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Good A/C - No Heat

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Old 09-13-2007, 10:40 PM
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mlister
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Default Good A/C - No Heat

I'm the proud new owner of a 1983 928S. All and all, the car is very solid. I bought it in Phoenix, flew out and drove it straight back to Denver without a problem. In the process of going through the car fixing all the little problems, I've run into one I need advice on:

I can get the blower to work (all speeds) but A/C is either full cold or off. No heat whatsoever with the controls in any position.

Can somebody point me in the right direction? I'm supposed to have a shop manual on CD coming but it won't be here 'til next week.

Thanks! Mark
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Old 09-14-2007, 01:02 AM
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leperboy
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Originally Posted by mlister
Can somebody point me in the right direction? I'm supposed to have a shop manual on CD coming but it won't be here 'til next week.
Mark, welcome. There are quite a few active 928 owners in the Denver area and we have quite a few get-togethers to occasionally work on cars and frequently drink beer and eat food. Send me a PM and I will give you info about getting on the mailing list if you''re interested.

As for your no heat issue, there are better experts on here, but you may want to check your heat exchange valve and see if it is stuck shut.

Matt
Old 09-14-2007, 01:33 AM
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Bill Ball
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Most likely you car's PO in Phoenix wired the heater control valve shut. Not much need for it in that area. Also, this usually indicates that there was a problem with the valve and the owner felt the need to disable it.

Pull the air filter box off. The valve is under it on the passenger side. The stock valve is black and cream plastic with a short hose that attaches it to the block and a long hose going via the windshield cowl to the heater core. It should have a vacuum line going to it as well. If you find its actuator arm wired shut and cut the wire, you may find you have heat all the time now or a reduction in the effectiveness of the AC due to heat leakage. This means either the valve leaks internally or it is not getting vacuum or responding to it. Without vacuum, the valve is open.

Anyway, have a look down there and see what you find.

Also, you may have other issues. If after you fix the heater valve, you do not get climate control temperature regulation, but either full AC or heat and nothing in-between, it is likely that either or both the exterior and interior temperature sensors are not working. The exterior temperature sensor in in the driver (left) side front wheel well near the headlight in a 2 1/2" air intake tube that runs from there to the alternator. You have to remove the wheel well liner to get to it. You'll see a metal section in the tube with an electrical connector there. You can test the sensor. I've found the wire connector there to be corroded. The interior sensor in behind that tiny round grill in the dash near the glovebox. It's a PITA to replace, so hope it is OK. Anyway, if you do have lack of climate control, come back and we can go over how you can test both sensors at a connector behind the radio.

Last edited by Bill Ball; 09-14-2007 at 01:33 PM.
Old 09-14-2007, 01:18 PM
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mlister
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Hi Matt, Don't think I can PM yet... but yes, please put me on the list! Frequent eating, drinking and occasional working is good! Thanks for the help.

Mark
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Old 09-14-2007, 01:20 PM
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mlister
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Thanks, Bill. I'll dive in and see what I can find this afternoon. Appreciate the help! Mark
Old 09-14-2007, 08:29 PM
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Alan
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Can you get any heat with the AC off? try all the way hot (listen for the click point) does it go hot then?

This is the "max heating" mode and I believe it overides the "max cooling" mode - if they should ever be on together (not supposed to be possible by the design).

Reason I say this is that its also possible your "max cooling" switch is stuck on.

Max cooling mode turns off the closed loop temp control, closes the hot water valve and fully closes the heater mixer flaps - and it just keeps cooling as much as it can.

Max Heating mode turns off the closed loop temp control, opens the water valve and fully opens the heater mixer flaps and heats as much as it can.

I like Bill's suggestion as a good starting point though - especially if you can never get any heat.

Alan



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