Coolant fan doesn't work, a/c fan does

Discovered this last year, put it off until spring, and... it's spring.

Coolant fan doesn't appear to work, while the a/c fan does. When the coolant gets hot the fan doesn't go on, so the car gets hot at idle-speed. The a/c fan does appear to work, when the a/c compressor engages, one fan goes on.

Both fans work, when hard-wired to +12v.

Looking at the '97 Venture wiring diagram, it appears the trigger comes from the engine ECU, not directly form a temp sensor. So the only wearable part that appears to be able to break would be the fan relay(s). The digram shows a #1 relay, #2 relay, and common relay.

Is this common? Are all three the same part number?

Any input welcome. Thanks!

Have the same problem with our 01 Silo, except that our A/C fan does not come on either, even when the A/C is operating. I will charge the A/C tomorrow to see if that is the reason the A/C fan isn't coming on.

I have hot wired the fans and both work. I have also replaced the coolant temp sensor, but to no avail. I'm hesitant to replace the thermostat because the upper radiator hose does get hot, i.e. is open but could also be stuck open. Too many posts everywhere of people throwing new parts at symptoms with no fix of the real problem.

Does this radiator normally push out coolant when the cap is removed on a cold start? I know it is angled down, but on all other cars I have owned it is not under positive pressure and it doesn't leak out when testing at start up.

We have owned this car since new. We hope to get 20 years out of it to justify the $21K purchase price. GM engineering, or lack of it, is starting to show its ugly head.

First- the cooling fans and a/c fans are one in the same-- no difference! Low speed is both fans on receving 6 volts each in a series circuit, and high speed is 12v to each fan in a parallel circuit- if a fans work with with a/c on- stop- your done- all is fine. When the fan(s) come on with a/c that is proof they work and will work when engine temp is high enough....so why do you think the fans do not work, by the temp guage? Engine temp must be 227 for fans to come on low speed and about 235 for high speed---yes this takes awhile sitting at idle for engine temp to get this high- watch the engine temp on a Tech II and you'll soon see that an engine can sit and idle for 20-30 minutes with no fan commanded on-227 takes awhile- the temp guage will be above half way and still no fans-- this is perfectly normal operation!! Again, if fans come on with a/c, your system is fine..The a/c has to generate 175 psi head pressure to trigger fans- if your a/c is dead or low on refrigerant- fans will not come on- they are dependent on a/c pressure. A Tech II can also command the fans on to test the circuit.

So are you guys seeing the guage in the red and coolant boiling over? If not, I'd say chances are you are trying to fix something that is not broken- see it every spring when folks notice the dash guage reading higher than what they are used to--as in winter driving--If they turn on the a/c, then guage returns to their normal reading - if a/c works.

BRCIDD, is correct concerning coolant fan operation.....

Have the same problem with our 01 Silo, except that our A/C fan does not come on either, even when the A/C is operating. I will charge the A/C tomorrow to see if that is the reason the A/C fan isn't coming on.

Your a/c fans do not come on when you turn the A/C on? But does the compressor engage when you turn the A/C on?

Is your vehicle overheating?

Again- cooling fans only come on when a/c pressure hits 175 psi--otherwise the fans would be running while driving down the road which is a waste of electrical energy..so when you are parked and a/c is on and compressor is on- there still has to be enough refrigerant in your system to produce 175 psi head pressure-- if your a/c does not cool when a/c compressor is on-- then chance are your fans will not engage either- because there is not enough refrigerant to generate adequate discharge (head) pressure....

Thanks for taking the time to respond. Yes, the engine will overheat (red zone in temp. gauge) when stationary and with the engine running due to no fans working. Radiator cap works and pressure will force coolant into overflow reservoir. When moving, needle comes down to safe level and A/C seems to blow somewhat cold air front and rear.

Tried to add refrigerant today. No go. Initially when turned on, the compressor clutch seems to kick in and low side pressure is 50-55. It then quickly turns off (at idle rpm) and pressure jumps to 110. I will be taking it a mechanic on Tuesday to fix the A/C and hopefully the fan issue. Most A/C components (compressor, condenser and accessories) were new in '06 under 5 year factory warranty replacement. GM paid out over $4K to dealers under that warranty period for many big fixes (LIMG twice, tranny rebuilt, A/C stuff, turn signal stalk, etc.)

Hard for me to believe that a non functioning A/C unit prevents all fans from working. Seems like a no fail safe design.

I am pretty good with DIY repairs, yet this vehicle has so many serious issues. Had to use a band aid plumbing repair on the condensate leaking into cabin. Living with no ABS. Front driver power window is partially failing. Sliding door power lock buzzes, but mostly works every time. Control arm bushings need to be replaced. IAC valve? sometimes causes controlled runaway acceleration. ...

Most people would consider our van a lemon. I will try to keep it going for $ sake.

Hard for me to believe that a non functioning A/C unit prevents all fans from working. Seems like a no fail safe design.

.

WRONG- that was never said--fans will work if engine temp is above 227 and a/c is on or off- they are independent events....

Also with cooling fans inop your a/c discharge pressure (which you never measured evidently) was above 425 psi- and triggered the high pressure cut-out of compressor-- good thing that worked or you could blow a hose with that kind of pressure--a/c needs air flow across condenser to work-- either by driving or by cooling fans that work-

Theoretically the fans should run, but the temp. has exceeded 227 (boiling/bubbling coolant in overflow tank) and the fans don't turn on. If I hard wire the fan plug, they do work. My bad luck for having two independent fan control problems at the same time.

I'm glad the high pressure cut out worked. I don't have a full set of A/C tools or A/C background, thus I made the logical decision of going to an A/C shop after a DIY recharge gauge and refrigerant kit left me with no solution. The recharge kit did work nicely on my reliable, purchased new, '95 Mazda Protege with 235K miles and original engine/clutch, so no loss.

I'm not a trained mechanic, just a moderately skilled DIY car person. Moderate skills include replacing struts, exhaust manifold, tie rods, ball joints, half axles, exhaust parts, control arms, brakes, seat rails, fans, and fixing or replacing stuff on this van.

For my issue...

The fans start with the A/C.

Yet they don't appear to be starting at high temp. I've seen 7/8ths on the coolant gauge, and pulled over to let it cool down, and could hear the coolan reservior bubbling.

Bad temp sensor?

I'll do some checking now, and see if I can find the patterns, given the new data. Thanks!

The coolant temp sensor (top of engine left side) acts as a variable resistor...high value when cold (several thousands ohms) and low value when hot (100 ohms)....

http://www.avigex.ca/xport/thermistor.jpg

www.avigex.ca/xport/enginewiring2of3_19932.pdf


so you can uplug sensor, and try inserting a low value resistance ...100 to 120 0hms into the connector....and see what happens.

...you can also run the engine hot, stop it then measure the sensor resistance with a multitester (ohmmeter): it should read close to 100 ohms.