heat at heater core but not at vents? - PeachParts Mercedes-Benz Forum

Jarod · #1 09-03-2010, 09:34 AM

Sooo, took my benz off the road due to an issue i had a few years back with no heat, drove it in the summers, and my other car in the winter. so now my lil black saturn is dying (figures) so i'm wondering what is wrong with my heat again.
heres my post from a few years back:

I get heat at the heater core inside the car, just no air circulates past it.
I have removed the glovebox insides, and I can see the recirc/vent vacuum pod, and a pink vacuum pod that moves a linkage, but that doesn't seem to actuate anything.
Should this pink vacuum pod be moving something?

Is the pink pod the heater "door" control?

Thanks,
Tom

Only things id like to bring out differently is i can reach up where there are some brass/copper lines (I'm assuming thats the heater core) and those definetly get very hot when the car is warm, but i get no heat from the vents. i would like to disassemble as much of the blower motor/ductwork as possible just because the scent seems to indicate a mouse nest in there...

Got any ideas on whats wrong with the heat? any suggestions on removing mouse remnants? i'd like to avoid removing the entire dash as i've read about having to remove the windshield...

Thanks,
Tom

micalk · #2 09-06-2010, 02:03 PM

Sorry, don't have 116 specific info, but on a 126 (81 300SD)...

There are two pods connecting to the main air flap. When the ACC is off, vacuum is routed to the pods to completely close the main air flap. When the AC is on but temp wheel is not min temp (not max cooling) there is no vacuum routed to the pods for 100% fresh air, and 20% fresh air when the temp is set for min temp. With access to the pods you can connect your MityVac to the pods to see if they operate with vacuum.

But this probably isn't your problem. The flap should only determine if outside air or inside air is pushed through the system. The rest of the flaps route the airflow to the specific vents. When in defrost, all the vacuum pods have no vacuum to them. It's a default mode. And I'm assuming your fan is working, yes?

Do you have defrost when the heat is on? if so, then you need to check the operation of your switchover valves. A strong vacuum leak might cause this symptom (may cause problems shutting off motor). Check to see that there is voltage to operate the switchover valves.

My recommendation: Check the main vacuum line to the switchover valves when everything is off. It should hold vacuum. Then check the electrical operation of all the switchover valves, and that the pods they operate all move and hold vacuum. If they all work and your vacuum lines are sealed properly, then you need to check the operation of the control unit.

Do you have a Climate Control Manual for your car? I can help you with 126 diagrams which might be close - otherwise you'll have to depend on the kindness of others.

Jarod · #3 09-07-2010, 10:02 AM

we had a fight with it this weekend, the flaps are indeed working, my issue resides in the "evil servo". the gears were seized up, so simple solution, un seize them and it'll work again right? WRONG.

it very happily closes the valve every time the wire is connected to it. i dont know what controls it, or how it knows what position its supposed to be in but it thinks fully closed is correct.

i do have heat since i unplugged the evil servo and applied power directly to the motor to move it into the "heat position" so I'm not freezing anymore.

I've looked at the climate control manuals and stuff a bit (w116.org has the manual for this car) but I'm going to have to do more reading and figure out how this contraption works, or failing that install a 1/4 turn valve in place of it... lol

rrgrassi · #4 09-07-2010, 11:36 AM

You can get an aluminum bodied servo, and IIRC, there is a digitally controlled version out there as well.

My '82 does not have the servo set up.