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Discussion Starter #1
My 1980 300D is having a climate control nervous breakdown. After resurrecting the climate control system - new compressor, replace/repair ALL vacuum actuators, lines, connections, etc. over a year ago and enjoying working heater, air conditioning, amazing myself and friends that the system worked so well, turning on the AC compressor yesterday brought forth hot air with almost no fan action, turning on the heater turned on the AC with full blast fan, turning on the defroster supplies hot air and fan blast (as usual). Comical yet not so much as the dash will have to be taken apart again, etc. Anyone else have same symptoms? Does this indicate fouled up 'brain' behind glovebox or fouled up climate control panel on dash center panel? Or both?
 

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I'm not familiar with the 'brain', and it doesn't really sound like the CCU, that I've experienced, yet maybe it is the issue. Sounds like you're going to have to pull one or both to inspect for cold solders.
Also check the pipe that leads to the inside temp sensor, located behind glove box, made of foam.
 

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Don't know how deep your pockets go but you might want to look at this site it's interesting anyhow.

UnwiredTools™ ACCII-VC Upgrade Kit


New Version!


Now with a billet aluminum vacuum connector. Easy installation and excellent temperature regulation! The UnwiredTools™ ACCII-VC Upgrade Kit replaces the unreliable OEM analog and mechanical climate control system with modern digital microprocessor technology. This upgrade replaces both the OEM Servo and Servo Amplifier.

The latest version of our popular climate control system eliminates the need to splice wires, calibrate the temperature wheel and feed temperature probes under the dash. It even offers higher precision temperature regulation than ever before!

The ACCII-VC version features a high-quality aluminum billet vacuum connector which mates with your vehicle's vacuum system connector, making installation a snap. This version is highly recommended if you're doing the installation yourself.

Like all UnwiredTools Automotive products, a Five Year Warranty is included.



UnwiredTools, LLC.
 

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Sound like you have abad servo, don't replace it with the digital upgrade just use the plain ol' ACC servo found in 1980 and lower cars.
 

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You can get a rebuilt servo from George Murphy at performance analysis for around 500 dollars. All new parts and an aluminum base are used, so no more cracking plastic. The plastic cracks and coolant leaks into the servo internals, fries it. I was watching an aluminum rebuilt servo on eBay, it went for 300 dollars, deals can be had on these, so look around.

On my 1980 my servo is cooked and also the push button unit only works on defrost. The servo is bypassed for heat. A weird thing is when my push button unit isn't left at the OFF position the engine does not shut off. The entire CC system was replaced in the 90's with 24 hours of shop labor, all diaphrams and other stuff. Maybe the push button unit itself has a crack in it, or I have another ruptured diaphram? Problem is that there aren't too many people familiar with this system. (Except George Murphy)
 

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Discussion Starter #6
Thanks for all the replies. The servo in the car is an aluminum bodied George Murphy unit, that's why I figured the nervous breakdown has been caused by something else. My engine starts and stops with the climate control in any position. If the engine won't turn off with climate control engaged some sort of vacuum leak must be lurking.
 

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Even though it is alum. bodied doesn't mean that the electrical part of it is working properly.
 

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That's a bad servo....

It's less money to get the upgrade because you'll need to buy a new servo amplifier if you replace the servo. The aluminum vs plastic body doesn't address the problem. The problem is that the original servo design isn't reliable. The vacuum distribution "puck", the feedback potentiometer, the drive motor, and the water valve are all connected by a vertical shaft. If any of these mechanical parts fail (and they do) then the entire system is kaput. Oh and yes the bodies do leak. The leaking is improved a bit by the aluminum body but the design is still the same junk.

The upgrade works well because the hot water control is moved to an easily replaceable water valve from a 201 chassis. The other functions are by an electronic controller which won't wear out.
 
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