No Heat - Temp Blend Door?

[vladimirhtg]

I've got an interesting one:

My 318is has very limited heat right now. My temp control knob will turn to the cold side no problem, but I can feel resistance when I get to the hot side.
From reading, it sounds like that temp control knob is connected to a "blend door/flap" that controls air flow between the two sides.
I do feel warm-ish air that comes out of the foot vent only. None makes it to the upper vents. Perhaps the windscreen vent, I haven't checked. I can do more testing if it helps the diagnosis.

I did the R134a AC swap (including removing the evaporator coil completely), but I think that's the only work that's been done in the region. Well, I also bypassed the relay under the driver's side dash, but that was fairly non-invasive.
Could I have knackered something when I was down in the area? Can anyone point me to this 'blending flap' so that I can check for blockages or something that would cause it to not open completely?
I've read about the solenoid valve that controls coolant flow. That is always suspect, but I doubt it's the issue since I can feel warm air in the foot well.

I'm just now getting to Fall weather in good old SC, so I've got a few weeks to get it figured out.
My descriptions are a little old because it's been four or five months since I actually tried to get hot air from the car.

[Das Delfin]

A few things:

- the car has to be up to operating temp to get hot air

- physical resistance in the temp knob is not normal

- the temp knob sends an electric signal to the hot water valve and simultaneously operates a bowden cable that opens or closes the mid-level temperature blend flap.

- the temp control has to be set at 100% hot to get warm/hot air from the mid vents, though the footwell and defrost are directly related to the placement of the temp dial

- if the dial isn't at all the way hot, there should be a temperature difference between the mid level vents and the defrost and footwell. The defrost and footwell should be hotter than the hand vents. The idea behind this system is to keep the inside warm while directing cool air at the drivers face to prevent fatigue.

Take out your radio and possibly radio faceplate so you can see the bowden cables. Maybe your glovebox and some of its trim panels too. Undo the temp bowden cable and see if there's rust on the inner cord. Check to feel where the resistance may be coming from. You should be able to trace it to where it connects to the heater box. If you can remove the whole thing you should be able to isolate whether the cord is bad or the blend flap is obstructed or its action needs to be adjusted. My guess is something got bumped out of place during your evaporator replacement.

[jeffnhiscars]

When I changed my evaporator I shoved the temp sensor through the fins. Being soft, the probe deflected and blocked the blend door. Best practice is to shove a rod through the evap end plate to make a path for the probe.

[Das Delfin]

^ that's interesting, but an electrical sensor wouldn't cause this:

My temp control knob will turn to the cold side no problem, but I can feel resistance when I get to the hot side.

[jeffnhiscars]

thats exactly the problem I had all winter. The dial would only go 3/4 to hot...until I pulled the probe, reamed a new straight hole with a long phillips head screw driver then replaced the probe with a straight one. The deflected probe physically stopped the blend door from closing all the way because I mistakenly thought the probe was rigid enough to go through the fins in a straight line