Heating system troubleshooting for 911SC 82?

[francesconyc]

I recently brought my '82 SC to my mechanic and they replaced the 2 heater control valve boxes and the main cable to open/close them with the lever i have between seats. (FYI i have those fancy auto-heat box between the seats with 1 automatic lever and the rotary switch form 0 to DEFROST)

Despite last year i replaced the electric blower on the back but I still cant feel the hot air blowing in my face.

The system never worked when i bought the car so i don't know what to expect, ...AM I supposed to feel a strong air in my face at all??
When i put my heating to max DEF what i'm supposed to feel and from where?

the heat seems to come inside the cabin only when i drive faster than 30mph ro so but when in traffic the air doesn't come through and is pretty chill in the car.


my next troubleshooting steps:


1. check if the boxes below the car actually open and close when the level is pulled/pushed
2. check if the rear blower actually starts/stop
3. check if all the wiring is ok and the blower works properly
4. check if i have any dispersion, missing worm clamps between the hoses


anything else I should do after this? blockages maybe?
thanks

[proporsche]

did you do back date on the heating at the engine? Do you still have the el. heater motor there? If yes -it is most likely not working..is this the 4th problem you have from the same people -mechanic???

Ivan

[JSV798]

On my 1978SC, with the ignition on (no need to start engine) when the rotary switch is turned the fan in the engine compartment comes on and the mechanism in the heater box between the seats moves the lever to open the heater boxes. Are you getting any of this?

Roy

[EC900]

https://members.rennlist.com/imcarthur/ahoverview.htm

[Alan L]

Yes, verify the fan in the engine bay is working with key on and heat dialled in on the rotary knob. I don't think you need the engine running - as stated above, but run the engine if no heater action - just to check. It should be obvious if it is going. If it is working, then look under the car and see if the flaps are closing in response to how much heat you dial in - go to full setting and they should be fully closed or near to.
I recently had to rebuild my SC heating - control rod in the auto heat box was failing and the control wires to the flaps needed replacing. And I replaced the air blower some time previous.
Check what is working - or not. You should be able to cook an egg inside the cabin when on full blast. There is also the temp sensor in the roof - by the rear view mirror. If things are not working, you may want to pull that and check it is connected. Can't remember exactly how it fits in to the wiring scheme - but it is part of the loop.
Alan

[Flat6pac]

The box between the seats, right side access there is a pull rod with nylon snaps each end.
40 years later, the nylon breaks and the wires to the control boxes have dirt in the tubing. Tubes. Are inexpensive to replace.
Bruce

[francesconyc]

Ok i finally had time yesterday to check everything
- rear blower works when battery is on.
- blower is Noisy but it spins in the right direction (from the alternator fan to the bifurcation ducts. - - i removed one of the hoses and if i put my hand on the exit hose is not a blast but more of a gentle whiff … is this normal? The blower is brand new. Is it supposed to be like that?
- i checked the valves under the car and they seem to be closing properly. To be pedantic i think they are not well fine tuned by my mecanic and i can see a little 5% open but in theory it shouldn’t be a problem.
- if i drive fast i can feel a bit of the heat coming in from the tiny side vents and windshield vents
- but overall when i put the heat to max level 9 - DEF and thr level all the way to max def i dont feel a blast at all…

What else can be possible to check?? Is it possible that i have clogged ducts somewhere?

[francesconyc]

Originally Posted by Alan L

Yes, verify the fan in the engine bay is working with key on and heat dialled in on the rotary knob. I don't think you need the engine running - as stated above, but run the engine if no heater action - just to check. It should be obvious if it is going. If it is working, then look under the car and see if the flaps are closing in response to how much heat you dial in - go to full setting and they should be fully closed or near to.
I recently had to rebuild my SC heating - control rod in the auto heat box was failing and the control wires to the flaps needed replacing. And I replaced the air blower some time previous.
Check what is working - or not. You should be able to cook an egg inside the cabin when on full blast. There is also the temp sensor in the roof - by the rear view mirror. If things are not working, you may want to pull that and check it is connected. Can't remember exactly how it fits in to the wiring scheme - but it is part of the loop.
Alan

I wish i could buy you a beer but if you have time could you take a video of you switching on you heating at idle or slow run?
My main problem is that I am cold when im stuck in traffic and i have zero blast from my vents
Thanks!!!

