Aux Fans

[DAVID LEE]

This is my first inquiry on the site. I have been reading about aux fans for several days, and using the knowledge gleaned to troubleshoot by A/C problem. I think I'm close to knowing what the problem is, but I would like just a little more info before proceeding with some possible fixes.

I have a 92 300E. My aux fan would not come on when the compressor was running. After reading the archives for several hours, and seeing bubbles in my sight glass, I decided that the first thing I needed to do was to get my A/C charged. That was done today. There are still a few bubbles in the sight glass, but not nearly as many as before, and it seems to cool OK, but it was only in the 80's today.

The aux fan still does not come on at low speed. I jumpered the switch on the redeiver/dryer and the fans came on. I took out the resistor and checked it for continuity, and it checks OK. The fans come on at high speed when temp reaches 100 degress. Is it possible my high side pressure sensor is bad? If so, can the switch be replaced without losing the r-12? My sensor is not on top of the dryer, but comes out the side of the dryer very near the top.

Without pressure gauges is it possible to test the sensor? I have read in one thread about someone wiring a relay so that the fans come on at low speed when the compressor is running. Where would I get such a relay?

Thanks in advance for any help. This site is a gold mine of info.

[Gilly]

It sounds like everything may be normal. You don't state if the AC blows cold air or not, this is the determine factor I guess you could say. The switch you jumped that made the fans come on low speed is the high pressure switch. One of it's jobs is to turn on the low speed fan if the pressure is high enough. The fact the low speed fan may or may not indicate a problem, one possibility is a bad switch (high pressure switch) or the pressure simply may not be getting high enough to activate the fan. The low speed fan does not automatically come on just because the AC is operating. The determining factor on if further diagnosis is needed is if the AC is cold enough for you or not.
Gilly

[Arthur Dalton]

As GB states, the aux fan is triggered with the high side pressure switch.
But they have designed the cut-in point of that switch to
be high enough to be tripped only when the a/c is starting to be burdened/taxed with a high thermal load.
It is quite possible to have good a/c operation in mild ambient temps where the high side pressure does not get to this pressure and therefore does not call/need the assistance of the aux fan to bring down the high pressure , [ which is what drawing additional air across the condensor accomplishes].
The true test is comparing the switch/pressure with gauges,
but usually you will see an aux fan cut-in on a hot/humid day in traffic or at idle when there is low airflow on the condensor..
So watch for fan under extreme conditions..
As far as the resistor and circuitry are concerned, you have already verified that as OK with the jumper test. The only thing not confirmed in that circuit , of course, is the sw cut-in spec. and the sw itself....
The same goes for the high speed fan... once again, a safety devise that only gets called for under extreme conditions..
triggered by the engine coolant temp sensor [ 105C on your car]


Thats the basics....

[DAVID LEE]

Thanks for the replies.

Still a couple of questions. Is it normal for there to still be a few bubbles in the sight glass? The air seems to be cold coming out the vent, but again, the temp was only in the 80's (very rare for charlotte in july but welcome). I took the car to get the A/C charged to a shop that I have never used before. I'm just trying to determine if they did a good job of charging the A/C. By the way, is there a way I could buy some r-12 from someone so that I don't have to pay 60$ a can to get my a/c charged? I read in one thread prices in the 15 range. I realize I can't by it direct from a dealer, but maybe some of the guys on the forum would sell it.

And, if the switch is bad can it be replaced without losing coolant?

What really seems odd to me is that someone would design a car where the high speed fans come on when the gauge temp reaches 100C (while the car is sitting still in my garage), but the low speed fans won't come on when the A/C is running so that the temp won't get to the point where the high speed fans need to come on in the first place. Maybe I'm the only one that finds that design very strange.

I've always had japanese cars in the past and the engine temps seem to stay steady at one temp. It just bugs me to see the guage go up to 107 when it seems to me it doesn't need to. Oh well.

Thanks

[DAVID LEE]

Thanks for the replies.

Still a couple of questions. Is it normal for there to still be a few bubbles in the sight glass? The air seems to be cold coming out the vent, but again, the temp was only in the 80's (very rare for charlotte in july but welcome). I took the car to get the A/C charged to a shop that I have never used before. I'm just trying to determine if they did a good job of charging the A/C. By the way, is there a way I could buy some r-12 from someone so that I don't have to pay 60$ a can to get my a/c charged? I read in one thread prices in the 15 range. I realize I can't by it direct from a dealer, but maybe some of the guys on the forum would sell it.

And, if the switch is bad can it be replaced without losing coolant?

What really seems odd to me is that someone would design a car where the high speed fans come on when the gauge temp reaches 100C (while the car is sitting still in my garage), but the low speed fans won't come on when the A/C is running so that the temp won't get to the point where the high speed fans need to come on in the first place. Maybe I'm the only one that finds that design very strange.

I've always had japanese cars in the past and the engine temps seem to stay steady at one temp. It just bugs me to see the guage go up to 107 when it seems to me it doesn't need to. Oh well.

Thanks

[Arthur Dalton]

<<>

NO- it can not...

< but the low speed fans won't come on when the A/C is running so that the temp won't get to the point where the high speed fans need to come on in the first place. Maybe I'm the only one that finds that design very strange.
Your car is not running as designed and the design is actually quite good..I personally think you are slightly low on freon...
[ or faulty sw] Once again---gauges...
I also would check your thermostat. Is your car running above 100 w/o the a/c on??

I've always had japanese cars in the past and the engine temps seem to stay steady at one temp. It just bugs me to see the guage go up to 107 when it seems to me it doesn't need to. Oh well.
Again, ck thermostat before anything
You may want to do a search on the Japanese temp indicators..

