A/C mod to turn Aux Fan on right away?
 

This is regarding my '88 300TE.....I know you diesel guys are more experienced with the A/C systems....

My '87 260E's turns on the aux fans right away when the A/C is turned on to improve performance (must have been dealer mod) and I want to do the same with my 300TE.

Anybody know how to achieve this the easiest way?
Right now my aux fan does not turn on basically at all. I know it works because I've heard it, but the A/C never clicks it on. I think performance would be much, much better if it were running all the time when the A/C is on.

Thanks guys!

Without having the electrical schematic for your vehicle, I would suspect that you could just wire the fan relay in parallel with the compressor relay.

manual switch parallel with low pressure switch
 

You asked simple, so run wires connected to each lead of the low pressure switch on the receiver/dryer to a manual switch in your interior. Flip the switch, and the fans will be on at low speed:D

Sort of related, I ran wires connected to the temperature sensor on the block for high speed fans. The sensor kicks them on when engine temp over 105, but I wanted to run them in the summer for about two minutes before the engine is turned off to keep the temps at 90 or lower. I used a MB overhead light switch installed in the center console as the manual switch.

The post above is a cleverer idea though.

Your refrigerant is low. Get the pressures right, and the fans will come on almost immediately like they did when new.

+1. It is possible that your freon is low and it is not kicking in the high pressure switch at the rec/drier. Alternately, the said switch on top of the rec/drier is faulty.

Jump the switch on top of the r/d and the fan should come on at high speed immediately when you call for A/C. Yours is a 88 and works on pressure. The switch on some old MBZ models works on temperature.

The fans on my W126 come on almost right away. I may re-wire it such that the first speed comes on whenever the compressor is on, and the 2nd speed comes on whenever the refrigerant temp switch closes.

-J

If that is the case, what is the purpose of the temp switch?

http://catalog.peachparts.com/ShopByVehicle.epc?q=1988-Mercedes--Benz-300te-Climate--Control&yearid=1988%40%401988&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6240%3AED%7C10000013%3AMBC %7C1521%40%40300TE&catid=242213%40%40Climate+Control&subcatid=242240@@A%2FC+Temp%2E+Switch&mode=PD

That would explain my findings today with my TE. Guess I need to pull my vac pump out and do the purge and fill dance.

I believe when I checked my pressures were good. I think it was ~80F that day.

http://www.w124-zone.com/downloads/p.../on1-jan11.jpg

The reason that my 260E's turn on right away is whatever mod the dealership did....There is some sort of relay and wiring going on by the R/D...Maybe I'll get the part # of the relay and that may help to figure out what they did. I do remember it being bosch.

Go ahead and post the correct info for the OP. There is no need to challenge me, it is uncalled for. I do not own any gas MBZ. I did say some old MBZ works on temperature, may be 1988 is oooold.

If it woks on temperature then put the sensor in a tub of boiling water and measure the resistance. Jump the wires with a resister of the same value. The principle is the same.

We are not dealing with a rheostat here. It's just a switch; it's either open or closed. No resistor required.

What leads you to believe that those pressures are good?

So typical
 

Another typical example of withholding info. If you knew the answer then why didn't you just posted it in the first place. You feel better if OP and whoever comes back to beg for more info.

ditto

looks like a low charge to me

a 10°F swing in guessing temps is difficult to know what your pressures SHOULD be, but that looks low to me. 134 assuming... your coil temp is at 0°c that's kinda cold... unlikely balanced pressures... I'd expect 200ish high, and 45+ low... get your coil temp up around 35F...