In stop n go driving you will have the fan pop off and on frequently. - Mike. You are looking to see if the PCM sends power to one or both relays to turn on the coolant fans. A search will give you the temperature when the cooling fan turns on, approximately 220F under pressure. If you have a situation with a central air conditioner fan not working and you have exhausted the troubleshooting steps outlined previously, it’s time to schedule an appointment with a certified HVAC technician. If the radiator fan is in working condition, move on to the next step. Found out the cooling fan wasn't running when the ac was on. The ECT sensor monitors the coolant temperature, and allows the fan to turn on if the coolant is too hot. I have a similar problem and cannot find my specifics after doing a lot of research and forum reading, so I hope someone here could help me. Ac wasn't blowing cold air. Then it goes to the radiator. The reason being, on most vehicles, is that the cooling fan doubles as a condenser fan. The temp between operating temp and fan is like 20 degrees apart, so yeah. The compressor clutch does not engage. If the a/c doesn't run then the cooling fan isn't needed. Problem solved. A faulty cooling fan relay can also negatively affect air conditioning (A/C) performance. Step 4 – Check the engine coolant temperature (ECT) sensor. Replaced the fan. Cooling fan wont turn on 6 Answers. If I open the panel and spin the squirrel cage a little, it immediately begins to blow air and runs the heating cycle. When the A/C is turned on, the fan moves air across the A/C condenser, thereby removing heat from the vapor refrigerant inside. Small cars typically have stacked AC and engine radiators cooled by a single fan. Poor air conditioning performance. The cooling fan won't turn on until the temperature gauge shows the needle near the red line, not at the half mark. That depends on the car. Figure 3. My thermostat signals the heater correctly and the burner ignites, but the fan doesn't always turn on. Radiator fan testing points. This should happen as the high side of the system approaches 214 psi. @johnblack I checked it while it is on cold state, but then when turn the AC ON the Radiator Fan turn on, so I let the AC ON while i drive my car, after 30mins driving if i turn the AC OFF, the RADIATOR FAN still dont work, even the Radiator Temp was hot. I noticed my cooling fan stopped working and would only come on when I had the AC on. If you use the ac it will run on low then as the engine needs cooling it will burst into high speed and back to low as needed. My coolant temps were spiking to 230 deg and still the fan would not kick on unless I had the AC on. Fan ran and ac was cold for two weeks. Temp was getting way too hot. 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