A/C Fan power table pressures too high?

[JohnW]

Looking at the Fan Power ACP, it seems to be set to run the A/C at very high head pressures. R134a refrigerant typically runs at around the 700 to 900 kpa range in normal air conditioning applications however the standard PCM settings look to run this pressure much higher, probably around the 1500 kpa mark.

Running at this pressure means more engine power is required to run the compressor and also impacts on A/C cooling efficiency.

Are there other reasons why these setting are so high? The only thing I can think of is that bringing the fans on earlier for the the sake of A/C effiency might cause the engine to run too cool. Any thoughts on this one?

[Maggie]

Looking at the Fan Power ACP, it seems to be set to run the A/C at very high head pressures. R134a refrigerant typically runs at around the 700 to 900 kpa range in normal air conditioning applications however the standard PCM settings look to run this pressure much higher, probably around the 1500 kpa mark.

Running at this pressure means more engine power is required to run the compressor and also impacts on A/C cooling efficiency.

Are there other reasons why these setting are so high? The only thing I can think of is that bringing the fans on earlier for the the sake of A/C effiency might cause the engine to run too cool. Any thoughts on this one?

Hmm, Interesting...
The thermostat should keep the engine temp within bounds even if the fans were on full time.
Maybe the actual head pressure should be verified and compared to the PCM settings?

[Chevy366]

Doesn't the PCM have to reach two sets or values to run fans , 1. coolant temperature 2. AC pressure ?
And isn't there a fail safe for the AC ?
The max on mine is {G0918} 255.08 PSI .

[Maggie]

Doesn't the PCM have to reach two sets or values to run fans , 1. coolant temperature 2. AC pressure ?
And isn't there a fail safe for the AC ?
The max on mine is {G0918} 255.08 PSI .

As far as the pcm having to reach two sets of values to run the fans, it may be that if either of the two values are met the fans will turn on.

[Chevy366]

As far as the pcm having to reach two sets of values to run the fans, it may be that if either of the two values are met the fans will turn on.

That is what I was trying to say , either or has to be met , temp or pressure one or the other .
Most times A/C pressure is met first because at cold starts the temp is not sufficient enough , and A/C pressure will trigger the fans for a short period , after temp is reached I think temp triggers the fans more often than A/C pressure .

[joecar]

JohnW, welcome to the forum...