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  #1  
Old 08-01-2008, 08:33 PM
1992 300D 2.5T
 
Join Date: Aug 2008
Location: Atlanta
Posts: 59
!992 300d A/C and electric problems

Good afternoon. I recently purchased a 1992 300d 2.5TD. It has 260.000 miles. I have a few problems with it, so I will start with the A/C. When I bought it it was still on R12 and the air was blowing very little cold air and the compressor was working. I took it to Precision Auto Tune and they retrofitted it with R134a. After the retrofit no cold air was blowing and the compressor will not start. I took it back and the mechanic told me that one of the front fans(driver side) was not working and I need to change them before they can do anything else. After I read the post on this website and got a little acquainted with the AC system I discovered that the fan on the passenger side is for the AC and the one on the driver side is back up for the engine fan/clutch. Am I right ? or both of them are for AC. If I bridge the pigtails on the red temp switch connected near the drier the left fan is working at full speed, but if I leave it connected the fan will not start even in hot weather and at idle ,also if I short the to wires connected to the low pressure switch the compressor starts. My question is, do I really need to replace both fans or can I just replace the pressure switch, drier and red switch with pigtails for now so I can get my AC running.

My second question is about my battery being drained after 2 days of sitting in the garage. If somebody has an idea of places where I could look would be great. I disconnected the amplifier and the radio from the trunk, because I installed an after-market stereo and I checked all the courtesy lights, including the trunk and everything is off. I did notice that after I close it there is a humming sound coming from somewhere behind the driver seat.

So these are my questions, any help or suggestions will be highly appreciated.
Thank you

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  #2  
Old 08-01-2008, 09:39 PM
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Join Date: Oct 2005
Posts: 4,263
I don't know how your fans were designed to work, but one is probably sufficient for R12. Probably not for R134a, but it may work anyway. If it were my car, I would add a relay to energize the second fan.

You do need good airflow for proper AC performance. If your fan clutch is original, you should ensure that it is in working order.

Is the pressure switch currently open? If so, you should ensure that you do have static pressure in the system. It should read 70+ PSI, with the pressure dependent only on the refrigerant temperature. If you have pressure and the switch is open, you need a new switch. If you have no pressure, of course you have a leak.
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  #3  
Old 08-02-2008, 12:15 AM
compress ignite's Avatar
Drone aspiring to Serfdom
 
Join Date: Feb 2004
Location: 32(degrees) North by 81(degrees) West
Posts: 5,554
I Believe

Low Speed Auxiliary fans (They work in concert) are for the A/C Pressure
Switch [you're fooling with crossing it's leads]

High Speed Auxiliary Fans are in response to high engine temperature.

The way they get two speeds out of the fans is to run the current through
a Heavy Duty Pre-Resistor which lowers power to the fans giving you Low Speed.

The High Speed is straight 12 volts at whatever the system will deliver in Amps.

Here's the wiring diagram for the Auxiliary fans.(Below)

It sounds like you may have one fan that's bad...BUT only way to tell is to
separate the wire leads for the two fans (A Journey in itself) and see if it
works with direct 12 volts applied.

Testing for current drains is mostly trial and error with a multi-meter ...
pulling fuses until you find the offending circuit and then the BAD device
on the circuit.

[Unsolicited Comment...Those dudes have done you no favors by converting
your system to R-134...And they F**ked Up the conversion...The A/C should
WORK EVEN WITHOUT THE AUXILIARY FANS FUNCTIONING...on top of it all
They've either insulted you by lying to you about the whole thing(A/C no
workee without fans Workee) OR they are trying to "Blow You off" and get
out of fixing it.] Time to find a Lawyer named "Uncle Vito".
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!992 300d A/C and electric problems-screenhunter_04-aug.-02-00.17.jpg  
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Last edited by compress ignite; 08-02-2008 at 12:31 AM.
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  #4  
Old 08-02-2008, 02:47 AM
1992 300D 2.5T
 
Join Date: Aug 2008
Location: Atlanta
Posts: 59
The fan on the driver side is dead, I can hardly turn it with my hand. As for the guys at the shop I took the car back and their solution was to lower the pressure in the system so the compressor started cycling again. When I got home I saw that they disconnected the temp switch and the low pressure switch. Why, I don't know but in the process they managed to brake one of the connectors on the low pressure switch. Now nothing is working. Before the passenger fan was rotating slowly, now it's dead.

