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924 vs 944 HVAC controls
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MikeDanger  



Joined: 21 Nov 2002
Posts: 541
Location: Denver

PostPosted: Thu Nov 06, 2014 5:38 pm    Post subject: 924 vs 944 HVAC controls Reply with quote

What are the differences between the 2? also
on the early 944 I see a rotary switch which I thought was the fan speed setting but then I see some that have both that AND the fan speed selector beween the 2 gauges like this one:


Can the 944 control be retro fitted? Id like to get rid of the big Fanspeed knob.

also is the 944 system lighter than the late 931?
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kcoyle  



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PostPosted: Fri Nov 07, 2014 5:59 am    Post subject: Reply with quote

I believe the late 924's like mine (82 and up I think) have the early 944 HVAC which is pictured. They are split systems so the big A/C knob controls temp and fan speed for A/C and the little one controls heat fan speed.
Early 924 HVAC is a different animal. I think the non A/C cars had a volt gauge in place of the big A/C knob.
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v8carreragts  



Joined: 05 Sep 2003
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Location: Tucson, AZ

PostPosted: Sat Nov 08, 2014 2:21 am    Post subject: Reply with quote

The one in the picture was used starting in 1979. It used a nippondenso A/C unit that was hung under the passenger side dash. Up to 1978 a system put together by Porsche was used where they mounted an evaporator under the dash up against the under side of the battery box. There was a hole cut through the riser between the battery box and the ventilation air intake and there was a cover that fit over the ventilation intake (where the fan is) that covered the hole in the riser. This cover had two doors that were operated by a vacuum pot. When you turned on the A/C these doors would change positions and open the hole in the riser and close the hole allowing fresh air. This allowed the heater fan to suck air from the evaporator that is under the dash. in.

The switch for this had a temperature control switch with a cap tube that was pushed into the evaporator along with a vacuum switch and fan switch. The vacuum switch operated the vacuum pot that mover the intake air doors.

The 79-85.5 control has a fan switch that controls the fan on the A/C unit and a vacuum solenoid that closes two flaps that block off the heater from the dash vent ports. It also has a POT type control to adjust the temperature of the A/C by changing when the compressor turns on and off using a small electronic control box on the A/C unit.

These A/C controls are not interchangeable. The early switch is NLA and used replacements are usually very pricey. Usually what happens to this is the cap tube breaks and the temp control part no longer works. Sometimes the vacuum portion will leak as well.

The 79 - 85.5 system was the same including the early version 944.

As far as I know there was also at least 2 different aftermarket A/C systems available as well that used a separate control that mounted under the dash.
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MikeDanger  



Joined: 21 Nov 2002
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PostPosted: Sat Nov 08, 2014 7:07 am    Post subject: Reply with quote

my 81 doesnt have the lower rotary switch like the one pictured. Just the big knob up top.
I am not going to have ac. so Id like to relocate the switch and Since I don't need the AC control, I just need the Fan speep knob. However id like to be able to shut off the fan completely. I hate the the fact that it runs all the time. Which really sucks when its really cold.
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v8carreragts  



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PostPosted: Mon Nov 10, 2014 4:31 am    Post subject: Reply with quote

The one pictured began in late 82.

The blower runs all of the time and was what they called "flow through ventilation" and was a requirement on all cars in the US. For your 81 you should have the upper switch pictured that is between the oil pressure gauge and the clock. This controls the blower in the A/C unit under the dash and shouldn't run when the A/C is off.

The heater blower in in the slider an the heater control.

The late control like is pictured is the same as the early 944. The system is a little heavier due to the bigger blower. I retrofitted a 79 with the late heater because the blower is much better. However it is a big job because the cutout under the hood (where the blower sits at the base of the windshield) is in a slightly different location. So you need to modify the hole.

I think when the requirement for flow through ventilation began they eliminated the flap that closed off the air intake. The earlier card you could turn the fan completely off and this would close this flap.
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MikeDanger  



Joined: 21 Nov 2002
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PostPosted: Tue Nov 11, 2014 7:14 pm    Post subject: Reply with quote

Ok so can I toss the junk under the battery area. and why couldnt you uses the later controls, if I just want heat, and vent/fan control?
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v8carreragts  



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PostPosted: Wed Nov 12, 2014 5:59 am    Post subject: Reply with quote

You're heater should be controlled by the upper slider for the heating control. All you should need to do is remove the A/C control. The heater blower switch is part of the slider. The A/C control is just an add on.
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MikeDanger  



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PostPosted: Wed Nov 12, 2014 8:44 am    Post subject: Reply with quote

?? The fan is controlled by the knob up top. thats my first concern.
and Id like to move or delete it since there wont be a spot for it with my custom dash. (not to mention it looks terrible) which is why id prefer to put the one with the small knob on the side, like in the picture
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v8carreragts  



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PostPosted: Wed Nov 12, 2014 9:34 am    Post subject: Reply with quote

The 79-82 the A/C knob (big knob on the top) only controls the A/C fan that in in the A/C unit under the dash.

The picture you posted is for 1982-1984 924 and 1983-1985.5 944. However, it uses the same A/C system as the 79-84 924. These have 2 fans, one in the heater and one in the A/C unit.

The heater fan is controlled by the top of the 3 sliders in the heater control. The top one controls the fan and the flap outside; the middle one controls the temp and the lower controls the flap for defrost and the floor outlets.

Could it be that your heater fan does not work and you are getting air through the A/C unit?

For the 81 it is relatively easy to remove the A/C. You basically remove the large round A/C knob and remove the A/C unit from under the dash (passenger side) There are a couple of parts for the center dash vent plumbing that would need to be replaced with non-A/C parts or you would need to plug the opening where the A/C blows in.
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MikeDanger  



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PostPosted: Wed Nov 12, 2014 9:37 am    Post subject: Reply with quote

well yes, I get NO heat right now, and the sliders dont seem to change much, however one of them does change the air flow from center vents to the defrost.
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v8carreragts  



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PostPosted: Wed Nov 12, 2014 11:43 am    Post subject: Reply with quote

Here is the page from an 81 924 Carrera GT manual explaining how the heater works. Maybe your blower fan isn't working, or the switch in the slider isn't working. If I remember correctly, you only get cold air from the dash vents. You only get heat from the floor or the defrosters. This was one reason I updated my last 924 to the late type heater. Also, the late type had a squirrel cage blower and it moves a lot more air.

Sometimes the heater valve breaks and the valve will not open. Or the cable may not be attached. Without this open the heater core will not get hot. The early type blower fan also fails often. You should be able to hear it run and you can see it from the outside if you remove the cover.


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MikeDanger  



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PostPosted: Wed Nov 12, 2014 12:05 pm    Post subject: Reply with quote

well the center upper knob on mine controls A fan and the fan sounds like its in the middle of the dash.
and this fan constantly runs
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MikeDanger  



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PostPosted: Wed Nov 12, 2014 12:06 pm    Post subject: Reply with quote

when you say you updated to the later style you mean the one in the 85.5+??
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v8carreragts  



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PostPosted: Thu Nov 13, 2014 12:10 am    Post subject: Reply with quote

No, the82-85.5 system. It is very close in overall design but you get heat through the dash vents and a much better blower. (moves a lot more air)
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MikeDanger  



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PostPosted: Sat Nov 15, 2014 8:58 am    Post subject: Reply with quote

well since im putting in a custom dash, how tough would it be to put in a late 85+ system?
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