auxillary fan switch
 

84 300SD. All aspects of A/C work perfectly (vacuum actuators, expansion valve, evaporator, compressor, etc.) but my darn high temp. switch to auxiliary fan is out. I don't want to have my R-12 removed and replaced (probably close to a full charge) just to pop in a new switch (new drier at same time of course). I know some of you have just wired it for manual switching at creeping traffic conditions, but I'm sure to forget to turn it off. Is there any thing else dependent on this switch or just aux. fan; and since all front wheel drive cars(dreaded non-Mercedes) use electric fans that don't fry, will it hurt to just hard wire it ON all the time and let the thermostat take care of the increased cooling capacity thus obtained? I like my engine temp. to NEVER be above minimum spec. if possible(obsessive/compulsive about that). Sorry about verbosity. Thanks.

[Edited by jbaj007 on 07-22-2001 at 09:11 PM]

You've got 2 choices fix it or don't fix it. That's all I know to tell you.

On your receiever/dryer are mounted two switches:

1. Refrigerant temperature switch: Activates the aux. fan when this switch detects a temperature above a present point (~62C if I recall correctly). This switch is mounted at the top of the receiver/dryer. Shorting the leads to this switch will force the aux. fan to be always on. You do not have to evacuate the refrigerant to replace this switch.

2. Refigerant pressure switch: Disables the AC compressor if there is insufficient refrigerant. This switch is mounted in the side of the receiver/dryer. Shorting the leads to this switch will cause the compressor to engage regardless of the amount of refrigerant in the system. You must evacuate the system when replacing this switch.

How do I know all this? I have the exact same car and my temp switch was broken so I jumped the leads so the fan would stay on. My pressure switch then gave up the ghost and vented all my new freon. I have ordered a new receiver/dryer and both switches and am contemplating a switch to R134A. (I read up on the subject in my W126 Service CDROM).

Chris Blanchard
1984 300SD 140.8k

There are of course two switches on the dryer. One is a low pressure cut-out (which got updated to a low and high pressure cut-out) and the temperature switch. I guess the big question here is: Has the temperature switch been converted to the later type or not? The later type works on pressure rather than temperature and enters the pressurized part of the dryer. We were supplied with the later switches and updated dryers almost ten years ago at the dealer. If your switch is a brass-looking piece it's the old one that doesn't enter the pressurized part of the system. If it has red(or green)plastic on it, it's the later one and requires a discharge/recharge to replace.
Regards,
Randy D.

Aux fan problems
 

My 190E is running warm and the aux fans are acting strange. I have been told it might be the pressure switch for the A/C. I need to know more about the low and high speeds the fans run at and when. Also, I was told that the Fans not turning on sometimes might have to do with the fact that the A/C might need serviced and the pressure in the system is not high enough to kick the fans in...does this seem like a possibilty? The fans run fine when you force tehm by shorting out sensors. SOuld the fans every stay running after the car is turned off to continue to cool like most all american cars do? Also, Should the fans always come on when the A/C is turned on like most american cars do?
Thanks
Christopher

These fans only run when the engine temp is high enough to engage them or when the AC in on and the pressures are high enough to activate them. They are two stage fans and they will speed up as the AC pressures rise. If they are not operating with the AC check the AC pressures and if the pressures are enough to engage the fans and they still don't work check the fan resistor located by the receiver drier. You should also check the high pressure switch located on the receiver drier. It's the one with the pigtails. You can bridge these two wires together and the fan should run if the fuse and resistor are okay.

Randy. I've got the original temp. switch (brass) so I'm "good to go" on the replacement w/o discharging system. Your answer is to the point and covers the problem completely. You're obviously a pro (saddled with us DIYers).
Thanks.