Anybody knows a good AC workshop in the Atlanta area? or is it something that I can fix at home?

I have no problem with getting my hands dirty, but this is the first car that I had problems with the AC and I'm learning.

Some steps or a simple guide to help me change the switches and the dryer , without damaging the AC system will be great.

Thank you
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  #5  
Old 08-02-2008, 01:45 PM
compress ignite's Avatar
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Join Date: Feb 2004
Location: 32(degrees) North by 81(degrees) West
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A/C screwed up even more

O.K. "Search" and "Advanced Search" function buttons on this forum.

There are more competent Independent Mercedes wrench turners in
the Atlanta area than you can shake a checkbook at.Go to the forum
section "Good M B Shops" (Look in Georgia>Atlanta)

Do you have the equipment to evacuate and recharge the system?
(Do you have the knowledge and experience?)

(ANOTHER Unsolicited Comment:Are any of these people related to you?
Have you paid them for screwing up your A/C? [AND you have receipts?]
If this transaction was not a "Freebie",these Hacks are indebted to you
until your A/C is "fixed".Take the car to one of the Atlanta Mercedes
Dealers[RBM,Buckhead,Atlanta Classic,South Atlanta][call first and
speak to the Service Director and explain the situation]AND call the
Hacks and explain that you are going to have your car fixed Professionally
AND then sue them [The Hacks] for the cost in small claims court.)

Your immediate problem is that the Hacks have screwed up your car TWICE
and finding some one to correct their incompetence and complete
the repairs may be slightly more effort than if you'd taken the car to
someone who KNEW WHAT THEY WERE DOING!

I am truly sorry for your troubles(especially in the midst of Atlanta's
Blast Furnace High Summer)

EDIT: RANT commencing
The Precision Auto Tune Hacks are exactly the kind of people who give
everyone else in the automotive repair industry a bad name...AND that's
not right!
You will be doing your fellow consumers (And every conscientious Mechanic)
a big favor by recouping your costs.
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Last edited by compress ignite; 08-02-2008 at 02:34 PM.
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  #6  
Old 08-03-2008, 01:58 AM
compress ignite's Avatar
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Location: 32(degrees) North by 81(degrees) West
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Addendum

In disabling any hope of the Auxiliary fans working(You did say They disconnected most of the terminals and broke one?)They are assuring that your
compressor will overheat/overpressure and fail.
Without the low speed fans, in Atlanta traffic, in this heat the high side pressures in your A/C will climb until something lets go.
Without the High speed fans there is a chance of engine overheat and
"That's the Ball game" as they say for your engine.

It's almost as if they are gonna make sure that you are F**ked.
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  #7  
Old 08-03-2008, 11:07 AM
1992 300D 2.5T
 
Join Date: Aug 2008
Location: Atlanta
Posts: 59
Sadly it was almost a freebie (no receipt) because I knew on of the mechanics and he introduced me to the AC guy who ""fixed"" my car but after my second encounter I had a nice chat with the owner of the shop and he apologized and offered to pay for the repair of the low pressure switch and changing the refrigerant which is something I would not have expected being a non receipt transaction.
In the mean time after I did some research on the forum and I fixed temporarily my AC and I discovered what was draining my battery.

I got the multi-meter and connected it in series between the - battery connector and ground wire ( thank you "compression ignite" ) and before I disconnected the antenna in the trunk I was having 3 amps of consumption, after I disconnected the antenna it dropped to 0,15 amps which I think is right, after reading some other posts. I think the fuse for the antenna was number 6.

