Electrical High Speed Radiator Fan not coming on with AC on

DRRummel

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Jun 11, 2007
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My car overheats when I use the AC and I am in traffic. The car has a mild 302 with aluminum heads making 297 RWHP. Stock cooling system. I believe I have 192 degree thermostat installed.
What I have done so far:
1. Grounded pin 17 on CCRM. High speed fan turns on.
2. Traced CCRM pin 17 to PCM, pin 32. Grounding PCM pin 32 and the high speed fan turns on.
3. Used an ODBI tester. No engine error codes. It did report a CMOS(?) error. I ASSUME that us because of the SCT chip.
4. ODB1 engine self test can run the the low speed and then high speed fan.
5. ECT disconnect, high speed fan runs.
6. Jumper ECT connector, high speed fan runs.
7. Engine warms up to about 180 degree, ECT connected, the low speed fan starts.
8. Turn on AC max, low speed fan continues to run.

The AC is on and blowing cold air. So I figure the PCM had engaged the AC compressor clutch. When turning on the AC the engine RPMs are raised by the PCM. Because of the aluminum heads I have not let the engine reach 226 degrees to see if the ECT will trigger the the high speed fan. What inputs does the PCM need to turn on the high speed fan when the AC is on?
 
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HISSIN50

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Nov 29, 1999
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Your high-speed fan should come on with the AC, that seems to be your issue. The degree of solution depends how ambitious you are. You could try and figure out what is wonky or simply come up with a work-around. To do the former would be a real hassle, and not something most people would want to do (the chip/tune throws another wildcard into the mix, as well).

Do you see a circuit breaker inline on the fan wiring? Just curious.
It looks like the tuner lowered your low-speed fan threshold. Did they lower high speed as well? Just curious again.

Since low speed functions when you need it, you could do some rewiring of the load side of the fan circuit. You'd switch the low-speed load input into the fan motor over to the high-speed fan terminal. So in all the situations currently when low comes on (they seem appropriate if I read you correctly), after the rewire, high would be coming on. You could cut up the OEM fan wiring, but I would not. I would create a jumper harness, plugging into the now-unplugged fan pigtail and connecting to the fan motor itself. The jumper wires only need be a couple of inches long. Ground to ground, low speed from the pigtail connecting to high speed on the fan motor. Standard spade connectors fit the factory terminals.

Another option would be to use a stand-alone fan controller. This could be a cheapo parts store version or something more luxurious like a Delta Controller.

Best of luck.
 

DRRummel

New Member
Jun 11, 2007
6
0
1
54
Baltimore, Md.
Your high-speed fan should come on with the AC, that seems to be your issue. The degree of solution depends how ambitious you are. You could try and figure out what is wonky or simply come up with a work-around. To do the former would be a real hassle, and not something most people would want to do (the chip/tune throws another wildcard into the mix, as well).

Do you see a circuit breaker inline on the fan wiring? Just curious.
It looks like the tuner lowered your low-speed fan threshold. Did they lower high speed as well? Just curious again.

Since low speed functions when you need it, you could do some rewiring of the load side of the fan circuit. You'd switch the low-speed load input into the fan motor over to the high-speed fan terminal. So in all the situations currently when low comes on (they seem appropriate if I read you correctly), after the rewire, high would be coming on. You could cut up the OEM fan wiring, but I would not. I would create a jumper harness, plugging into the now-unplugged fan pigtail and connecting to the fan motor itself. The jumper wires only need be a couple of inches long. Ground to ground, low speed from the pigtail connecting to high speed on the fan motor. Standard spade connectors fit the factory terminals.

Another option would be to use a stand-alone fan controller. This could be a cheapo parts store version or something more luxurious like a Delta Controller.

Best of luck.
I swapped a stock computer into the car. No chip in the swapped PCM. Again, not high speed fan with AC on.
I checked with the Tuner on the fan temp trigger temperatures. I will get an answer with he returns from vacation.
I don't have the circuit breaker on my fan.
Using the DC Controls setup is the solution I am looking at IF I cant resolve the AC / high speed fan issue.

Any suggestions on perusing the "real hassle, and not something most people would want to do" process of tracking down the AC triggers to the PCM for high speed fan operation?
 

HISSIN50

"How long does it take to get help in here?
SN Certified Technician
Nov 29, 1999
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I swapped a stock computer into the car. No chip in the swapped PCM. Again, not high speed fan with AC on.
I checked with the Tuner on the fan temp trigger temperatures. I will get an answer with he returns from vacation.
I don't have the circuit breaker on my fan.
Using the DC Controls setup is the solution I am looking at IF I cant resolve the AC / high speed fan issue.

Any suggestions on perusing the "real hassle, and not something most people would want to do" process of tracking down the AC triggers to the PCM for high speed fan operation?
You don't need to resolve anything to use the DC Controller. It's a stand-alone system (fox III's, which had no electric fan, use them all the time).

For tracking down the actual issue, it would be personalized circuit tracing. I've seen your same issue once before, and a different computer and CCRM did not change anything. You'd start tracing the control side of the fan circuits backwards from the CCRM. It's something I have not thought out, you'd look at schematics and fly by the seat of your testing pants. In the end, you do all that to try for the privilege of using the stock fan control (when you could just switch the low fan output to the high side of the fan motor itself instead, and have the same end result). Not worth it, IMHO. Either do the low to high fan wiring cross, or contact Brian, get the controller, and don't look back.
 

DRRummel

New Member
Jun 11, 2007
6
0
1
54
Baltimore, Md.
You don't need to resolve anything to use the DC Controller. It's a stand-alone system (fox III's, which had no electric fan, use them all the time).

For tracking down the actual issue, it would be personalized circuit tracing. I've seen your same issue once before, and a different computer and CCRM did not change anything. You'd start tracing the control side of the fan circuits backwards from the CCRM. It's something I have not thought out, you'd look at schematics and fly by the seat of your testing pants. In the end, you do all that to try for the privilege of using the stock fan control (when you could just switch the low fan output to the high side of the fan motor itself instead, and have the same end result). Not worth it, IMHO. Either do the low to high fan wiring cross, or contact Brian, get the controller, and don't look back.
The things we do to keep it looking stock...
I'll take a second look at the ccrm. But I thought the interaction between the ccrm and AC was strictly the relay. I figured it would be circuitry at the PCM. High-pressure cut offs is the only circuit I seen so far. I know there's got to be more. Too many pins. I hope somebody else done this before me. Off to the service manual and see if I can figure out what these abbreviations mean. Thanks for your help.
 

HISSIN50

"How long does it take to get help in here?
SN Certified Technician
Nov 29, 1999
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I understand and applaud the desire to keep it looking stock but this issue is a pain to figure out. It's just not worth it, IMHO. If you're willing to cut your fan plug wires, you could switch the low and high speed wires (cut, solder, re-loom). That would in essence solve the issue if I understand your car's issues correctly, and no one could see any modifications to the wiring since it's loomed.

In case any of this helps:

http://diagrams.hissind.com/?s=CCRM

The Dc Controller is so much better than the stock controls that it's worth the hassle of hiding the wiring and controller for it (you could do a stealthy install where it's all but imperceptible that there's an aftermarket controller. The only thing you can't hide is the radiator probe, but it's tiny and goes near the bottom of the radiator so it's hard to notice anyways).
 
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