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06 PT Cruiser.... trouble shooting problem with fans not operating. Have bypassed the relays and both hi/lo speed fans work. At the harness connector leading to the relays, I get no energizer signal to the relays, with A/C on and engine at operating temperature. This leads me to believe that it could be a PCM issue, as I believe the ECT sensor only has to do with low speed fan operation for engine cooling, and the high speed fan should come on whenever the compressor is running.

Is this correct...??

thanks for the input.
 

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Welcome to Allpar. Do you have fault codes and a lit 'ck eng' light? Does the vehicle overheat when sitting?
Is the A/C compressor clutch actually engaging?
There is a refrigerant pressure transducer in the high-side refrigerant line that the PCM uses as an input to determine the need for cooling fans and compressor operation.
It sends that message over the bus to the TIPM (Totally Integrated Power Module-a 'smart' fuse/relay box) which which actually controls the fan and A/C clutch operation. It may select either fan as to the amount of cooling needed. Going at highway speeds with air blowing through the condenser and radiator, these fans may not need to run.
It may not turn these components and may store a fault code if there is a circuit condition or other problem where it would think that turning these components on would be unsafe (i.e.- a sensed short to ground). The TIPM faults codes can't be read with a regular engine code reader or in the odometer during a fault code check. You would need a more specialized scan tool to access these codes.
Cooling fan control (terminals #7 and #22) here: imagesWLinks
A/C clutch control (terminal #7) here: imagesWLinks
 

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Discussion Starter #3
Thanks very much for the detailed info, looks like I'll have to get some more diagnostic tools for for a proper diagnosis...
 
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