>>

[DAVID LEE]

Thanks for the response.

I just changed the thermostat last weekend so as to eliminate that possibility.

It sounds like I may need to take the car back to the shop to make sure they completely filled the system with freon. That will have to wait till Monday.

Thanks

[DAVID LEE]

Forgot to answer your question on whether car runs hot without A/C on.

No it does not. It stays right at 90C with no A/C on... Hence my obvious befuddlement at the wide temp fluctuations.

thanks

[stevebfl]

You might be thankful for the sensitivity of MB gauges.

I suppose I got to tell a story. The story hinges on the sensitivity of gauges.

I have been driving automobiles for fourty years. I am a repair technician probably because early in life I excelled at making things work and that included many cars of my own and family and friends. I can mostly say that I have never been stuck on the side of the road. I could write reams of the individual instances where i got the car/truck/bike home.

That all came crashing down two weeks ago. My 50k 97 BMW 540 finally got me and gauge sensitivity was most of the problem. A little info on the system first. In the continueing interest of emissions and performance the BMW engine management system uses an electronic thermostat that changes engine temp by about 20-30 degrees. Mostly the car runs hot with no power to the thermostat, but at idle the t-stat is powered and opened and the same occurs under heavy load.

Because this ranging of temp would be very noticable the gauge like many gauges is stabilized, retarded, or otherwise delayed in the actual indication.

So I am headed North on I-75 after standing in the sun all day trying to see the "Tall Ships" in St. Petersburg harbor. About in the middle of Tampa in a driving rain my display flashes the low coolant warning. Well I know all about this and know that the sensor in the coolant tank has been exposed and that level is nothing to worry about. There of course could be a serious leak but I still got the gauge, right? Well 50 miles further down the road its gourgeous out and I'm leading the pack when I get the instantaneous warning "ENGINE IS OVERHEATING" on the display. Knowing I have pushed my luck I dive for the shoulder and the temp gauge is buried in the red (I had been watching this). Within 10 seconds the key is off and I'm still doing 50 on the shoulder while braking hard and watching traffic.

Once totally off the road, in the grass, and stopped, I again switch on the ignition and the find that the gauge is just slightly over the midpoint where it always runs. I get out to view the damage. I am in high grass so i can't judge the size of the leak. The steaming under the hood appears to be the overflow not the leak as the pressure can be felt in the hoses. It is not very hot in reality and in about ten minutes I have the cap off with no boil over only steam. Thank God for rain as a few hundred yards further there is a large puddle in the swail. So I drive the distance and take off my shoes (I'm in shorts anyway) and use the two spring water bottles we have to gather pond water which I then strain through my sock into the radiator.

All filled up I start the car and quickly view the situation and boogie down the road at reduced speed and with A/C off. Again I have the temp gauge right in the center for all 15 miles to the next exit, which I take, learning from my previous arrogance.

I pull into the gas station/mini market, pop the hood and as i am walking to the front I pass over a three inch wide stream of coolant (still pretty green) running just in front of the drivers side front tire. I don't even open the hood. I call my buddie (who owns a wrecker - we are only 40 miles from home).

The point here is complicated. Fifteen years ago I had virtually the same thing happen on the way back from Orlando airport in a 450SEL. I pulled into a mini- market with a quarter inch stream visible from water pump vent hole. I purchased two gallons of milk and emptied it into the toilet. Filled the jugs and the radiator with water and started off. I left the rad cap loose to prevent pressure and decided to go till the gauge moved or 15 miles whichever came first. The milage came first and I filled the radiator from my bottle using about 2/3 of a gallon. I then headed back to Gainesville on 441 rather than the turnpike allowing me to stop about every twenty miles. The leak actually got smaller as I proceeded. I got home in about double the normal two hour drive.

In the recent situation I couldn't do the same for two reasons. The first is that with the t-stat control that is used the system will boil water unless pressurized (normal, unseen, activity brings the temp at times to near 220 I think), I couldn't run without a cap and the second reason is the gauge is closer to an "idiot light" than a usefull idicator of coolant temp.

Personally, I prefer gauge sensitivity!

[DAVID LEE]

What a story!!!!

I've just been driving the car one month and am trying to fix 10 years of neglect. It's funny all the "little" things you discover once you finally get a car home and start driving it.

For instance... I just noticed that one of my aux fans does not always start. If I spin it with my hand, that gets it going. I suppose that driving down the road, it would probably eventually get going, but if stuck in traffic, it probably would just sit there useless. After taking about an hour and a half to try and figure out how to get the thing out I gave up.

Is this an all day job just to get an aux fan out, and can the bearings be lubricated, or is it just a throw away?

Dave

[Gilly]

"Strained it through my sock". You're a classic!
Gilly

[Cap'n Carageous]

I like the one about buying two gallons of milk and pouring it down the toilet just to get the jugs!!

[DAVID LEE]

Still trying to figure out how to get aux fan out of 92 300E. It is the passenger side. Remove headlights, bumber, or something simple?

Can't figure it out without just taking things apart piece by piece.

Thanks,

Dave

[Gilly]

You have to take out the whole assembly, then seperate the 2 fans.
Removing both headlights sounds right, bumper can stay attached. Take out the push in fasteners that hold on the protective cover and then I think it'll make sense.
Gilly

[DAVID LEE]

Thanks for the reply. It is much appreciated.

I was afraid the answer would be "take out the headlights". Maybe that won't be too hard. We'll see.

Dave