Auxiliary Fan - Diagnostics/Manual Modification

[ctsoth]

84 300 D Turbo

Does anyone know if there is a troubleshooting guide to discover why your auxiliary fan doesn't work? Can someone provide steps to discover the cause of this unfortunate circumstance please?

Also, if I am unable to troubleshoot it do to specialized tools I would like to put a manual control in, a switch in the cabin. Is there a way to do the modification that makes the switch and wiring look very natural and built in/original?

I pay attention to my gauges while driving, and I am planning boost & pyro gauges so barring supernaturally oblivious behavior I think I could manage a switch.

Thank you for your time!

-Chris

[Jeremy5848]

The troubleshooting guide consists of bits and pieces of the posts in the forum. The DIY section should be searched first, then this diesel section, then the "Tech Help" gasser section because the gassers have the same aux fan. Search for "aux fan" or "auxiliary fan" and your model year. AFAIK, the aux fan in your model is turned on only by a pressure switch in the refrigerant line from the compressor. If you are low on refrigerant, the pressure (or is it temperature?) will never get high enough to trigger the switch. There's probably also a relay and a fuse to check. The various threads that your search will turn up should describe all of these, where they are, etc.

[jkoebel]

If I can find some way to scan things, I can help. The aux fan is part of the A/C system, and I have a copy of the W123 Air Conditioning FSM.

Please use the forum to send me an e-mail tomorrow so I remember.

[Deni]

I don't know if it's the same on the w123, but on my w201 I can check if the aux fan is working properly or not by shorting out the wires of the pressure valve that is on the dryer.

If you short the wires and the fan works than you're most probably low on refrigerant.

[Cervan]

ill post some pictures up tommarow while im fixxing my engines hemorrhage of oil.

[Cr from Texas]

Should be pretty simple to check with a multi meter. With engine running and AC on, do you have 12V at the switch (no - bad switch, low refrigerant, etc.). If you have 12V at the switch, check the fan. If you have 12V at the fan and it's not running, replace the fan.

[ctsoth]

Thank you all for your suggestions and input. I will be checking refrigerant and fan power first . My brother is a pipe fitter so I'll get him to help me with the ac, I have only rudimentary knowledge of ac units. Hes certified to build them ^^

At this time I am going to wager that low refrigerant is the culprit.

[argus445]

on w123 i converted to r134 would this change when this aux fan kicks in? i had a bad relay changed it and nothing i can jumper the relay junction and it works but when is it suppose to be running anyways only like in traffic when the pressure goes really high correct?

[ctsoth]

R134a will not alter the function of the fan, My system has been running converted for 3 years, sat over winter and now its not so happy.

[tangofox007]

Originally Posted by ctsoth

R134a will not alter the function of the fan,

In my experience, the fan will come on later and run longer when R-134a is used.

[mccauleybil]

Since it is finally air conditioning time in Buffalo, its time to learn how the system works on my 1982 300 SD.

Currently, when the AC is engaged, it blows cool (compressor comes on and cool air comes from vents) for awhile, then the cool gives away to heat sent straight from Hades.

On investigation, I have discovered that my aux fan is not running (tight until i manually forced a revolution, and now spins freely). I have power at the relay next to the drivers headlamp connection, but no fan activity.

Any ideas? I am prepared to simply recharge the system and replace the aux fan, but ..... if there is more at issue, I would like to resolve those issues first!

Come on up, the sailings fine on Lake Erie and Ontario

[carnut]

Going from somewhat cool to hi heat could be a torn diaphram in the MONO valve. Or no voltage at the MONO valve to activate it. This valve opens and shuts off coolant to the heater core depending on the temp you've set on the dash temp wheel.

[ngarover]

On my 85 CD I noticed the fan was not working. I jumped the pressure lines and it ran fine, I may be a little low on freeon so I left it jumped till I can get it over to the shop and hook up the gauges and test.

Jumpered, the fan runs all the time but I have noticed that the car can now sit idling on a 90+ hi humidity day and the temp gauge is steady at just a little over 80. Which in North GA is a good thing as I can leave the car and A/C running for 10-15 minutes and not come back to a fricken oven when I goto leave.

[Diesel911]

If you only want to test the Fan itself Follow the Cord down and under and you will find a Connector (The connector/plugs may need to be cleaned).

Simply hook up some wires from the Battery to the Fan and see if it works.

If it does not turn at All I would take a look inside because when I changed the Bearings on my Fan I found all kinds of Dirt and Dead Bugs. Any of that stuff could keep a Motor Brush from making contact.
Remember the Nut that holds the Fan on is Left Hand Threaded. There is a Few DIYs on how to fix the Fan.

[mccauleybil]

I neglected to mention that I have replaced both the thermostat and monovalve in the past week. I replaced the theromstat because it was cheap, and I was unsure of the vintage. I replace the monovalve because the heat seemed uncontrollable.