No matter what button I press on my climate control I get hot air from the window vent, side vents, and center vents. I have heard this is a default to defrost mode. Anyone know what is wrong, or where I should start?

It is a 300E, 1987.

This morning as I drove to work the air conditioner did work, with cold air blowing out of the center vents and the windshield vents not blowing any air.

So it seems sometimes it defaults to defrost mode, and sometimes it works well. Any suggestions would be appreciated.

Replace the fuse in your fuse box for air condition,fuse number 7. hope this help

------------------
MB STARS Master Guild Technician,12 years MB tech
6 years independent shop owner

Replaced the fuse just for kicks, no change.

When I hit defrost the windshield vents go full blast heat, as do the side vents.

When I hit full A/C or half A/C the windshield vents and center vents go to like a low heat. The side vents emit a slight amount of warm air.

When I hit economy mode the side and center, but not the windshield vents go medium heat.

This is all with the temp wheel turned as far cold as it will go and the fan on max.

The recirculation button makes no difference (not even sure what its supposed to do, anyone?)

So something different is happening with each button press. Im starting to think all I need is a recharge, what do you guys think?

[This message has been edited by Rick00 (edited 08-16-2000).]

Sounds like the heater control valve is not closing properly. Near the firewall on the passenger side. Believe it's vacuum controlled.

------------------
Jeff Lawrence
1987 300e
1989 300e
2000 Dodge Grand Caravan SE

Jeff, I cant seem to locate the valve. What does it look like? How can I check it? Or should I just replace it?

On a 124 chassis the valve is electrically controlled.It is called a mono-valve.A dealer should have a replacement mono-valve insert in stock.This site also may stock it, but I'm not sure.When you look for it follow the heater hoses to find it.You will see there are 4 small screws holding the insert in.Hope this helps.

If memory serves me correctly, the valve is located in the compartment with the battery, to the right front of the battery attached to the bulkhead with a bracket.

------------------
Jeff Lawrence
1987 300e
1989 300e
2000 Dodge Grand Caravan SE

[This message has been edited by jeffsr (edited 08-16-2000).]

Perusing the posts I have gotten a good idea how the pushbutton unit/monovalve system work, but some conflicting posts have me confused.

Basically, I understand that the monovalve is in the open position all the time, until the A/C button is pressed, then the monovalve closes, shutting off the hot water flow and thus the heat.

Now where I get lost is if the monovalve recieves power all the time to keep it open, and the A/C button cuts this power off, or vice versa, does the monovalve close when power is applied to it thru the A/C button?

Basically I want to test the power cable leading to the monovalve to see what the readings are. What should I look for? I am assuming power unless the A/C button is pressed, is this correct?

Also if someone could give me a ball park on what the monovalve does cost...

It's a 87 300E.

Don't remember which way the valve is controlled, but what usually happens is the rubber seal in the insert develops a hole. I would remove the insert and carefully inspect it.

OK I removed the monovalve and the rubber insert looks good as far as I can tell.

I checked the power coming into it. There are 2 leads. In Defrost mode both leads had power, while in all other modes only one lead had power. This is with temp wheel max cold and max hot. I am going to drive around today with the power disconnected just to see.

Anyone know what these readings point to? Are they normal signals sent from pushbutton unit? I dont want to replace the monovalve unless necessary ($145 for monovalve, no repair kit or insert listed).