tired of my fans not working - PeachParts Mercedes-Benz Forum

roundout · #1 07-22-2009, 09:55 AM

I live in Texas and it's hot down here. My car (84 123) has what appears to be a brand spanking new fan assembly in it but it's never once come on. After doing some research here, I've decided that trying to fix it to run as designed would be a waste of time. My A/C quits blowing cold air sitting at a stop light on a hot day, but works when it's getting fresh air over the condenser.

After somebody's loss due to a aux water pump freezing up, I unplugged my aux water pump, to no ill effects.

Does anybody see any reason NOT to rewire the fan to the aux water pump connection and have it run all the time? When it gets cold in the winter I could simply unplug the fan.

Oldwolf · #2 07-22-2009, 10:01 AM

I would say to first debug the current set up to see why it does not work as designed. Might just be a relay or temperature switch that is faulty.

SD Blue · #3 07-22-2009, 10:51 AM

Is your a/c charged with R12 or R134 refrigerant?

I agree with debugging the system as "cross-wiring" things in the auto climate control system could introduce other unknown problems with the pushbutton controller.

BTW, the "fix" for problems with the aux. water pump is an in-line fuse to prevent it from drawing too much current directly from the pushbutton controller.

Jeremy5848 · #4 07-22-2009, 10:53 AM

The aux fan has either a temperature switch in the water jacket or a pressure switch in the refrigerant line or both (I don't remember which your car has). If the fan is not coming on at all, you first need to make sure that any fuses in the electrical circuit are good. Don't just look at them, actually take them out, hold them in your hand, make sure they don't have an invisible hair-line crack.

Next, jump the fan wires directly to the battery to see if the fan will work. Next, check the switches, which ever ones you have, to see if they work. The pressure switch in the a/c line is a common failure point; unfortunately, replacing it requires the a/c system be drained and recharged. The temperature switch in the water jacket is less likely to fail and is easier to replace. I don't know if the '84 300D got both of those switches. Perhaps someone more experienced can help here.

If all else fails you can wire the aux fan through a switch that you can turn on yourself from your seat. Since the fan is rather noisy, I would think you would not want it running all the time. BTW, the aux water pump circuit is probably not heavy enough to handle the current of the aux fan.

Jeremy

RAYMOND485 · #5 07-22-2009, 01:00 PM

1984 300D TURBO 147K
CHECK THE R12 OR R134 MAY BE LOW, AT LOW ENGINE SPEED NOT PUMPING
GAS, LOOK AT THE SITE GAS ON TOP OF THE REC DRYER, SWITCH THE TWO
RELAYS ON DRIVERS LEFT ENGINE FENDER UNDER THE 4 IN SQ BLACK COVER
5 PINS EA

panZZer · #6 07-22-2009, 01:46 PM

Quote:

Originally Posted by roundout

I live in Texas and it's hot down here. My car (84 123) has what appears to be a brand spanking new fan assembly in it but it's never once come on. After doing some research here, I've decided that trying to fix it to run as designed would be a waste of time. My A/C quits blowing cold air sitting at a stop light on a hot day, but works when it's getting fresh air over the condenser.

After somebody's loss due to a aux water pump freezing up, I unplugged my aux water pump, to no ill effects.

Does anybody see any reason NOT to rewire the fan to the aux water pump connection and have it run all the time? When it gets cold in the winter I could simply unplug the fan.

What-Where is the aux water pump on the cars??

roundout · #7 07-22-2009, 02:12 PM

To answer a few questions:

134a. It was converted before I bought it. It had no charge and I had it charged up. It's worked since March and I can't find a leak. I was beginning to believe that it was charged improperly because we had a long stretch of 100+ degree days where the air was just not cutting it. Now that the temp is back in the normal (low-mid 90s) I have no real complaints, other than that it starts blowing warm air at a light. It works fine. It is not low on refrigerant and the compressor stays on the whole time.

I have already swapped the relays on the drivers side fender. The one in front controls the compressor. I haven't figured out what the rear one does yet but it has a known good relay in it.

The fans work when given 12v.

charmalu · #8 07-22-2009, 03:24 PM

Iam not a AC expert by any means, but I do know there has to be air moving across the condensor for it to cool down the freon.

I see no reason the AC fan couldn`t be on all the time in slow traffic.

Charlie

ah-kay · #9 07-22-2009, 03:39 PM

Check out this excellent link on the Aux fan

is the low speed auxillary fan always supposed to come on with ac

panZZer · #10 07-22-2009, 08:30 PM

Can someone tell me about the aux waterpump?

charmalu · #11 07-22-2009, 10:28 PM

The aux water pump is usually on the right inner fender. there is a coolant hose on the R/F just below the by pass hose connected to a nipple on the housing. hose has a "J" on the end that connects to the pump.

hose is right above the Alternator.

Charlie

whunter · #12 07-23-2009, 12:57 PM

Quote:

Originally Posted by roundout

I live in Texas and it's hot down here. My car (84 123) has what appears to be a brand spanking new fan assembly in it but it's never once come on. After doing some research here, I've decided that trying to fix it to run as designed would be a waste of time. My A/C quits blowing cold air sitting at a stop light on a hot day, but works when it's getting fresh air over the condenser.

After somebody's loss due to a aux water pump freezing up, I unplugged my aux water pump, to no ill effects.

Does anybody see any reason NOT to rewire the fan to the aux water pump connection and have it run all the time? When it gets cold in the winter I could simply unplug the fan.

The circuit is too light/weak.
The aux cooling fan should draw roughly 30 AMP at maximum load.

If diagnosis fails, you can cheat:
** Jumper the aux fan connector direct to battery, determine fan terminal polarity that blows air through the radiator.

* Attach a fuse holder to the + battery terminal.
* Run RED wire from fuse holder to the A/C temperature switch.
* Attach RED wire to the A/C temperature switch.
* Run RED wire from the A/C temperature switch to the aux fan connector.
* Attach Red wire to the aux fan connector.
* Run BLACK wire from the aux fan connector, and attach it to a solid ground.
* Install a 30 AMP fuse in the holder at battery.

* Verify that wires will not be pinched or cut by closing the hood.

The fan should turn on any time the A/C condenser becomes hot enough to need it.

Drive cool and be happy.

Have a great day.

roundout · #13 07-24-2009, 10:13 AM

Quote:

Originally Posted by whunter

The circuit is too light/weak.
The aux cooling fan should draw roughly 30 AMP at maximum load.

If diagnosis fails, you can cheat:
** Jumper the aux fan connector direct to battery, determine fan terminal polarity that blows air through the radiator.

* Attach a fuse holder to the + battery terminal.
* Run RED wire from fuse holder to the A/C temperature switch.
* Attach RED wire to the A/C temperature switch.
* Run RED wire from the A/C temperature switch to the aux fan connector.
* Attach Red wire to the aux fan connector.
* Run BLACK wire from the aux fan connector, and attach it to a solid ground.
* Install a 30 AMP fuse in the holder at battery.

* Verify that wires will not be pinched or cut by closing the hood.

The fan should turn on any time the A/C condenser becomes hot enough to need it.

Drive cool and be happy.

Have a great day.

I might do this. Upon further investigation, I think my Pressure Switch is shot. I jumped the two leads on it together and the fan didn't turn on. It would be cheaper and easier to simply rewire the fan control as you've indicated here (assuming my Temp switch is functional). I am unemployed at the current moment, so I need to start factoring budget into all my projects. In the past, that hasn't been much of an issue.