Questions and Answers
LHS Cooling Fans
Q. Hello Vince, I am very automotive savvy and am having a weird problem. I have a 94 Chrysler LHS. It has a 3.5l V6 with air and all the trimmings. When we start it cold, both of the cooling fans come on (yes we have 2). They continue to run constantly until you turn the key off.
My mechanic friend hooked his Snap On computer device to it and was able to manually cycle the fans off and on. This tells me that the fans, relays, the wiring to them and the outputs from the computer are all working. This makes me want to look at the inputs to the computer to see if there is a condition there that would make the computer think they should be on.
We looked at the engine temperature input which at the time read low or cold. We made sure that the climate control was turned off. Do you know what criteria the computer uses to turn on the fans? There must be something in the program that says IF (?) or (?) or (?) THEN FAN(S) ON right? We're taking it to a dealer service department as a last resort. Any ideas?
Dave
A. Radiator fan control is accomplished in two ways. A pressure transducer on the compressor discharge line sends a signal to the powertrain control module (PCM) which will activate the fans. The fans are also turned on by a coolant temperature sensor, which sends a message to the engine controller. The engine controller then sends a signal to the fan relay which in turn switches the coolant fans on. Fans will not run during cranking until engine starts, no matter what coolant temperature is.
Another thing that would cause the fans to kick on is a cooling system that has air in it. If you change the coolant and don't bleed the system, you will get the same symptoms.
To bleed the cooling system attach one end of a ¼"ID clear hose that is 48 inches long to bleed screw on thermostat housing. Route the hose away from accessory drive belts and cooling fan and place into a clean suitable container. Open the bleed screw. Slowly fill coolant pressure bottle until a steady stream of coolant flows from hose. Gently squeeze upper radiator hose until all air is removed from system. Close bleed valve and continue filling to top of coolant pressure bottle.
I'd give that a shot and see what happens.
Additional Information provided courtesy of ALLDATA
