In my 560, I only have full heat all the time... even with the AC running. So, checked the monovalve insert first and there are no tears in the diaphragm that I can see. I suppose I can replace it as they are only about $45.

What are my next steps to check out? I believe the push button unit to be original to the car, is it possible it is not sending power properly to the monovalve?

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

I would check first if the monovalve is working.
With a multimeter you can see if the coil is ok (or just put 12 volt to the pins).

Sometimes the (very small) wires from the coil to the pins break.

Rob

You should probably sell that 560SELoL to me.

__________________
91 350SD
14 F150 Eco
19 Fusion Hybrid
11 GT500

Hm okay this is low on my list as the front end is trash, but I will take a brief peek when I start it up next month.



lol Wes. You stole that 300jestE from me.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

I'm not very good at giving mechanical advice, but i had a similar thing happen to me. i disconnected the mononalve from the ac control unit in the dash and connected it straight to the fuse box. When the key is on the monvalve engages and I can still control the ac from the dash control. It is temporary but it was so hot here I had to do it. I dont know if that helps but I gave it a shot. Here is a link to the post I got much help with. '82 300td AC question Help

__________________
Collector of Fine Hose Clamps
'77 240D 'AVA' is in heaven now
'80 240D Kanarienvogel
'82 300TD 343k was my daily driver 'ADOLPH' In Surgery for a severe Deer Bite to the Nose
'88 560SL 102k 'White One'

I had a similar problem, see my threadI believe your controller is similar to the W124.
1) Check your mono valve as advised
2) Check voltages at the connector when the knob is turned at both max and any middle settings.

I have to recheck the duovalve because I replaced it before testing. If not the valve, I suspect a bad knob rheostat at middle settings or bad cabin temp sensor as suggested.

__________________
'88 300TE, 175k, black RENNTech 3.6L Recaro C's AMG 1 SOLD
'92 500E, 110k, Spruce green, stock SOLD
'94 E320 Cabriolet, 130k, E500 wheels, Emerald green SOLD
'94 E320 Cabriolet, 110k, black, stock, SOLD
'88 300TE, 229k, dark grey, SOLD
'90 300CE, 212k, white, new paint, SOLD
'91 300E, 209k, white, rebuilt head SOLD
'74 914-6, grey, 2.7L 325hp twin turbo Audi conversion