heater problems - PeachParts Mercedes-Benz Forum

belowme · #1 12-09-2008, 04:57 PM

hello again,
]Its been a while and thanks again for making me smarter.
This time its my heater in my 1978 450 sl. the a/c, fan, vents all work well. The problem is no heat. Is it vacuum controlled? There is h2o in the system, no added in line valves and the selector switch in the dash works for every thing else. Please enlighten me with your wisdom.

TX76513 · #2 12-09-2008, 05:01 PM

I'll assume the coolant level is good. The heater valve is to be suspect and there was an upgrade valve. Look at the parts tab at top of screen and identify what you have for a heater valve.
(yes vacuum)

Deltacom · #3 12-10-2008, 04:41 AM

It would seem your heater valve is shut closed. As TX mentioned above it might be loss of vacuum at the valve or faulty check-valve. To establish this disconnect the vacuum pipe attached to the valve bell (at the nearest junction) and apply suction. If the valve opens (needs constant vacuum to stay open) it would imply loss of vacuum somewhere in your system. If applying suction does not open the valve then the diaphragm in the bell has perished. As a temporary measure you could tie the lever on the open position so you don’t freeze until you can replace the valve.

motu70 · #4 01-13-2009, 08:13 PM

I have a similar problem in my 1980 450 SLC. Can someone tell me the location of the heater valve and how to access it? Thanks.

winecountryone · #5 01-14-2009, 01:23 AM

The control valve is located on firewall.Follow the heater hoses from the rear of the engine.You must remove the heater box cover to access a hose connection on the inside of heater box to remove the valve.

I believe the previous poster has the operation of the valve incorrect.Vacuum is used to close the valve.The default position is valve open allowing water to flow through the heater core.If there is no heat the valve is probably either stuck closed or the heater core and/or valve is "gunked" up preventing coolant flow.

motu70 · #6 01-15-2009, 06:26 PM

winecountry i'm sorry but his is a stupid question. Where is the heater box located? I'm standing on the passenger side of the engine compartment. I can see the water pump and the left of that is a black square box. Is that it?

RadioTek · #7 01-15-2009, 11:13 PM

Heater box (actually the blower motor compartment) is the large black cover, approx 8 x 20 inches, centered under the back of the hood, in front of the windshield. A"stubby" screwdriver is your friend. The valve itself is on the firewall below the right side of the cover as you stand at the front of the car facing toward the rear.

Good luck

motu70 · #8 01-18-2009, 08:57 PM

radiotek,

here's a pic of what i'm looking at. I looked where you told me and it's just tubes and I didn't identify the heater valve.

RadioTek · #9 01-19-2009, 03:46 PM

Sorry, I didn't get the year on yours. It's much newer than mine. I think yours has the valve on the left side rather than the right (as you look at it from the front of the car)

motu70 · #10 01-19-2009, 03:51 PM

Sorry its a 1980 450 SLC. Its the same thing on the left side. There is that big black square thingy on the left with many vaccum tubes on top and thick black hoses on the bottom. The service manual calls it a "regulating valve". When I do a search in the online catalog for a heater valve it looks completely different. The mystery continues.