w123 a/c drier pressure switch for fan? - PeachParts Mercedes-Benz Forum

BenzTurbo · #1 04-02-2014, 06:16 PM

I'm about a week away from upgrading my a/c on my car. I know there is a temp switch for the fan on top of the drier and a pressure switch near the liquid line from the condenser to turn the compressor off for too high or too low of pressure. I currently have a relay rigged up to turn on the aux fan whenever the compressor is called for. But it is silly to have that 20 amp load when im on the highway... is there a dual use pressure switch or lower temp Switch to kick the aux fan on at a lower temp/ pressure? I don't like the factory setup where it waits until the last minute and my head pressure is like 350psi haha!

Air&Road · #2 04-02-2014, 07:40 PM

The proper temp switch in proper working order along with a properly charged system should handle the aux fan properly. The purpose of the aux fan is not for engine cooling. It's purpose is to prevent excessive high side pressure.

Hope this helps.

BenzTurbo · #3 04-02-2014, 08:23 PM

Quote:

Originally Posted by Air&Road

The proper temp switch in proper working order along with a properly charged system should handle the aux fan properly. The purpose of the aux fan is not for engine cooling. It's purpose is to prevent excessive high side pressure.

Hope this helps.

I know it's only job is to kick the fan on when the head pressure builds like when idling or in traffic but I have noticed it waits way too long to do so. When it's 100 outside and my vent temps climb to 65 degrees, it has waited too long and the head pressure is I'm sure very high. I was going to get one of those adjustable fan controllers and stick the probe on the liquid line out of the condenser but I heard there are lower temp/ pressure switches from later benz's that are good for this. Or adding resistors to the switch to trigger the fan relay sooner.

BillGrissom · #4 04-02-2014, 11:47 PM

Insure the temperature switch is in tight. It is not a pressure boundary, just a tapped hole that it screws into w/ a straight thread. You need it tight to read correctly. Might help to coat the end w/ heat sink compound. A resistor wouldn't work. It is not an analog sensor, just an on/off switch that controls the AC compressor clutch directly. You would have to find a lower temperature one that fits.

Have you measured your refrigerant pressures? If too low or too high refrigerant fill, it won't blow very cold air.

tangofox007 · #5 04-03-2014, 12:01 AM

Quote:

Originally Posted by BillGrissom

A resistor wouldn't work.

It would if used to bias the temp switch. Just like a biased thermostat.

Quote:

Originally Posted by BillGrissom

It is not an analog sensor, just an on/off switch that controls the AC compressor clutch directly.

The compressor clutch is not powered through the temp switch. The temp switch actuates the aux fan relay.

rscurtis · #6 04-03-2014, 10:02 AM

What refrigerant are you using? If it's 134, you're banging your head against a wall.

BenzTurbo · #7 04-03-2014, 11:28 AM

I'm using 134a but by next weekend, I will have my sanden enhanced sd7 and parallel flow condenser bolted up. I have to wait for the mounting bracket to arrive and pull the last 2 hoses that don't come in the kit I'm ordering and drop them off at hosefast to be rebuilt. My a/c works now but as we all know as soon as it creeps over 80, the vent temps begin to rise with the outside temp. I have a large w126 aux fan on it now and when idling, it makes a huge difference when it is on. I was just curious if there was lower pressure or temperature switches that thread into the drier to trigger the fan? There is nothing wrong with my system now. I just wanted my fan triggered sooner.

ROLLGUY · #8 04-04-2014, 11:58 AM

I have had great success with a relay that runs the aux fan whenever the compressor clutch is engaged. That seems to me to be the easiest/cheapest way to go....Rich

crazy4diesel · #9 04-04-2014, 12:29 PM

Quote:

Originally Posted by ROLLGUY

I have had great success with a relay that runs the aux fan whenever the compressor clutch is engaged. That seems to me to be the easiest/cheapest way to go....Rich

Hi Rich,
How did you wire this up? Which relay? Also, when my fan runs the blades are hitting the wire part of the fan housing that faces the condenser, is there an easy fix for this?

I've bought the parallel condenser you mentioned from Ebay, and have the sanden 7 cylinder compressor and a new lower line. I have a new drier, and a new expansion valve (that's the boxy metal thing connected to the evaporator, right?)

What else should I acquire? Especially while I have the dash and heater box out.

Thank you!

BenzTurbo · #10 04-04-2014, 02:31 PM

Quote:

Originally Posted by ROLLGUY

I have had great success with a relay that runs the aux fan whenever the compressor clutch is engaged. That seems to me to be the easiest/cheapest way to go....Rich

Yes, that's what I have now. It's just a little ice cube relay and bracket at the drier to trigger the factory relay. It works great cooling wise but it's not necessary to have the fan running like when on the highway or when it's cold.

ROLLGUY · #11 04-04-2014, 08:07 PM

I am not sure of the terminal numbers, but the coil gets hooked up in parallel with the compressor clutch, and the 2 normally open terminals get hooked up to +12v and the + of the fan. That also removes the aux fan power from the factory fuse circuit (known problem on 126's), and gets it's power directly from the batt. I just used the terminal in the glow plug relay. It is best to put a fuse in-line as well. One could also use the compressor clutch wiring to energize the relay to turn on the fan AND engage the clutch, thereby removing the clutch as well from the problematic circuit.

BenzTurbo · #12 04-08-2014, 03:59 AM

So I found that w124's use the high side pressure to activate the aux fan. They sometimes have two fans, a engine coolant trigger, and even different speeds but I'm just talking about how the a/c calls for extra cooling. There are 2 different pressure switches one being red and the other green. The red has lower pressures since it's designed for r12 but that's what I'm going to use. On another note, is there a larger drier anyone has tried using? Not larger around but taller. Since I'm going to be using a parallel flow condensor, I like the idea of having more liquid storage...