1980 300D heater and other questions

I have a 1980 300D that generally runs well. I am having a few problems that I'm hoping this group can help me diagnose. The most urgent one is the heater issue.
1. The heater works intermittently - it may or may not blow hot air. The blower always works and the air is always directed where it should be (vents or defrost). The heat also blows all hot or all cold. The thermostat does not appear to have an effect. From reading NG history it sounds like the probably is most likely with the amplifier(?) behind the glove box. Does this sound right?
2. Dash lights are not working. The lights to the center console quit working several months ago, and more recently the dash lights quit working. I read today about squiring some contact cleaner into the dimmer switch and will try this tomorrow. If that doesn't help, is it most likely a wiring problem (loose wires or cracked solder joints)? Is this something somebody with modest mechanical skills could fix?
3. Door locks have slowed to the point of not working consistently. Sometimes the doors will lock, but I have about a 4 second window after shutting off the car to turn the key in the door. This seems like a vacuum problem. I've read that this can cause other problems (trans, failure to shut off engine) but I'm not experiencing either of these. Is this most likely a leaking in a hose or a door lock? If so, it is reasonable to try and fix myself?
4. A/C quit working last year. It worked fine right up to the point that it started making a horrible noise when I turned on the A/C or the defroster. I assumed it was a bad compressor or a clutch to drive the compressor. The mechanic said that he didn't even want to look, as it was likely a $1000+ problem to fix. Could possibly fix it more inexpensively by installing used/rebuild compressor and then get it charged with freon? Is it likely a bigger problem than that?
Thanks for any help.
Rip (email address has been modified to minimize spam)
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snipped-for-privacy@hotmail.com (Rip D.) wrote in message

The amplifier and servo system are only used in cars with automatic climate control. Usually when either of these fails, you wind up with the system stuck and unresponsive, as the servo controls the blower speeds, where the air comes out, flow of hot water through the heater core, etc. If you can get the air to correctly come out the bottom vents for heat, the center vents for cooling, the windshield vents for defrost, the amp is not likely the problem, as it is at least driving the servo motor back and forth and moving it. Could be a bad servo. One failure mode in the servo is for it to crack and start leaking, with the water then going into the internal electical partss. So take a close look at it. It's on the right hand side, near the firewall, grapefruit size widget with four water hoses, two elec cables and bunch of vacuum hoses connected to it.
If you have a regular heating system, then sounds like the problem may be the valve that regulates water flow thru the heater core. To lose heat can also be a symptom of low coolant.

I've noticed the dimmer switch on my 300SD has some bad spots on it. If you rotate it, it tends to go out, instead of dim. I haven't tried contact cleaner, but I would think the big problem is getting the cleaner into the actual switch, I'm not sure that would be possible without removing the instrument cluster. Fixing your light problem is easy from an electrical standpoint, but very difficult from the standpoint of pulling the dash apart to find the actual problem. I'm assuming you checked the fuse?

Could be a leak anywhere in the system, including a bad servo if you have climate control. Could also be a failing vacuum pump. As far as eliminating the likely possibilities, perhaps someone else can point you in the right direction.

Sounds like you need a new mechanic, as an initial diagnosis shouldn't be difficult. If it's the clutch, then it is relatively cheap to fix. If the compressor failed and contaminated the whole system with metal fragments, it is going to be expensive and the $1000+ figure could be conservative. At that point if you're going to fix it, you will likely want to convert the system to R134A refrigerant.

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I have an 82 240D with simular problems or have had these in the past... In which im looking for a new thermostat, can someone guide me to the one i need my car wont get above 50c in cold weather. i looked for thermostats for this car and i get like 20 different things. some help?
your door lock problem is likely a vaccumm problem.. i tried troubleshooting this and got all 4 doors working but then the fuel door would remain vaccummed locked. in the end, i capped them all off (golf tees work really well for plugging the tubes).
a new ac system on a w123 (aftermarket parts, new) is around $300 for the compressor, clutch and other needed parts. my ac does not work, if you leave the switch off the car will stall and die, if you leave it on (although it doesnt work) it will function fine.
these are all projects im currently working on fixing. today i ordered new weatherstripping and hope to begin fixing the ac very soon.
the parts for these cars are reasonable in my opinion, paying a mbz mechanic to do work on 20 yr old car is VERY EXPENSIVE. i reccomend the DIY route, and if you cna find a mechanic who is willing to be a technical adviser (i have mine do the valves and filters when needed and i can ask him about anything and he will tell me how to fix and diagnose problems).
maybe this will help a little.
-mitch
snipped-for-privacy@hotmail.com (Rip D.) wrote in message

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