[MCL968]

Whenever they feel like it, the dash vents blow hot air. The air will go from ambient temp to full hot, then eventually back to ambient. The vacuum lines under the hood are intact, the valve holds vacuum so the diaphragm is solid, and the temp control is set to the coldest temp. This happens when I am cruising under moderate power.


I know this is an election year, and we have 11 more months of random hot air, but I think of my 968 as a place of escape from those banalities. This is no longer the case, and I would really like to remedy this situation.


Anyone else out there ever have this problem?


Thanks,


Matt

 

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[ds968]

Yup, once in a while ( though very rarely ..) that also happens in my 968.  If it's of any comfort, it also happens in my MBZ , just as rarely but still... must be a German thing !      

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[Bulti]

Could it be the cabin temp sensor is acting up?

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[ds968]

I vaguely remember a post on some other thread a while back which suggested ALL German cars will default to the heater activating anytime there is some irregularity with the ventilation system.

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[Waylander]

the in car temp sensor fan is full of dust and crap?

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[ds968]

" In car temp sensor " ??? Is there such a thing ? Where is it ?

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[MCL968]

There's a fan in the temp sensor next to the cigarette lighter? I will check that out.

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[az968]

Dan, the cabin temp sensor is the little round grill next to the accessory power supply (aka cigarette lighter). PET doesn't indicate a fan in the temperature sensor.

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[ds968]

Ok thanks guys, I'll have that checked also

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[PorscheG96]

If you follow the hcv vacuum line all the way back under the intake to the rear, there should be a check valve somewhere that prevents the heater vac from going flat during open throttle causing the heater circuit to momentarily open. I have a 968 top end apart and will try to get a pic...

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[wildcat]

Good point, might very well be that check valve, the little blue and black plastic one.

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[MCL968]

I located the check valve, it was right where I replaced the short section of tubing. Any advice on how to test it?

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[wildcat]

If you think that might be the problem, I'd just replace it.  You'd have to know the vacuum that trips it and whether it prematurely opens as a result of hard acceleration or something else like temperature.  As the problem you describe is intermittent that's what I'd do. 

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[wildcat]

As an aside to this, there's a little black cylinder under the fascia above the firewall near the battery.  This is a reserve air pressure canister that provides back pressure for the check valve (to keep it closed, unless the vacuum lines of the heater bypass it. There are two vacuum lines for the heater at the firewall, one orange and one green. ) Its a strange system. You might want to check the vacuum fitting there also. I'm giving you what I've deduced from the evidence. One bolt holds the canister in place. 

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[alausch]

I'm having the exact same problem. Did you ever figure it out? Did you happen to change the interior temp sensor, or the mixer door solenoid by any chance? I'm at a loss here. My heat comes on intermittently as well. Mixer door clip is intact as per "Clarks Garage." Posting a new forum, for maximum views.

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