[francesconyc]

The only thing i have no idea if it’s working os the sensor on the roof but i guess i dont care because i dont need automatic features i just need heat mainly when my windshields get foggy

[francesconyc]

last quick thought. Is it possible that my rear blower fan has the polarity invested?
It feels strange to me that it pushes just so little air. I wonder if it is spinning in the wrong direction.
Unfortunately, I have no reference for how it should work I cannot find videos on YouTube about it.

is it supposed to blow air as powerful as my fresh air blower? if so then something is wrong with mine.


if you have any video of how it should work that would be amazing. because it drives me nuts this problem that seems so simple.

[wazzz]

You mentioned the blower is new. Is it OEM or aftermarket? Anyway, connection is normally fool-proofed, so no real reason it should turn in the opposite direction. Or did the mechanic have to adapt the connector to the car? If so he could have done it wrong.

[mysocal911]

Originally Posted by francesconyc

The only thing i have no idea if it’s working os the sensor on the roof but i guess i dont care because i dont need automatic features i just need heat mainly when my windshields get foggy

Then the system thinks it's very cold, and the rear heating flaps are always fully open at max heat.

[mysocal911]

Originally Posted by francesconyc

last quick thought. Is it possible that my rear blower fan has the polarity invested?
It feels strange to me that it pushes just so little air. I wonder if it is spinning in the wrong direction.
Unfortunately, I have no reference for how it should work I cannot find videos on YouTube about it.

is it supposed to blow air as powerful as my fresh air blower? if so then something is wrong with mine.


if you have any video of how it should work that would be amazing. because it drives me nuts this problem that seems so simple.

Obviously not, since it's in the rear, a "long distance" for air travel, right?

[Alan L]

If the fan plug is original, it cannot be inverted - it is 'idiot proof'.
My after market fan had the proper connection to plug in to the harness.
I get a fair rate of hot air migrating in to the cabin once the system is On. I usually have to dial it back to around 3 to be tolerable. beyond that you start shedding clothes.
Having said that I seem to recall the flow thru the screen vents is not high. It is discernable but not a gale force blow.
Alan

[Alan L]

One thing you could check is with the heat on DEF, see how much air you are loosing at the heater controlled flaps under the car. Slide your hand underneath. If they are not fully closed, then you will be loosing air thru the gap. Does it feel like a significant amount compared to the flow at the fan?
I will check and try and get an estimate of how much my fan is shifting.
Alan

[Alan L]

I disconnected the smaller of the two Y hoses exiting the fan in the engine bay. I get a steady strong breeze of air. Bear in mind the bulk of the air is probably going down the larger of the two hoses.
it is not gale force but a discernable push of air.
The fan only goes at one speed. It is either working, or not.
If you aren't getting much flow in the cabin, or the vents, you could be loosing air at the flap valves, or maybe some hose is disconnected further along the system, or one of the boxes behind the dash (in the frunk) have come open or disconnected.
Alan

[smadsen]

On my '82 I replaced all the tubing, verified the blower worked, replaced the flapper box cables and lubed, adjusted and tested the flappers, then I went out on a cold morning and.....nothing.

I discovered it takes a while for the exhaust pipes to generate enough heat in the heater boxes, heat soak the parts & tubing and then blow into the cabin down AT YOUR FEET. On a cold morning it can take 3-5 minutes (depending on if you climb a steep hill to build heat), and then the cabin suddenly becomes insufferably hot. Then you have to open a window or sunroof, or learn how to trim the flappers to maintain equilibrium.

[porschedude996]

Originally Posted by francesconyc

Ok i finally had time yesterday to check everything
- rear blower works when battery is on.
- blower is Noisy but it spins in the right direction (from the alternator fan to the bifurcation ducts. - - i removed one of the hoses and if i put my hand on the exit hose is not a blast but more of a gentle whiff … is this normal? The blower is brand new. Is it supposed to be like that?
- i checked the valves under the car and they seem to be closing properly. To be pedantic i think they are not well fine tuned by my mecanic and i can see a little 5% open but in theory it shouldn’t be a problem.
- if i drive fast i can feel a bit of the heat coming in from the tiny side vents and windshield vents
- but overall when i put the heat to max level 9 - DEF and thr level all the way to max def i dont feel a blast at all…

What else can be possible to check?? Is it possible that i have clogged ducts somewhere?

My bet is the blower motor is worn out. See if the fan wobbles. Of course when it’s not powered up. My airflow (1983 SC) from the engine cooling fan/alternator is huge, which is the supply to the auxiliary fan. Should be able to blow the leaves off the lawn.

With the engine idling, the aux fan running, and the air control boxes under the car open, triangle windows open, you should have a lot of air coming out of the little windows. You might peel back the carpet below the “A” pillar and see if you have air flow with the duct disconnected from the body. I have never heard of the ducts being plugged, but who knows what can happen over the decades.