elementsix

I have a continuing problem with the lack of heat in the cabin. Hopefully you might be able to advise me on it so I can get some heat back into the cabin!

I'm now convinced the problem is 'frozen heater flapper boxes' as referred to one time by 'Adrian'.

I understand that the flaps are controlled by differential pressure - I think this means that if you open the flaps (2 and 4 Servos in the front boot) you are creating an area of lower pressure and the air comes forward to the cabin instead of going to the wheel-wells?

Servos 2 & 4 closed the pressure in the system builds-up (as the air is not wanted in the cabin) and must vent somewhere, so flaps then close and shoot-out the wheel vents?

Question is - how do you unfreeze these rear flaps?


Shane
1991 C2 Cab

JasonAndreas

Have you removed the top of the front mixing chambers to look at the position of the temperature control doors? You can't just trust what you think is the correct position of the servos as myself and too many others have discovered.

All Heat


All Cold


If you start the car, turn the CCU to recycled air, turn the car off (make sure the windows, passenger side door and front trunk are closed) and then the slam shut the driver's side door do you hear a clicking sound coming from the rear? The flaps normally rest in the down position which is full heat to the cabin and I would think that is where they would stick because of corrosion. To unstick them you need to remove the orange heater hoses that connect the heat exchangers to the flapper boxes and just tap the doors. (I can post a photo after I go and buy some new camera batteries.) If the flaps were stuck in the position that you were only getting heat in the front cabin than you could push a straw through the flap openings in the wheel well and you wouldn't have to remove the orange heater hose.

elementsix

Thanks Jason - I think the job for tomorrow will be to look at the red hoses at the rear! Thanks for the tip. Front flaps are definitely in the open position as I manually pulled them open and then attached cable ties to them securing them open - There is absoloutely no hot air coming from the heat exchangers/heater flap boxes - I removed the trim panel where the base of the seat-belt is secured - you can just about get your hand into the gap that leads to the heater-pipe running along the chanel of the floor to the front of the car - this area should be hot - its not.......might be some critters hibernating in there - i know the car was standing for a while and it mice season now!

If you could send me those photos you're talking about I'd be really grateful.

Thanks again, i really appreciate the help

Shane
91 C2 Cab

JasonAndreas

Left heat exchanger outlet


If the flapper valve was stuck opposite to what you have (only hot air in the cabin) than you could push a screwdriver or wrench into the dump valve outlet located in the rear wheel well.



If you remove the orange (originally pink but turns orange) heater hose you'll see the following:


To get heat into the cabin the door needs to look like this,


Use a 7mm socket driver on the hose jubilee clamps as well you'll probably have to 'adjust' the doors by feel. With a mirror you might be able to see into the flapper valves but it is difficult with the transmission in the way.

KirkF

Its nice to have the Bosch Hammer for diagnosing climate control problems. It lets you actuate all the flappers, check sensor inputs, turn fans on and off, etc.

Maybe you can borrow one from someone in your area or local PCA chapter?

Kirk

elementsix

Thanks a million Jason! The picture entitled "To get heat into the cabin the door needs to look like this" - what is the 'gadget inside the heater box?

Shane

elementsix

To one and all who helped, a sincere Thank You. The problem is the heater boxes! I stripped out the passenger side one - bad shape. When the servo(s) in the front packed-up the PO blocked the flaps in the rear heater flap boxes to closed - ie venting into the wheel arches so that the engine would not overheat I imagine. Imaginative but a pain in the ***! Well, at least I know what the problem is now.

Thanks again!

Shane

91 C2 Cab

bmohr

I have exhaust coming into the cabin when the heat is selected. My flapper boxes/vents are functioning the opposite as what is described above. The passenger side with sucking air in, this is where my fumes are coming from. The driver side is frozen i believe. Are these suppose to suck air in? How do I address this? Any advice would be great.

boxsey911

The flapper boxes do not allow air from the outside to be sucked into the cabin. The flaps work so that they allow warm air from the heat exchanger to go to the cabin (when you turn the HVAC control towards the red dot) or they dump the hot air from the heat exchangers out of the wheel arches (when you turn the HVAC control towards the blue dot).

You could draw air into the cabin via the flapper box if the orange connecting pipes are split or a hose clamp has come adrift. I would guess that fumes in the cabin are more likely to be caused by oil getting into a heat exchanger where it will produce oil smoke.

bmohr

My driver side flapper was stuck. Knocked it lose and it's working well know. Even hear the "rattle" when closing the door. I also jumpered the blower relay and now i'm getting use of the front blowers for heat and the fumes are gone. Thanks to the peeps of rennlist again!

alexjc4

Rather than start a new thread i thought that i'd post my q here, for future searchers.

I took one of my flap boxes out today, for non hvac related reasons, it was a bit stiff and was stuck in a half open position. I've given it a clean and a squirt and wiggled it back to life. My question is: how much resistance in the movement of the flap is normal?

frankvan

on mine there is pretty much zero resistance - the flaps move very easily.

alexjc4

ta frank, i suspected as much, i'll keep wiggling maybe soak in penetrating oil over night, see if i can get it freed up a bit more.

jperret

Jason,
First thanks for your great information. I removed my right side flapper valve and it looks OK. However with the flapper out of the car, my heat problem in the sill went away, confirming that the source of the heat is the heater air. Two questions please:
1. Am I correct that the flappers do not have a spring of any kind, and the normal, at rest position is for heater air to flow into the cabin, due to gravity pull on the flapper? When the flow of heater air is blocked into the cabin, the path of least resistance is towards the outside, so as the heated air flow in that direction, pushes on the flapper, which then "flaps", send all the heater air to the outside. When the heater blower is on, the path of least resistance changes to that of the cabin and the valve flaps (quite ingenious actually)?
2. Given a good heater flapper valve, and good internal cabin flex heater tubes, what could cause the flapper valves not to close when the heater is off? My guess is a leak (significant) in the hot air path. Which should be easy to find, but it is not. All I fell is excess heat in the door sill area. - Help Please.

swftiii

Sorry to reserrect this thread, but I have a couple of questions that are related:

1. How much hot air pressure needs to build up in the heat hoses in the sills before the heater box flap opens and dumps the hot air out?
2. Did you ever get an answer on how to address a leak in the door sill hot air path tube (muffler)?

Thanks,

-Skip