Question: 1995 Chevy Lumina, the left engine fan comes on around 200deg, where it > supposed to. The right one i’ve never seen come on. Are they both > supposed to come on at the same time? TIA The other fan probably comes on when the A/C is on to push air through the condensor. You have air, right?

Answer: They’re actuall names are the engine cooling fan (the big one) and the auxillary cooling fan. Mainly, the only time you will get the second one to come on is when the A/C is on and the head pressure exceeds 250 psi. The second fan will also come on when the engine coolant exceeds 240 degrees. You must live in a moderate to cool climate. Down here in Texas in the summer my 92 Lumina when the air is on kicks both fans on regularly. If I’m not mistaken, when you turn the key to on, both fans should come on, this is one of the system tests. Secondary fans are used when engine temps go even higher (sometimes) but are used primarily to control the pressure in the high side of the a/c system. Some sensors and switches monitor high side pressure or temperature and turn the fan on when it rises above a preset limit. For the record some older GM systems did turn the fans on during the diagnostic check but not just with key on. This enables actuators for testing purposes. Oh yeah, now I remember that part, you had to have the diagnostic module plugged in (or the pins jumped), thanks for pointing that out.

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