one fan runs as soon as i turn the key on until i turn it off. the other only comes on when the a/c is ran. all the fan relays according to a multimeter and a diagnostic system are functioning properly. i KNOW this is wrong. i want to fix the problem, not run toggle switches. can anyone help?

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'92 Z28,t-top,PPG jet black,5.0L TPI,Auto w/stage 2 sft. kit,
michelin pilot 245/50/ZR16 tires,polished plenum/intake,flow tech 3" exhaust,PIAA driving lights

 

Mr. Sinner,

If the fan that runs continuously is the passenger side, then I'd suspect that the coolant fan switch (bewteen #6 and #8 cylinders, above the starter) is permanently "closed", grounding the single wire connected to it (which grounds the coil side of the associated relay).

Remove this wire. If the fan stops, you've found the problem. Replace it with a cooler switch (call Summit). The factory unit turns on with too hot a temperature.

If this fan is the drivers side, the ECM controlls it (via the temperature sensor located next to the thermostat). The problem could be one of several things. Try replacing the sensor (~$30) and see if that fixes it.

Regarding the other fan that comes on with the A/C - that may or may not be normal depending upon several factors (vehicle speed, freon pressure, etc.). Does it ever stop with the A/C on? Which fan, drivers or passenger side, is it?

 

it is the driver side that always runs and the passenger side that only functions with the a/c on. the passenger fan never turns off when the a/c is on. it will only turn off when i turn off the a/c.

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'92 Z28,t-top,PPG jet black,5.0L TPI,Auto w/stage 2 sft. kit,
michelin pilot 245/50/ZR16 tires,polished plenum/intake,flow tech 3" exhaust,PIAA driving lights

 

The drivers side is controlled by the ECM. According to my 1991 manual, the ECM will turn on this fan when:

1. Coolant temperature is > 222°F.

2. The A/C control head pressure is > 232PSI and the vehicle speed is less than or equal to 40MPH. Note that the ECM will keep this fan on for about a minute after turning off the A/C, even if you turn the A/C on for just a second, the delay will occur. The delay comes from a timing circuit in the ECM.

The problem could be several things. I'd first suspect a bad temperature sensor (located near the thermostat with two wires connected to it). See what happens when you remove the two-wire connector to this sensor. If the fan stops, I'd replace this sensor. There are other ways of testing this sensor (by resistance/temperature or getting the data from the ECM), but this is probably the easiest, and if you aren't too concerned about risking about $30 for a new sensor, it may be the best/easiest.

Since the A/C pressure also turns on this fan, try disconnecting the A/C pressure switch. Does the fan stop?

The secondary, or passenger side fan should come on when:

1. The coolant fan switch, located between cylinders 6 and 8, reaches 238°F, off at 214°F (!!!) - this is from the factory, and most will probably agree is pretty hot! I replaced it with one that turns "on" at 200° and off at 185°. Summit had it (JET P/N 60600).

2. The fan A/C pressure is >232PSI - this switch is connected to two wires. (Vehicle speed will not affect this fan [via the ECM] like it does the other because the ECM is not connected to its relay - only two switches as described above control this fan relay).

This fan should not normally be on all the time with the A/C - I think. Mine will turn off when the head pressure is <232PSI. But since I put in the R134a refrigerant, it seems to stay on for quite a long time (indicating a pressure >232PSI), but I rarely use the A/C, so it's hard to say what is normal. I seem to remember this fan being off more when I had R12 in. Perhaps someone else can answer this.

FYI, I have an L.E.D. illuminate in my gauge panel (right next to the temperature gauge) for each fan when it's on, so it's easy to know when they are on or off when driving...

[This message has been edited by Stuart Moss (edited July 15, 2001).]