Why heater never gets hot - PeachParts Mercedes-Benz Forum

netboy · #1 12-15-2010, 03:11 PM

My 83 SD heater works but will not blow hot air, only warm. The T-stat has been altered to run cooler so it operates at 80c highway in 5 degree OAT with radiator partially blocked. At 80c it only blow moderate heat on defrost and blows around 60f (much cooler) out the vents when the button next to defrost is selected. Why does it not blow the same temp out the vents as at the defrost. I have wired the fresh air pod closed. I let it idle for an 8 hr period because of a extremely cold and remote location and it was only luke warm when i got back to the car. The monovalve works but doesn't effect the temp plugged or unplugged. I assumed all the air blew through 1 heater core and was directed by pod selection to desired location.

compress ignite · #2 12-15-2010, 06:14 PM

'Clogged Heater Core.
(Yadda,Yadda,Yadda)

Mainly,you've altered the Factory Specifications for the Engine Cooling/HVAC
operation.

This car was engineered/built to operate in the Great Frozen North that's Deutschland.
('Ain't No Winters in them Tennessee Hills 'Near as Cold).

Restore the Cooling system to factory Specs and the problem will disappear.

Final Rant:
Letting a Mercedes Indirect Injection (Pre-Chamber,Glow Plug equipped) Idle
for long periods of time will "Coke/Carbon Up" the Pre-Chambers and Engine.
AND Shorten the Engine's Lifespan Substantially!

netboy · #3 12-15-2010, 08:09 PM

Quote:

Originally Posted by compress ignite

This car was engineered/built to operate in the Great Frozen North that's Deutschland.
('Ain't No Winters in them Tennessee Hills 'Near as Cold).

It was 9 degrees this morning. 80c op temp should produce sufficient heat to heat cabin.

Restore the Cooling system to factory Specs and the problem will disappear.

That will not make one temp come from the defrost and another from the vents.Thanks for your input.

Final Rant:
Letting a Mercedes Indirect Injection (Pre-Chamber,Glow Plug equipped) Idle
for long periods of time will "Coke/Carbon Up" the Pre-Chambers and Engine.
AND Shorten the Engine's Lifespan Substantially!

I'll risk it.....being 20 miles from nowhere with a -5 wind chill.

Brian Carlton · #4 12-15-2010, 09:06 PM

Quote:

Originally Posted by netboy

At 80c it only blow moderate heat on defrost and blows around 60f (much cooler) out the vents when the button next to defrost is selected. Why does it not blow the same temp out the vents as at the defrost.

I've been into the system on the SD in a big way and I'm currently struggling with the exact same issue.

I get moderate heat from the defrost vents and the side window vents (run by the defrost pod) but cool air from the center vents. In theory, I should not get anything from the center vents.

Be assured that the center vent pod works perfectly and holds vacuum. If I put vacuum to the center vent pod and open it, the temperature of the air from the center vents climbs dramatically and will probably match the defrost temperature.

I need to do more research to try to figure it out............I should have no air from the center vents in the winter............but, clearly, the SD has other ideas.

The system is far more complex that is apparent on first observation.

netboy · #5 12-15-2010, 09:28 PM

I know.... only cold a/c air should come out the upper vents and warm out the foot vents with the same button (2nd). From experience, I'm sure it is a vacum problem. Could possibly be a vacum rail malfunction.I'm going to test the floor pod tomorrow, maybe even wire it open as long as I still get defrost. What side of the console gives access to the center pod?

Brian Carlton · #6 12-15-2010, 09:44 PM

Quote:

Originally Posted by netboy

I know.... only cold a/c air should come out the upper vents and warm out the foot vents with the same button (2nd). From experience, I'm sure it is a vacum problem. Could possibly be a vacum rail malfunction.I'm going to test the floor pod tomorrow, maybe even wire it open as long as I still get defrost. What side of the console gives access to the center pod?

You can access all the pods via the switchover valves. Remove the passenger side kick panel and carpet. Carefully remove the carpeting on the right side of the transmission tunnel. The six valves will be apparent next to the CCU. Remove the valve group and you can access the individual lines that extend horizontally from each valve.