924Board.org

JjyKs · Joined: 05 Oct 2015 Posts: 114 Location: Finland

Hi all,

Winter is slowly coming up, and I've noticed that the heater on my second 924 which i was gonna use in the winter isn't working the same way as on the red car..

It's the 77' model with an "older" control panel with 3 sliders and no knob. Similar to this image:

I have 2 problems.

The first is that the airflow is pathetic at the best (Going to try to plug the fan directly to the battery to see if it's the fan or the control panel, I'm suspecting the control panel since the fan doesn't even start spinning/consuming power before the speed selector is fully opened.

The second and more annoying one is that the car blows warm air only to the windscreen and footwells. The side and center vents blow only cold air. Is this working as intended or is there something wrong? I can't recall how my red 924 worked since I've only used it during the summer and my old W124 mercedes used to blow warm air from side vents to the windows, but cold on the middle.

brian19600 · Joined: 28 Oct 2013 Posts: 375 Location: NJ/CT

Yes that is correct. The dash vents are air only. From what people say, the original fan motor is poor in it's output.
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78 924

prophead · Joined: 12 Jul 2016 Posts: 32 Location: Falkirk, Scotland

I have an '81 model with same heater setup. Recently had the whole dash an heater system out. The fan control is a sliding potentiometer and the tracks can get worn and / or very dirty and need a clean. The fan on mine is quite strong. The side vents are connected to the chamber so should blow warm. A big issue with these systems is the age, many if not all the internal seals will have perished.
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924 GT "8 Ball" track car project
944 Lux rolling project, nearly done

brian19600 · Joined: 28 Oct 2013 Posts: 375 Location: NJ/CT

This thread has more detailed info:

http://www.924board.org/viewtopic.php?p=167314&sid=f7d57d5f151460d9d44adff0adf87a50

I understand that they improved the system in later years so it wasn't as dismal. It has a nice sized heater core. That isn't the problem.

The motor on mine was burned out(along with much of the wiring) and because it has factory air, the motor is different. The only one I could find was over $200 so I improvised a large "muffin" type fan. The output seems pretty good, but I haven't had it on the road yet for real testing.

On the early (77-78?) cars with factory air, one motor does it all. You will get a/c out of the dash vents, but with the a/c on, no fresh air because a flapper closes. My system isn't charged yet so I can't give any opinions on it. I'm not expecting much based on what others say.

Like prophead states, a sealed up heater box is very important if you want any airflow. You also want to close the dash vents when using heat/defrost as you are bleeding off much needed air flow. The dash vents are upstream of the heater core.
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78 924

Noahs944 · Posted: Mon Sep 12, 2016 4:44 am Post subject:

As an interm fix, I directly plugged the ground & power into the "OUT". Meaning power and maybe ground (I forget) that normally feeds the potentiometer and then the result of the sliding variable feeds the heater the power... I unplugged those and went directly to the heater. This means when the fan is on full blast when I have the key on.

Noahs944 · Posted: Mon Sep 12, 2016 4:50 am Post subject:

Extending the 5 fins by about 25%. Riveted & glued on with a strong bonding agent "home construction glue". This modification HELPS if you are careful and match the sizes & weights of your fin additions. I can provide measurements if you like. No other mods were required to fit the fins. There is no perceivable imbalance as a result.

This is by far the worst heater I've had the pleasure of working on