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  #1  
Old 01-30-2007, 09:06 AM
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heater\AC\blower issues

Hey all, been browsing a while, but this is my first post.

I got a 1981 300sd a while ago, and need to get the AC going because I am in the Phoenix area and its already starting to get hot. Here are my symptoms:

-climate control works

-heater works, but when heat is on, does not blow hot in the rear seats but does in the front seats\defrost area.

-blower is strong in the back seats, very week in the front - also a lot blows out the defrost area

-when ac is on, I can hear the compressor, and the engine's idle goes down a little, so it sounds like that is working, but no cold air anywhere.

Does this sound like it may just need a recharge? And can I get a kit for these cars at an autozone?

And I know there are different issues that cause weak airflow to the main vents, and most of it goes to the winshield defroster area, but not sure what to check first.

Thanks for any info!!!

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  #2  
Old 01-30-2007, 09:34 AM
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Location: Mount Holly, NC
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it sounds like the servo is not cutting off the heat, and you are getting heat with the a/c on. it could also be a dirty evaporator... sorry.
it also sounds like you have vacuum modules that are not shifting the vents correctly...
John
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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  #3  
Old 01-30-2007, 11:25 AM
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Well if I set the temp all the way high, it will blow hot air. If I turn it to "cold" it will turn on the compressor and blow ouside temperature air in. If I turn it to Economy mode, it blows the same exact temperature air in. Would this still indicate that the heat is getting into ac?

Oh and how would I clean out a dirty evaporator?

Thanks!!
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  #4  
Old 01-30-2007, 11:33 AM
vstech's Avatar
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no, that would indicate a bad compressor... or no freon in the system. if the compressor is working as you say, you can feel it engage, then you need to have the freon checked, and at the same time, they can evaluate the compressor's function.
John
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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  #5  
Old 01-30-2007, 12:04 PM
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Location: West of Ft. Worth. TX
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John, He should have the more current system without the servo. We are talking about the W126.

On the heater, the rear seats should get their heat through ducts under the front seat, not the center console which is for a/c and fresh air.

A couple of system checks: Do you notice any changes in airflow to different ducts with different settings? If not you may need to resolder the boards in the ACC controller. (The joint where the boards meet in an "H" pattern.)

If you notice some changes but not from the correct ducts, then you probably have a couple of vacuum pods leaking. If you get nothing in A/C mode from the center vents, then you may just have a center pod leaking. With a leak there, and the way the ducting is set up, you probably won't feel much cold air anywhere. Check the vacuum pods with a mightyvac.
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84 300SD 350K+ miles ( Blue Belle )
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  #6  
Old 01-30-2007, 01:32 PM
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Welcome to the forum 81. I'm in the Phoenix area as well. North Phoenix actually and I went thru last summer with no A/C in my 240D. Not looking forward to this summer. Only thing I can comment on is that I think it's likely you wont be able to find a kit at Autozone.

- Peter.
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Formerly...
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1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
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  #7  
Old 01-30-2007, 01:49 PM
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Ok just checked, no matter what setting I put it on, the vents dont change. The only thing that changes is high/low/and auto air control, and when I push economy (EC) the compressor turns off. And the temperature of the air is as follows:

Drivers and passengers side - weak heat if heat is on, cool but not cold air if ac is on

Center front vent - pretty much no activity at all

Dash defrost output - medium airflow, again heat if heat is on, air is cool but not cold air if ac is on

Rear center vent - blows very hard, harder than any other vent, and the air temp does not change if heat/ac is selected. Always blows "room temperature" air.

Where could I get my freon checked? Can I do it myself or do I need to take it into a shop? If I have to go to a shop, does it have to be a mercedes dealership?