Stan,
Thanks a lot for the info, I was guessing that the pressure in my A/c is not enough to engauge fan. I am intending to have it checked and serviced. It is a 1990 190E 2.6. One of the switches at the drier is partially red plastic. WHich switch is which and which one can I replace without losing all the r-12 and which one can I replace. I guess it might just be best to replace them both when the shop does the service and replace all the r-12 them huh. Thanks. I did replace the fan resistor last month. I want to replace the thermostat this week just to be sure all is good. I can get teh fan to go to the hi speed be jumping it so I know it works at that speed, the system just usually doesn't engague the hi speed.

Hi Christopher,
On a 190e you don't have a switch that isn't in the pressure circuit. Either one you remove will dump your R-12.
Regards,
Randy D.

Randy,
Thanks a lot for saving me! Good to know both switches/sensors dump the r-12! Hey, Question.
SHould a guy replace the drier when he is replacing the switches? Seemed like that was the trend from the notes people have left here. Also, I am very handy, but not too knowledgable on the A/C. What can I look for to indicate my R-12 pressure is low...I think it is. WHat should I see in the sight glass? Bubbles good or bad? Also, I was thinking how easy it would be for me to just order the new switches on the drier and the drier and install them myself, let the r-12 dump and then take it to my normal shop to have it recharged with r-12 and checked out for leaks. What would be bad about me doing this? Is ther anything special I need to know to do this? It sure would save a lot of cash by doing the replacement work myself. And parts are so much cheaper online that at his shop.

Hi,
Well, from an ecological/sunburned penguin/"we're all gunna die"/God loves trees point of view...please don't release fluorocarbons into the atmosphere. Any registered shop will have recycling equipment to safely suck the freon from your car (until their tanks get full and they have to dump it) :).
All Eco-terrorist kidding aside,though not absolutely necessary, yes it is a good idea to replace the dryer when working on the system.It isn't an absolutely necessary thing, but if you replace the switches the system will be exposed to "air" longer than if they did it. It's a personal choice sort of thing. I do my own A/C work(under license by he state of Wisconsin)and I know how long I've vacuumed a system, if it has been open etc... so I don't really feel the need to replace every single dryer if the system hasn't been exposed to moisture(air) for very long.
Regards,
Randy D.

Rnady D,
I feel your pain...tell you what...I won't vent fluorocarbons into the air if you answer one more of my posts... :D
two questions...
question one - should my aux elect fans come on..at least at low speed when ever I turn on the A/C?

and question two - what is the systems max capacity of R-12 and since it is so expensive and it will dump when the drier and switches are replaced what is wrong with converting it to R134a?

No venting here man.

Thanks for all your help. I understand the basics of A/C only. Engines yes, suspension yes, electical yes, A/C NO!:)

Christopher

R-12 Capacity....etc
 

Hi Christopher,
The capacity for a 201.02 chassis is 1Kg (2.2lbs) of R-12.
The auxiliary fan won't come on until the system generates enough pressure to close the switch. So simply turning the A/C on will not make the fan work. If that were the case, the fan(s) would run even when going down the expressway when they weren't needed.
As far as converting to R-134...opinions range from one extreme to the other. Officially, the rubber seals and refrigerant oil for R-12 systems are not compatible with R-134a. So, you are supposed to replace all of the O-rings and the dryer, then remove the compressor...drain the oil, flush the system...etc. A guy around here just changes the fittings and shoots 'em full of R-134a. I'm waiting to hear what happens after a few years. We'll see. The few that I've done have had everything replaced like you're supposed to (usually after a compressor melt-down). The only complaints are slightly lower efficiency at low speeds and "marginal" components leaking under the slightly higher pressures of 134a.
Regards,
Randy D.

Randy D,
Thanks. I appreciate your help. I think I might have the switched and the drier replaced when the A/c service is done and just see what happens. IF the fan is not automatically supposed to come on w/ the A/c like so many american autos that is good. I figure that the fan doesn;t come on or run until the engine cools past triger temp after the car is shut off also. If this is the case, maybe my fan isn't as messed up as I thought. Maybe teh pressure is just low in the A/C.
Christopher