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  #1  
Old 10-12-2007, 06:39 PM
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Question Question about replacing AC/Heater controls for 1983 300D

Folks, my AC/Heater button unit lately has caused my AC to stop intermittently. I can be driving, with nice AC, and all of the sudden, hot air will be blowing out of the vents. I can hit the stop button, then hit the AC button, and the AC will then start up again.
I'd like to replace the AC/Heat button unit. I have recently purchased one used, and was wondering how difficult it might be to replace? I don't see a way to remove the wooden trim panel around this unit - How do you remove it? Is it a simple matter of just unscrewing the old one, and plugging in the new one, or is there something else that I need to watch out for? While I have it out, I'd like to make sure that the controls light up, as they don't in my current unit. Is there some sort of bulb back there that needs to be replaced, that feeds a fiber optic harness of some sort, or are there bulbs in the AC/Heat button unit?

Thanks so much in advance!

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Old 10-12-2007, 07:01 PM
Craig
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It's pretty simple to replace, the wood trim comes off (I think you need to remove the ash try first), then unscrew the plastic cover and the unit slides out. There are a couple of electrical connectors and the unit is lit by about 4 small bulbs the back. It's all pretty obvious once you get it apart. If the bulbs are burnt out, check your local auto parts store (make sure not to get higher wattage or you will melt the little light fixtures.
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Old 10-12-2007, 07:35 PM
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I had a similar problem with my '83 shortly after I bought it. It was the evaporator temperature switch. Remove the right side kick panel to gain access to it. It can be jumped out for testing purposes, but continued operation like this may cause your evaporator to ice up.
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Old 10-12-2007, 09:51 PM
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Thanks, folks, for your replies. I was wondering if you might be able to tell me HOW the wood trim comes off? I see no screws, nor any other fastener available from the front. Just exactly how does one remove that wood trim?

Thanks again!
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Old 10-12-2007, 10:01 PM
Craig
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The trim just gently pries off, just pull and wiggle it around a little after you remove the ash tray. Don't force anything, it should come loose.
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Old 10-16-2007, 02:07 PM
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Question

Guys, sorry, I would really like to understand what holds that nice piece of wood trim on - Let me see, I remove the ash tray, then I'll take a small flat-tip screwdriver and GENTLY pry around the wood trim, and it should pop out? What holds it in? and what do I do to reinstall it? Is it held in by some sort of clip?
I hope to receive my new climate control assembly this week, and thus would like to disasemble this in preparation, but I want to ensure that I can put that wood trim back on, as it is a really nice looking piece of wood trim, and I don't want to mess it up.

Thanks so much for further explanation!
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Old 10-16-2007, 02:22 PM
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No clips. Nothing complicated. Just pry it off and you will see some pins on the back. It just presses back on when it's time to reinstall.

Have you excluded the evaporator temp regulator as cause of your problem?

Quote:
Originally Posted by rfdillon View Post
I can be driving, with nice AC, and all of the sudden, hot air will be blowing out of the vents.
Heated (hot) air or ambient air? Does the compressor remain engaged or does it disengage?

Last edited by tangofox007; 10-16-2007 at 02:50 PM.
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Old 10-16-2007, 03:03 PM
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There's an excellent article on the whole process in the DIY section under 'climate control' . I don't know how to direct you with a link but if you'll check it out it will take you step by step through the whole procedure.
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Old 10-16-2007, 04:23 PM
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Angry

The symptoms I have are this: Some times I can be riding along and the AC is blowing nice and cold (I have measured it at 48 degrees F when it was 90 outside), and all of the sudden, instantly, I have hot air blowing out instead of cold air. And it is real hot! This morning, I had nice cold AC, but when I got to the car to go out at lunch, it would only blow HOT air, and regardless if I turn the AC on, off, hold in the AC button, etc., I cannot get it to blow cold air.
I am stumped, but I do hear the compressor come on when I push in the AC button. I replaced the monovalve a few years ago, so I don't think that is the problem, and am hoping that replacement of the button control unit will fix it.

I really appreciate all of your advice and help!
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Old 10-16-2007, 05:08 PM
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If the compressor continues to run during the hot air episodes, the evap temp regulator can be excluded as the culprit. I would check the electrical connector to the monovalve. If the monovalve loses power, it opens to the full heat position.
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Old 10-16-2007, 05:12 PM
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My sd started doing something similiar. Check the plug on the compresser. I had to wiggle mine a bit. Take it off, put it back on, make sure you have good contact.
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Old 10-16-2007, 05:17 PM
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Quote:
Originally Posted by rick surgent View Post
Check the plug on the compresser.

That will turn the cold air off; it won't turn the hot air on.
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Old 10-16-2007, 09:11 PM
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The compressor runs, but all I get some times is hot air. For example, this morning, cool air. Lunch time - hot air. On the way home this evening, cool air. Got into the car at the mall, all the way home, hot air.
Does anyone have any specific wires, or things to check on the monovalve? I looked at it today, and it was plugged in and the connector looks ok externally (no frayed or broken wires)
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Old 10-16-2007, 10:48 PM
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Quote:
Originally Posted by rfdillon View Post
Does anyone have any specific wires, or things to check on the monovalve? I looked at it today, and it was plugged in and the connector looks ok externally (no frayed or broken wires)
The connector on the monovalve can look fine but still not be making good contact. I have seen them loose contact when they get warm. You might try cleaning the contacts and maybe roughing up the female connections a bit.

Also, maybe the next time you have the "problem," disconnect the monovalve and see if the air gets any hotter.
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  #15  
Old 10-17-2007, 10:41 AM
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I jiggled the connection around this morning, and the AC worked fine (but that is no sign that it is fixed, as it has been very intermittent). This evening I'll pop off the monovalve connector and use some steel wool to polish things up a bit on the connector and the monovalve, and see if the intermittency gets better. By the way, I did try one thing on the way to work this morning; I had the AC blowing and moved the heater temperature control wheel to hot, and it blew out hot, then moved it back to minimum, and the car cooled down, so that wheel apparently is working (today).
Thanks again for your help!

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