I have a weird situation; my fan isn’t turning on when I turn on the MAX A/C full blast or when my car is running. The only thing that’s keeping it somewhat cool is the fluidyne radiator that I’ve just installed. When it gets 85+ degrees here in California that’s when my car starts to heat up while I’m stuck in traffic or if I put the pedal to the metal. I have done some research, so first I thought my electric fan wasn’t working so I tested the fan with a 12 volt battery and it works just fine (btw it’s a new electric fan). Then I checked all fuses and relay and their all fine. I also bought a CCRM and that wasn’t the problem. I replaced both sensors that sit on top of the crossover intake manifold (Coolant Tem sensor and Temperature Switch) and nothing. What’s weird is that when I disconnect the coolant temp sensor (this sensor is right next to the thermostat housing) the fan turns on and stays on. The Thermostat is new and is a 192 degree thermostat, could that be the problem? Do I need to change my Thermostat to 180? I’m lost please help.(FYI The 96 mustang has had the full PI swap)
Please answer all of the questions and perform all of the tests. Is the fan stock or aftermarket? If stock, did you test BOTH fan speeds (low speed and high speed)? If aftermarket, is this a two speed fan or single speed fan? Have you recently done any cooling system maintenance? Are you positive that there aren't any leaks and that all of the air has been removed from the coolant crossover? Why is that important? Because air in the cross over will make the temperature gauge read LOW. OBTW, I suspect there is a problem with your low speed fan and that your high speed fan is working. Some of the clues are in your post. When the temperature sensor is disconnected, the PCM responds by running the HS fan. This is what you report (allthough your post did not state which speed fan ran). However, the fan does NOT run when the AC is on. For the V8 models, the PCM calls for a constant low speed fan when the AC is on. Obvisously, the AC performance is suffering. Your post does not state that the motor is actually overheating. Perhaps because the HS fan is working. But by the nature of the HS fan, it runs for only a short while. OBTW, IMO, it will not help this issue to change the T-stat to a lower temperature unit. It will still run hot and the motor's temperature will vary MORE. Gas mileage will suffer as well. Recommendations. Confirm that the fan works in BOTH speeds. There is a low speed circuit breaker on the right hand engine bay. It's a smaller relay box near the right hand shock tower. This is the circuit breaker for the low speed fan. Remove the CB and test with an Ohm meter. The resistance should be very low. If not, it's bad. Turn the AC on and test for +12 volts into the empty circuit breaker connector. If no voltage is found, then the problem is up stream of the CB. If voltage is present, use a scrap piece of wire to jump the CB and confirm that the low speed fan starts. The results of the tests will determine what additional tests are needed to solve your issue.
