No high speed cooling fan.

LS04sport

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Hello,

This problem did not seem to fall into the other "cooling fan" questions when I searched. Cars is a 2004 LS 3.9. Problem is the cooling fan will not got to the high speed setting when the a/c is turned on. The fan does run but it runs at the low speed and will fluctuate slightly with coolant and ambient temperature. When the car is first started shortly after having been driven without the a/c turned on the fan will run on high for a short period of time and then settle down to the low speed. Normal for the car, or alteast as long as i have owned it which is most of its life. The DATC will not perform the self-test or check for continuous codes. Holding the off button and floor button followed by the auto button does nothing. No codes, no full lit display indicating there are no codes. Same is true with off, panel, and auto. Since the fan should go straight to high speed operation once the a/c is turned on I am wondering if the internal DATC high speed relay is shot. I notice the a/c getting warm at slow speeds or when stopped, but as soon as the car is traveling again at 35 mph or more the a/c is cold again. It is not low on freon, verified with gauges, in fact the low side tends to be higher than it should be indicating an airflow over the condenser problem. As far as I can find looking in the Ford workshop manual and the owners manual there is not an external relay for the fan. Only a fuse in the passenger kick panel. Any thoughts are much appreciated.
 
The fan is variable speed. The PCM tells the electronic controller in the fan what speed it wants via a PWM signal. There are no relays.
Getting the DATC to go into self-test mode can be very tricky. I assure you that yours will, you just need to get the timing of the button presses right.
High high-side pressure would indicate not enough air flow (or a few other problems). High low side pressure does not. High low side pressure indicates an overfilled system (too much R-13a), a bad compressor (does happen), or a bad expansion valve. You need to know what the high side pressure is. If it is low, then you probably have a bad compressor (or at least the control valve in the compressor). Low high side pressure would explain the fan not going to high speed. Been there, done that.
 

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