No Heat, 560SL
 

Well, I haven't been around much in the last 6 months and that is because that the reliability of the old girl at 180000 miles is nothing short of phenomenal. This is attributed to this board and the locating of a good mechanic. We have a problem now, Houston and it is a little perplexing. I'll surely take it to someone who knows, but as you all know, I'm a freak about this car and need to know all I can about it!

Here is the deal:
Had heat yesterday AM on the way to the office. Went to lunch NO Heat! On the way home (2 hour trip)No Heat. Look I'm an old guy and by the time I got home I thought I would never walk again. Arthur must not like cold cabins.

I read RL's post on the search and it seems it could be two or three problems.
Clues: Over the course of the last year whether heat or AC every once in awhile the system would not function for about 5 mins. It would always come back on. I have noticed that I see very little difference in output between the 3 levels of heat and AC since I bought the car. I replaced the fan assembly last Summer and converted the system to current AC specs and dumped the old freon. (Poor AC, Hi cost for freon) I replaced the mono about two years ago

I have lights on the CCU no heat at all, no fan! What do you think fellas?

Am I heading for big dollars here? thanks in advance!

This might sound strange but
 

I sometimes have the problem of no fans. If i turn the ign. key CCW a little
the fans come on. I have no other problems associated with the key position.

I am not sure if it is a tumbler issue or the connector behind the tumbler.

Hopefully someone else here can give some insite.

Did you mean to say 180k miles?

Gary

The problem described above (jiggling to get the fan on) is definitely the ignition switch. The part isn't very expensive but it is a pain to change out. There are posts on this subject. This happened to me and it was one of the first things that I repaired.

Re the ignition switch issue--that's exactly what produces that problem, and replacing the switch unit itself is adequate; my indie did that, using the same tumbler assy and keeping the same key. Expensive in terms of hours as the cluster has to come out, which means the wheel comes off, which means the airbag comes out, etc. etc. I can tell you that there were no other symptoms to suggest the ignition switch--starting and running were fine, radio didn't go out, lights didn't go out, etc.

Re your problem, Tom--I'm no great expert but it sounds like something electrical has been going intermittent on its way to failing altogether, and the solder joints on the control unit (meaning the one with the buttons and dials) come immediately to mind, as does the potentiometer on the temp control dial--the latter especially if the fan's on but there's no ability to modulate the temperature of the air. My next area after that to consider would be the "brain" unit itself.

Thanks Craig!
 

Just to clarify! I am not getting heat nor is the fan running! as stated i replaced the fan this past Summer.

The control unit lights up and therefore power is running to CU. I checked the fuses and no go!

I hate throwing parts at things but I got a sneaking suspicion that we are going to need a new control Unit!

What say you?

"The control unit lights up"--are we sure that power to the lamps means there's also power in the control circuitry itself?

I had two problems last year causing no heat or fan.

1) Monovalve, You can just pull the 4 screws on top, check the diphraghm and replace if required.

2) Soldered on relay in control unit. Solder was detreiorated and needed to be redone. A very common problem with this car.

John Roncallo

Heat Issue!
 

Well, guys it needed a replacement of the control unit. Went ahead and replaced the whole thing.

My toes are once again warm. thanks for all the advice!

Tom,
Did you get a rebuilt or new one.
Glad you got it working.

Strife,
I took your advice and bought the switch. How do you drop the steering
wheel to get it out??? I took the 2 bolts out from behind the inst cluster
but the column won't budge.

Thanks,
Gary