300SD general issues... - PeachParts Mercedes-Benz Forum

Lain · #1 08-04-2010, 01:39 AM

(from a different forum, each paragraph was a different edit)

I recently bought a 1985 300SD that was used as a commuter car for most of it's life. When I got it, the A/C wouldn't blow any air which I quickly traced to the blower motor being burnt out. Once I got that running I still had the issue of the A\C not blowing cold air. I'm not sure if the relay is switching the compressor on because I'm semi-fresh with cars, but I do know a bit. I managed to jury-rig a switch to kick the compressor on which I used to retrofit the system to R134a, but it still doesn't blow cold air. What am I doing wrong?

I used a simple retrofit kit because after searching the forums a bit, I learned that all I needed to do was evacuate the system then refill it. I had a hard time finding the low end valve, and almost ended up refilling it through the high end valve, but finally found the low end next to the motor block.

Edit: Oops, turns out I have a broken car alarm that doesn't trigger the horn. O.o

layback40 · #2 08-04-2010, 09:19 AM

Welcome to the forum!!
I hope you find out all you need to know.
Guys like Larry Bible on here know that much about aircon on these cars that they should be able to help.
It would be good if you could put a bit of info in your signature so that people know a bit about your car.
There are many threads about aircon, you may wish to have a read of them.

Good Luck !!

thayer · #3 08-04-2010, 09:28 AM

With AC work you are dealing with a pressurized system with very few ways to verify the contents of the system. In order to get the fastest and best answer it is neccesary to explain in detail EXACTLY what you did as these steps give the context clues as to how much of what is in your system.

oh yeah, and you need AC pressure gauges to troubleshoot.

Here are a few tips if you think you have the right contents in the system.

Pinch off the monovalve hose that goes into the car. That will prevent hot coolant from killing your cooling power.

Find the relay that says "KLIMA" and jump pins 5 and 7. That will bypass that relay.

drop your blower and stick a hose gently into the evaporator to pull out all the junk (leaves, acorns, mice/squirril skeletons)

4thesporty · #4 08-04-2010, 11:24 AM

Quote:

Originally Posted by thayer

drop your blower and stick a hose gently into the evaporator to pull out all the junk (leaves, acorns, mice/squirril skeletons)

Did you get alot of gunk out when you did this, if you did this?

thayer · #5 08-04-2010, 11:50 AM

I got most of the list I gave save the bones. I got about 2 measured cups of leaves and acorns out of the evap using a 1hp shop vac (that vac is about the size of a basketball, not a ton of power needed for this)

I didn't even move the hose around that much. It just sucked right out. I bet there is more in there.

4thesporty · #6 08-04-2010, 12:25 PM

Quote:

Originally Posted by thayer

I got most of the list I gave save the bones. I got about 2 measured cups of leaves and acorns out of the evap using a 1hp shop vac (that vac is about the size of a basketball, not a ton of power needed for this)

I didn't even move the hose around that much. It just sucked right out. I bet there is more in there.

Thanks, I have been doing some reading on the subject after you brought it up. I will probably do the same soon.

Lain · #7 08-05-2010, 05:08 PM

Haha, I posted this thread when I was in a slight panic, I didn't know that my car had an alarm (it's broken so the horn doesn't go off) and that ended up killing my battery. When I get a better method of typing I'll change my sig, I'm on my Blackberry. I tried bypassing the relay and the monovalve per the service manuals to no avail, but yesterday I tried refilling the A/C system, and noticed it was empty (!). A while later I heard a hissing noise from the engine bay, leaned down and it smelled like ester oil. I suppose I've got a leak?

dagObx · #8 08-06-2010, 01:45 PM

Lain,
I suggest you wait & get some input from Larry Bible on your AC. He has been dealing with AC issues for decades & will have some good info for you.

My recommendation, if you do not live in Canada, is to retrofit your system back to R-12. It's not that expensive to buy & you will be pleasantly surprised at how the system works for you. I did this to my '87 124 & I'm really glad I did.

Be sure to buy a set of AC gauges for R-12. They can be found on Craigslist or Ebay for not a lot of $$$. You will need gauges whether or not you go back to R-12 or stay with R-134a. They use different gauges, though - R-12 gauges will not work for R-134a. The gauges will allow you to see if your compressor is operating properly & you will have some info to post here so the AC gurus can help you out.

Yes, it sounds like you have a leak under the hood. Might try to put a dye charge into your system if you can't readily find the leak.

warmblood58 · #9 08-06-2010, 02:30 PM

Quote:

Originally Posted by thayer

I got most of the list I gave save the bones. I got about 2 measured cups of leaves and acorns out of the evap using a 1hp shop vac (that vac is about the size of a basketball, not a ton of power needed for this)

I didn't even move the hose around that much. It just sucked right out. I bet there is more in there.

How did you access this on the SD?

Lain · #10 08-06-2010, 05:17 PM

Are you talking about the cavity behind the glove box?

Edit: Aww, vBulletin doesn't update the signature on all posts. I have a 1985 300SD with now 516k miles on it, I think I'm being too specific in my sig though.

thayer · #11 08-06-2010, 05:26 PM

Easy

Pull kick panel from passenger front seat. Helps to also pull the glove box liner, but not neccesary.

Lay down with your head under the dash and feet up around the passenger headrest.

unscrew the bottom of the blower motor case.

Unscrew and unplug the blower motor.

Slide motor out and set aside.

Run hand into where the blower blows, you will notice the fins of the evaporator.....very sharp and fragile....do not bend.

Pull hand out and run shop vac hose into the evap area being sensitive to the fragile fins.

Make sure you start with an empty vac so you know what you got out and can show it off to the forum. Some people have even sprayed water in there to wash it. Not neccesary but could potentially get you another degree of cooling. be sure drain is free if you try and do this, it could cause flooding in the car if you don't.

Reassemble, don't forget which screws go where. Now stand up straight and let the blood rush back in to your body and out of your head....Easy...don't pass out.

Kent

Lain · #12 08-06-2010, 05:32 PM

Aww, I have to take the blower motor out again? When I got the car nothing blew out of the vents, I determined the issue to be a fried blower motor. Had to run to Pick 'n' Pull and yank a motor out of an '84 300SD (great find, matched perfectly save one small screw on the bottom of the motor itself). That got at least my heater blowing. I know what you mean by the headrush after doing weird arches to dig around in the blower motor cavity, still don't know if I got everything screwed back in under there. Just as an extra question, behind a plastic panel under the floor mat there was a module with the Becker brand on it... know what it does? I had it unplugged and the stereo worked without it while I was working on the car.

thayer · #13 08-06-2010, 06:14 PM

I have no idea what ANY of the modules over there do. I just don't touch them unless I have to. The one time I took out the "temperaregulaterminatorvblahglasdgjhaekger" I fried my PBU and had to resolder. It ain't broke don't fix it.

Lain · #14 08-06-2010, 06:16 PM

Works for me.