A/C aux fan

[KenB]

Last summer my aux fan blew a fuse 2 times when turning on the AC. Then no problems all summer. This year it didn't blow a fuse but seems slow to turn on. I've read in the archives that it is dependant upon system pressure as well as coolant temp.

Sometimes it comes on as soon as I turn on the AC (while at normal operating temp) other times it takes a few seconds. It will also turn off, the temp creeps upto almost the 3/4 mark on guage and then turns on and drops rapididy back to normal. Also when it turns on while idling it seems like a big load on the motor, you can feel it as seems to shudder a little when it starts. Doesn't sound noisy while operating. I have to get out of the car to go around front to hear it.

A few questions come to mind:

Is the fan supposed to come on immediately when you turn on AC, even when engine is cold? Should it stay on all the time when operating AC? Is the AC not telling it to turn on and it's getting that signal from the coolant temp sensor when the guage is rising towards reading 3/4? Is the fan one or 2 speeds?

Is the aux fan going bad or freon low? System blows very cold at all internal blower speeds, just changed cabin filter.

Will a freon addition/top off cure it if that is the problem? That should be cheaper and easier than replacing the aux fan. My mech says $500 for fan, although BMA has it for $220, I guess the rest would be labor?

Too many ??? Any help would be appreciated.

[mikell]

[QUOTE=KenB]
Is the fan supposed to come on immediately when you turn on AC, even when engine is cold? Should it stay on all the time when operating AC? Is the AC not telling it to turn on and it's getting that signal from the coolant temp sensor when the guage is rising towards reading 3/4? Is the fan one or 2 speeds?

Yes, it's supposed to come on when the A/C is on, regardless of temp. And stay on.

It's 2 speeds.

The Bentley has a test procedure - so, look there to see how to check it out. Could be your problem is the resistor or the relays (2 of them - one for high speed, one for low speed)

Good Luck

[joshua43214]

I am almost positive aux fan on the '93 is pressure operated and should not run constantly with the ac on. On a hot day with the engine warm, it will probably have enough pressure to start the fan right away.

If the fan was blowing fuses, and is slow to spin up, then does not spin fast, the motor is probably bad. If you have some time on your hads, you can try to pull the motor and put a SMALL drop of oil on the rear bushing, this can actualy be a long term fix provided that nothing has galled in there.

The main fan should be able to maintain temp at 1/2 gauge at idle, if the aux fan is inop or slow, it will have trouble keeping the temp down on a hot day w/ AC on. Normaly on a hot day, the fan will run constantly with the AC, and yes it does put a big load on the engine and the car will often shudder as the alternator picks up the load.

Its possible you have 3 problems, bad fan clutch, bad auf fan, and low AC charge and/or a bad expansion valve.

verify that the fan clutch is working properly.

Check the aux fan operation, if you have a shunt and an amp meter, this is the best way, but simply observing its operation may be enough to diagnose it as being slow or sticky. try taping on the back of the motor, if it speeds up, its bad.

If the motor is good and both fans oeprate properly, have a competant AC person make sure the expansion valve is functioning properly and it has the proper charge. Incorrect ac charge coupled with a bad expansion valve can cause low high side pressure allowing the aux fan to shut off.

[KenB]

Thanks to both of you for the info. I just came in from observing it for a bit. I think the problem is not enough pressure in the AC system. I can see at the sight glass that there are a fair amount of bubbles going through.

When the fan does come on it spins up fast and operates normally. While idling it will come on at just over the 1/2 way mark on the dash temp guage and shut off when it drops back down to 1/2. No problems with fuses.

The fan clutch is good, it was just replaced along with the water pump, etc last year. It stays at the 1/2 mark while driving at a steady speed. When in stop and go temp will go up towards 3/4 then right back to 1/2 when the fan turns on. I think it is being activated thermally and not by the pressure in the AC systemas it shuts off when getting back to 1/2.

Will take it to an AC shop ASAP to have it checked and/or recharged. It has never had AC service in the 3 years and 70k that I've had it. It's due.

Thanks again.