PCM A/C Fan question
01-06-2007, 09:21 PM
#1
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PCM A/C Fan question When there is an A/C request to the LS1 PCM does it automatically turn on one or both of the fan relay outputs?
I am working on an LS1 RX-7 that will have A/C from/controlled by the LS1 computer. I am going to run a single dual speed fan, and I just need to know if the PCM kicks the fan relay on when the A/c comes on or not.
If it does, then I am set. If it doesn't, I am going to have to work an extra relay trigger in for the fan.
Please let me know as I am working through this part of the wiring now.
Thanks
I am working on an LS1 RX-7 that will have A/C from/controlled by the LS1 computer. I am going to run a single dual speed fan, and I just need to know if the PCM kicks the fan relay on when the A/c comes on or not.
If it does, then I am set. If it doesn't, I am going to have to work an extra relay trigger in for the fan.
Please let me know as I am working through this part of the wiring now.
Thanks
01-07-2007, 12:05 AM
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I have taken a look at the LS1 fan diagram and it doesnt make any mention of how A/C ties into the fans. I assume since the PCM trigger wires are all that go to the relays it must turn the fans on for the A/C??
01-07-2007, 11:34 AM
#3
This is from the GM service manual. It might help.
LS1
The PCM commands low speed fans on under the following conditions:
Engine coolant temperature exceeds approximately 108°C (226°F).
When A/C is requested and the ambient temperature is greater than 10°C (50°F).
A/C refrigerant pressure exceeds 1482 kPa (215 psi).
After the vehicle is shut off if the engine coolant temperature at key-off is greater than 113°C (235°F) and system voltage is more than 12 volts. The fans will stay on for approximately 150 seconds.
The PCM commands High Speed Fans on under the following conditions:
Engine coolant temperature reaches 112°C (234°F).
A/C refrigerant pressure exceeds 1710 kPa (248 psi).
When certain DTCs set.
LS1
The PCM commands low speed fans on under the following conditions:
Engine coolant temperature exceeds approximately 108°C (226°F).
When A/C is requested and the ambient temperature is greater than 10°C (50°F).
A/C refrigerant pressure exceeds 1482 kPa (215 psi).
After the vehicle is shut off if the engine coolant temperature at key-off is greater than 113°C (235°F) and system voltage is more than 12 volts. The fans will stay on for approximately 150 seconds.
The PCM commands High Speed Fans on under the following conditions:
Engine coolant temperature reaches 112°C (234°F).
A/C refrigerant pressure exceeds 1710 kPa (248 psi).
When certain DTCs set.
01-07-2007, 11:40 AM
#4
What kind of A/C are you using? If it is an aftermarket like Vintage Air or Hot Rod Air, they recommend a trinary pressure switch to control the A/C triggered fans. That way the fans only come on when the pressure exceeds a certan setting. So, if you are cruising down the highway at 70 with the AC on, there should be sufficient air flow over the condensor to cool it and the fans won't come on then. That controls them independent of the PCM and just relies on the needs of the A/C system
If you are using an aftermarket system, you may wnat to contact them for their advice.
Pat
If you are using an aftermarket system, you may wnat to contact them for their advice.
Pat
Last edited by Stu Cool; 01-07-2007 at 01:04 PM.
