Heat/ Please 87 300SDL

[tenmaz]

At startup I have heat. When driving it cools. I disconnect CCU I have heat at defrost so hot I open windows. I reconnect a different CCU. I test interior temp. sensor for resistence/ test ok. Temp sensor at heat exchanger behind ashtray is taped in so I disconnect electric connection/ hot at startup then cools whiles driving. I did not remove heat exchanger temp sensor and did not do resistence test yet!!! Could it be the heat exchanger temp sensor ?? Or what else might it be??? thanks for any advise
? does disconnecting CCU and having heat eliminate monovalve from consideration

[sixto]

If you have heat at idle but not when the car's moving then most likely you need a new monovalve cartridge.

Sixto
93 300SD 3.0

[Brian Carlton]

Originally Posted by sixto

If you have heat at idle but not when the car's moving then most likely you need a new monovalve cartridge.

Sixto
93 300SD 3.0

If he's got unlimited heat with the CCU disconnected, the monovalve diaphragm is probably ruled out.

[sixto]

Good catch. I was thinking that even a bad monovalve allows heat when the car's not moving. I don't understand it but that's how it was on my 300SE. New cartridge fixed it.

tenmaz, remove the electrical connector from the monovalve and go for a drive. If that gives you heat at speed then then a monovalve cartridge won't help.

[edit] Oops, you already did that.

Sixto
93 300SD 3.0

[Brian Carlton]

I'm a bit baffled by it, actually.

Two different CCU's and a cabin temperature sensor that checks out...........

Wonder if the aux. pump is causing any issues? I had to disconnect it on the SD because of loud cycling noises from the monovalve. Don't think the SDL is wired the same way however.

[SD300]

While on the subject of heat, I have a 81 W126 300SD, the heat cannot be turned off, so where do I look for the valve to shut off. It would be nice to be able to shut off heat during warmer weather.
TIA

[Brian Carlton]

Originally Posted by SD300

While on the subject of heat, I have a 81 W126 300SD, the heat cannot be turned off, so where do I look for the valve to shut off. It would be nice to be able to shut off heat during warmer weather.
TIA

Turn the temperature dial all the way down to the lowest setting (a/c) until it clicks. What happens to the heat?

[SD300]

Brian
The last owner said the valve cannot be turned off.
Is it the little solenoid infront of the firewall got stuck open?
or is it hidden under the dash some where the sun doesnt shine?

[Brian Carlton]

Originally Posted by SD300

Brian
The last owner said.........

I'm really not interested in what the last owner said...........

[sixto]

The monovalve stays open by design. It's the job of the CCU to close it when cabin heat is not desired. If the monovalve isn't getting +12V through one pin and a solid ground through the other pin, it's going to get hot inside the car.

Sixto
93 300SD 3.0

[captainmonk]

it gets warn in BC?

[jfikentscher]

I have the opposite problem. I get heat and temp control while driving, but at idle the heat goes away. Also have quit a bit of gurgling in the dash area.

[SD300]

Originally Posted by jfikentscher

I have the opposite problem. I get heat and temp control while driving, but at idle the heat goes away. Also have quit a bit of gurgling in the dash area.

Sounds like u have air trapped in the system. And your coolant is not top up.
There should be a small elec pump that keeps circ going when idling. Some kind of ingeniuos Mercedes design, most cars dont need that.
Just more issues pop up when the car reach the sunset years.


BC borders I'll ask her( Alaska) and Washington, so it can be warm n cold.
A few days during the summer we may need A/C running too, thats only if u can afford one.
We only had color TV a couple yrs back. Perhaps we should call us Cuba of the North.

Where is the Monovalve located in the car?

[captainmonk]

i guess if i was in port angelos i could wave at you

[SD300]

Port Angeles is not quite close enuf, been to the San Juan Island not far away from there. A major historic out post, one time the border dispute was happened there, there is an American camp and Canadian camp. A fight was broke out over a lost pig, luckily no one was hurt over the incidence.
Few yrs later the Island was given to US as ruled by International Tribunal.

Some parts of Canada looks south of 49th parallel.
ie Van island, and most part of southern Ontario.
Now with passport when crossing border, is becoming a real pain. Only applies to Air traveller, next yr will need it for driving or foot visitors.

One part of Vancouver is called Point Roberts WA, is off Van, used to go there for XXX movies and drinking on Sundays also cheap gas too.