cooling fans

[Murf]

Had overheating problem in my 88. Removed my radiator and cleaned out all the leaves, paper, etc. While I had it out, checked the cooling fans to make sure they were working. Grounded A & B pins on ALDL, turned key to ON and only the primary fan would run, secondary would not. Wired secondary fan to 12 volts and fan runs ok. Changed all 3 relays and grounded A & B pins, tried again. Secondary fan still won't come on. Started car after I got everything back together and let it idle. Main fan came on at 226 degrees. Couldn't get it to 235 degrees to check secondary. Any ideas or suggestions. Thought about wiring secondary fan and installing switch to make it come on when I want, but I would prefer to have it work as it should.

Thanks,
Murf

[ChuckG]

The primary is ECM-controlled. The secondary fan is temp sensor-controlled.

I'd look to a bad sensor next.

[Murf]

Chuck, thanks for the quick reply. Understand about the sensor. Grounding A & B pins and turning ignition key to ON should make both fans run according to Haynes manual ( yes, I have FSM from GM but it makes no reference to secondary fan ). Haynes states that if one or both fans do not run, then one of the relays is bad. Replaced all 3 ( 2 were original) but secondary still won't run.

[ChuckG]

My thought then is look for a short, in the absence of any contrary information. Could be as simple as bad solder any one of many places. Guess I'd try following the wires.

Oh, and I recall some of the Corvette aftermarket shops carrying a user-controlled secondary fan switch. If I remember right, it wasn't much.

[c4c5specialist]

HI there,
NO< this is incorrect.
ONLY if the temperature gets to 235 degrees, will the fan turn on.
IT WILL NOT RUN, by grounding A to B.
ONLY PCM operated fans will run, which is your primary.
Actually, I think everything is working properly.
Allthebest, c4c5

[ChuckG]

Learning not rely on Hayes....

[Murf]

c4c5, thanks. Had car overheat in parade. Thought I had everything right, just needed confirmation. All cleaned out and ready to go now (I hope).

ChuckG, don't really like Haynes manual, but the GM Factory Service Manual makes no reference to the secondary fan at all that I could find. Thanks to both of you for your replies.

Murf

[froggy47]

Cut a piece of sturdy cardboard to cover most of the rad air intake area ahead of the a/c cond. That should get the temps up. Be careful.

[ChuckG]

I've had Hayes and Chilton's lead me a astray, but as you state, the GM service manual has some gaps.

Guess we're lucky to have so much shared wisdom here!