Thanks again, really wanna get this going before it gets too hot out
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  #8  
Old 01-30-2007, 03:01 PM
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Ok, It sounds like the monovalve is working. So let's concentrate on the ACC controller and the vacuum pods.
What usually happens to the controller is cracked solder joints. The boards are arranged in an "H" and vibration, time, whatever....causes the corner solder joints to crack. When you open it up, you will see what I mean. To remove the controller, start at the ashtray and go up. The wood panel has 2 screws underneath the edge. If you don't feel comfortable with a soldering iron, find a friend who is and it shouldn't cost you more than a burger or drink. Once that is taken care of, on to checking any vacuum pods that don't work.

I've noticed that it's hard to tell if the compressor and a/c system is doing its job until you get the vacuum pods working because the air is not blowing across the evaporator as it should.
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84 300SD 350K+ miles ( Blue Belle )
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  #9  
Old 01-31-2007, 01:25 PM
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Sounds good. Ill check it out first chance I get.

While I have the ACC controller out, could I do some modifying to the vent system? I NEVER use defrost on any of my cars, because well it is rare that there is ever any frost, and very little rain in AZ. So can I plug the vaccuum going to the center vents, and keep them in an open position at all times, and if I dont want to use the vents, use the manual open/close on the vents themselves?

In addition, could I do the same for the defrost, except keep them permanently closed because I never use defrost?

Seems like a much easier alternitive to isolating and replacing vacuum pods, while not taking away features of the car that I would normally use.
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  #10  
Old 01-31-2007, 09:38 PM
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From what I've seen on the set up of the air ducts, it really won't benefit you much to start plugging vacuum lines. The defrost is only one pod and really doesn't change the others. Also, the center pod switches between heat and a/c so it wouldn't be much help to plug that one either as vacuum actuates it to the a/c mode. On the W126 all of the pods are fairly easy to get to with one exception, the center pod. If you do a search of vacuum pod and my user name I've described how to take care of that one. Vacuum diaphragms are available at www.autoluxmbz.com for all but the long-throw (def. & fresh/recirc.)
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Sam

84 300SD 350K+ miles ( Blue Belle )
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  #11  
Old 02-01-2007, 09:37 PM
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Ok, got in there and the solder joints were ok. Some of the vaccuum hoses were bent, so by getting everything straight I am now able to get more air out of the center vents. Same issue though with no AC. The air out of the vents is room temperature. Is there any place I can check, such as one of the AC system lines, to see if its cold? So I can narrow down if its a problem with the ductwork or if its a problem with the AC system itself?

When I push anything other than economy, I can feel something kicking in and the engine runs a little harder, so it sounds like the compressor is kicking in.

Any thoughts?

Thanks!
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  #12  
Old 02-02-2007, 10:44 AM
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If you are getting air from the center vents, you should have the ability to get cooler air.

Also, you might try this: Inside the glove box, there is a plastic oval-shaped plug. If you pull this and with a flashlight, while the ACC is set at MAX. COOL., you should be able to see if the fresh/recirculating door is closing as you switch from EC to NORM.

To check the refrigerant, you really need a set of guages. What does the sight glass show you?
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84 300SD 350K+ miles ( Blue Belle )
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  #13  
Old 02-02-2007, 02:25 PM
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Ok thanks, Ill check the glove box and see if the door opens and closes. Now when you say pull the oval shaped plug, are you saying remove the glovebox or just open it? I cant look at the moment as im at work, but from what I recall, the only thing that is removable, is the glovebox light. But of course I have not looked into it much.

About the AC, ya I know I cant check the refrigerant, but im wondering if I can turn the AC on, enusre it runs for a little while, and then feel a line to see if its cold - so that I know if it needs recharged or if the cold air is just not making it to the cabin.

Thanks for your pointers Blue!
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  #14  
Old 02-02-2007, 02:35 PM
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Oh and sorry forgot to ask this, what is the sight glass? Is that to check the level of refrigerant in the system?

And where might this be located on a 81 300sd?
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  #15  
Old 02-03-2007, 06:14 PM
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Ok, had a shop check the psi on my system - low side was 45psi. From what im reading, that is about what its supposed to be at.

So the blower moves air through the middle vents, the system has enough r12 in it, and I can hear the compressor engage when I turn on the AC. What am I missing?

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