the ignition on - that should also turn on the fan.

Should the fan come on and the high side pressure continue to rise (assuming you've verified that nothing is wrong with air flow) - it's plugged up or overcharged or you've got a mix of gas and air or a couple of refrigerants floating around the system - take it apart and start over.

 

well i can cross out the fans, the guy who had the car before me put toggle switches in ( yes to a stock vette i wish i knew why but i dont) so i just always run with the front and main fans on. my only thought is that the condenser or radiator could have debris in it??
thnx
~Dee

 

Running the fans at cruise - particularly the Pusher - can inhibit air flow. Also, if the a/c high side is cooled too much, it's going to cycle on and off which isn't going to give you the best vent temp and it's also hard on the compressor. I'd go back to what was engineered into it - the ECM does a credible job of managing the a/c system (though it would be better if it also controlled compressor engagement - that didn't happen until '90). You might also want to make sure that it's not overtaxing the alternator. If it's dropping below battery during idle, the fans will slow down and it will overheat. A worn a/c blower can eat up 25 amps on high; the fans 10 each, and it's putting out a measly 35 amps at idle. The Pusher was never intended for much of anything. GM's bulletin described problems with autocrossing and extended high altitude usage adding the Pusher as a Dealer installed option in '85. Later a Factory Option, it should rarely if ever be coming on.

Members have found debris between the Radiator and Condensor. You'll need to remove the shroud and you may want to R & R the radiator.

 

debris

Cleaned mine out 1 1/2 years ago now very seldom gets to 220*. Just in stopped traffic. Mostly stays at 190*

 

Mine did the same thing before I changed the radiator(which had a small leak). I could drive all day in stop and go traffic and never overheat until turning on the AC. It never gets anywhere near that warm now. I'd do a radiator flush and cleaning. It's surprisingly easy to remove and clean the radiator area of debris.

 

I installed a Dewitt's radiator and programmed my main fan to come on at 190 F. I also installed a low temp aux fan switch. When it's 100 F with the AC on; my temps are normal now.