Climate Control Problem

[xkeots]

Hi All,

I am finally using my 1980 450 SL with 63,000 mi as a daily. When I bought it I knew that the a/c compressor clutch was shot. I was told that when I was ready, to change the whole compressor as it costs about the same as the clutch. I have no belt on the compressor now as the clutch rings were spinning out of round and hitting wires and other close in proximity things.
I am also getting continuous hot air from the lower outlets with the temp control in the lowest blue spot and it doesn't go off (really is a drag when it is 80 outside). Do I have another problem to look for besides the a/c compressor?
The car itself runs great..

Thanks for any help

Jack
1980 450 SL

[ScottinSoCal]

Originally Posted by xkeots

I am finally using my 1980 450 SL with 63,000 mi as a daily. [...] I am also getting continuous hot air from the lower outlets with the temp control in the lowest blue spot and it doesn't go off (really is a drag when it is 80 outside). Do I have another problem to look for besides the a/c compressor?

Your ACC servo and amplifier are shot. Look in the engine compartment on the passenger side up toward the passenger compartment. You'll see a short, black plastic tower there with a lot of vacuum and electrical connections going to it. That's the servo. It controls the heat and vents in your car. The plastic body on it will crack and it gets stuck in a single mode - in my case max cool, in your case heat. That will need to be replaced, and it isn't cheap. I'd suggest a rebuilt with a new aluminum body. That eliminates the most common failure vector on the part and it'll last longer. It's an easy DIY repair after you've spent the ~$500 for the new servo.

For the amplifier, look under the dash on the passenger side. Near the center console, mounted upright there's a little box about 4" square and 1" thick. That's the amplifier. Two screws and a push-on wiring harness disconnect it. Don't replace this until you've replaced the servo, because a bad servo will fry it. It costs about $120 and is available from several places.

I can give you a couple of leads on where to get replacement parts, if you need it.

[ScottinSoCal]

I guess I should add:

The place that advertises here (unwired tools) has a digital replacement for the servo and amplifier. It costs more (about $700), it didn't look like something I could install myself when I read the directions and I couldn't find anyone who has installed it, but it's supposed to improve the operation of the system, and it would last a lot longer than a replacement servo.

Mine is operating at 100% (for a servo/amplifier system) and it's slow to react to temperature change, not very sensitive, and I don't expect it to last more than a few years. I figured I'd replace the servo with a digital then, after I'd gotten the rest of the car to where I want it and knew more about the system. I could probably do it now, after I've had to go through the system and figure everything out, but I couldn't have when I started.

[smallblock450sl]

When I got my 78 450sl, had nothing but "cold air" blowing. I got lucky! A vacumn line and (because i have a small block chevy engine) some heater hose rerouting. All works great now. I looked into posts from people that had made the conversion and if I ever had a "climate control system problem" again, I would go the the digital way. look at Performance Products.. They sell the kit at (699.00 I think) and 15% off right now. I have also seen them on Ebay for "Buy it now" for 475.00. By the way...You can download the installation instructions at Performance Products or Unwired Tools. You know the addadge......You can pay me now...Or pay me later. I like doing the job once and if an upgrade is better.Go for it. Good Luck on your project.

[Richard Wooldridge]

I installed the digital servo in my '79 450SL, and it only took a couple of hours to install. What took the time for me was finding all the leaks in the vacuum system - I finally just plugged off a couple of flap diaphrams to get it working, as they were leaking and I didn't want to take the dash apart. I installed the digital controller inside the cabin in front of the glovebox, and pulled all the wires and vacuum junk that was on the old servo inside the cabin as well, leaving only the two vacuum switches and the water valve outside in the engine compartment. It looks real clean now, and controls the temperature very well.

[xkeots]

Originally Posted by ScottinSoCal

Your ACC servo and amplifier are shot. Look in the engine compartment on the passenger side up toward the passenger compartment. You'll see a short, black plastic tower there with a lot of vacuum and electrical connections going to it. That's the servo. It controls the heat and vents in your car. The plastic body on it will crack and it gets stuck in a single mode - in my case max cool, in your case heat. That will need to be replaced, and it isn't cheap. I'd suggest a rebuilt with a new aluminum body. That eliminates the most common failure vector on the part and it'll last longer. It's an easy DIY repair after you've spent the ~$500 for the new servo.

For the amplifier, look under the dash on the passenger side. Near the center console, mounted upright there's a little box about 4" square and 1" thick. That's the amplifier. Two screws and a push-on wiring harness disconnect it. Don't replace this until you've replaced the servo, because a bad servo will fry it. It costs about $120 and is available from several places.

I can give you a couple of leads on where to get replacement parts, if you need it.

Hi,

I am not sure if you got my problem here. When I push the buttons on my Climate Control the air goes to what ever button I push the defroster (etc) and where it is supposed to. When I put it to off the fan shuts down. I have no a/c compressor connected so I am only getting hot air. I am getting a small amount of hot air coming out of the lower dash with it in the off position. The servo is the big box on the passengers side engine compartment. Maybe I should change the a/c compressor and get the rest checked out before I start throwing money out.

Jack