As for my AC, I cleaned the pigtails on the AC refrigerant temp switch and I soldered back the broken pin on the low pressure switch and like magic the AC blows nice cold air again and after idling for a while with the AC turned on the passenger side fan started at full speed. Anyway I will have the car in another shop next week to get a new pressure switch and a system check.

Thank you for your help, and as for me this will be the last time I will ever visit a P.. Tune, from now on MercedesShop.com is the way to go..

I do have one question for you guys, do you think it will be ok this summer to run the AC with only one aux fan working (I am a little low on budget, I just moved from Alabama). I drove the car in heavy traffic without AC and the water did not went above 85 celsius and I know the fan clutch is working. Thank you.
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  #8  
Old 08-03-2008, 11:12 AM
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Join Date: Oct 2005
Posts: 4,263
If you have the original pressure switch on the dryer, I would not run it with a single fan. The original switch does not shut the compressor off if the pressure gets too high. Any replacement switch purchased in the last decade should. The water temperature doesn't tell you how hot your AC system is getting, but the pressure switch gives some indication.
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  #9  
Old 08-03-2008, 11:33 AM
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Location: Sonoma Wine Country
Posts: 8,402
Another lesson in why "cheap is not good, good is not cheap."
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Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
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  #10  
Old 08-03-2008, 02:07 PM
1992 300D 2.5T
 
Join Date: Aug 2008
Location: Atlanta
Posts: 59
Well then I guess I am going to park the car for the rest of the summer and use the other one, until I get it completely fixed.

Thank you for everybody's input.
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  #11  
Old 08-03-2008, 03:39 PM
compress ignite's Avatar
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Hooray!

One question:
Are you saying in your reply #7 that you now have one fan(The formerly not
functional) at high speed and one fan at low speed?
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  #12  
Old 08-03-2008, 04:14 PM
1992 300D 2.5T
 
Join Date: Aug 2008
Location: Atlanta
Posts: 59
No I have just the fan on the passenger side working at full speed. The one on the driver side is toasted, I can barely turn it with my hand and applying power to it directly has no effect .I think the bearing or the electric motor is dead.

I found them both on ebay and I going to purchase them later on this autumn.
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  #13  
Old 08-03-2008, 04:37 PM
compress ignite's Avatar
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Location: 32(degrees) North by 81(degrees) West
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Two thoughts

1. if your Auxiliary Fan(s) are running on the High speed it's because the
engine temperature sensor (For the Fan relay) is sensing temps OVER
whatever the Safe Zone is.
2. There is a "Thread", here somewhere,in which the member has a pictorial
on how to R+R the bearings on these fans...
It's for the W123 fan,But the W124 is similar:

http://www.peachparts.com/shopforum/showthread.php?t=98493&highlight=Aux+Fan+Bearing%2FRebuilt+123+Body
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Last edited by compress ignite; 08-03-2008 at 04:48 PM.
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  #14  
Old 08-03-2008, 04:42 PM
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Join Date: Oct 2005
Posts: 4,263
I bought a fan for my W210 from an ebay seller. It lasted about nine months. You may have better luck.
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  #15  
Old 08-03-2008, 05:18 PM
1992 300D 2.5T
 
Join Date: Aug 2008
Location: Atlanta
Posts: 59
So from what you are saying "compress ignite" the one working fan should work only in low speed for the AC and when is on high speed is because the engine temp is to high, not the AC.
That means that the temp sensor for the engine is broken. Because the fan went on full speed with the engine cold (I just stared the car in the morning, and the temp gauge was under 40) and as soon as I turn the AC off the fan keeps working for another minute after which it shuts off. If I turn the AC on again in a minute the fan starts working again.
But anyway I will fix the broken fan and the pressure switch and after that I will continue with the rest of my 300d endeavor.

As for the fans that I found on ebay, they are new and they cost 200 $, but I will try to fix the bearing first.

thank you

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