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88 930 heater diagnosis help
Hi all,
My 88 930's heater is acting up. With the ignition on, the foot-well blowers act normally and run at three speeds depending on the position of the heat control. Then, they suddenly stop, and only restart if I turn the heat control back to 2 or less, and turn the controller up again. The fans will increase in speed and stop after a few seconds. They will always restart for a short time if I turn the heat back down to 2. Any ideas before I tear into it?? I am thinking maybe a short or open temperature sensor is killing heat. Does anyone know if this is in fact normal behavior, I was thinking maybe the system would not let the foot well booster fans run until the temperature sensor in the heat ducts from the motor saw some heat, but I'm pretty sure its dead (i.e. no foot well fans running) when I'm driving it also. I plan on testing it in the coming days. Thanks in advance.
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1988 930: 3.5L 100mm LN slipins, LN FFA rods, Supertec studs, GT3582R with T4 1.07A/R twin scroll housing, RarlyL8 equal length divided headers, dual Tial MVS 38mm WG's, Carrera 3.2 heads with 993 big valves. 964 Cams, full bay IC, KEP st1 clutch. PE3 sequential ECU with 750cc EV14 injectors, CoP twin plugs, J&S Safegaurd, Aquamist HSF3 water inj. Wavetrac LSD. |
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10-04-2016, 03:30 AM
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Administrator
Join Date: Aug 2016
Location: Los Angeles, CA
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Hey b930....I've attached a link to a tech article from our site that I think will be very useful for you in troubleshooting and hopefully fixing your heater issue. If you have any further questions, please do not hesitate to post a Comment just below the article and someone will get back to you with more detailed info. Best of luck!
 Porsche 911 Heater System Repair | 911 (1965-89) - 930 Turbo (1975-89) | Pelican Parts DIY Maintenance Article -Dmitry |
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10-04-2016, 03:46 PM
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Fleabit peanut monkey
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Quote:
I am guilty of not referencing them enough to help folks.
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1981 911SC Targa |
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10-04-2016, 03:50 PM
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Thanks for the link Dmitry, does anyone know if the heat exchanger temperature sensor stops the footwell booster fans running unless it senses heat?? (i.e. to prevent blowing cold air?).
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1988 930: 3.5L 100mm LN slipins, LN FFA rods, Supertec studs, GT3582R with T4 1.07A/R twin scroll housing, RarlyL8 equal length divided headers, dual Tial MVS 38mm WG's, Carrera 3.2 heads with 993 big valves. 964 Cams, full bay IC, KEP st1 clutch. PE3 sequential ECU with 750cc EV14 injectors, CoP twin plugs, J&S Safegaurd, Aquamist HSF3 water inj. Wavetrac LSD. |
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10-04-2016, 10:17 PM
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Which type of heat do you have? Do you have the full autoheat where the box between the seats turns to 10 and you have no levers? Or do you have the "not full autoheat" where, if memory serves, you have the two levers still and a knob that turns to 5?
On my '87, I have full autoheat, and replaced the "caloric sensor" in the driver's flapper last season with an equivalent thermister (thanks to this forum). The footwells seem to be hit or miss in terms of how much they run, but frankly I don't know what's considered "correct". I do know that I finally any heat that is variable instead of just off or surface of the sun hot. Matt
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1987 911 Carrera coupe - Guards Red 2010 997.2 C4S 6-Speed 2005 Mini Cooper Convertible (R52) - Wife's car 1977 VW Bay Window Camper Bus |
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10-05-2016, 05:14 AM
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here is the link you need.
check the little fan under the dash that blows air across the temp sensor. (I doubt that's the problem). there is a separate relay for hi speed.
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86 930 94kmiles [_  _] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD88 BMW 325is 200K+ SOLD 03 BMW 330CI 220K:: [_ _] RUNNING: [__] NOT RUNNING:01 suburban 330K:: [_ _] RUNNING: [__] NOT RUNNING:RACE CAR:: sold |
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10-05-2016, 06:28 AM
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Location: Los Angeles, CA
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We're here to help guys. Use the tech articles as often as needed!
-Dmitry |
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10-05-2016, 09:38 AM
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its full auto heat I have. I'll do some digging and see what I find, appreciate the help.
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1988 930: 3.5L 100mm LN slipins, LN FFA rods, Supertec studs, GT3582R with T4 1.07A/R twin scroll housing, RarlyL8 equal length divided headers, dual Tial MVS 38mm WG's, Carrera 3.2 heads with 993 big valves. 964 Cams, full bay IC, KEP st1 clutch. PE3 sequential ECU with 750cc EV14 injectors, CoP twin plugs, J&S Safegaurd, Aquamist HSF3 water inj. Wavetrac LSD. |
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10-05-2016, 05:42 PM
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Join Date: Jun 2011
Location: Hudson, Ohio
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i have auto heat and used a number of the forum articles to get myself up to speed. It ended up being a slow process of elimination. I bought a used center console, ended up replacing the thermister in the heat exchanger (big pain), the thermister in the cabin sensor with the little air circulating motor (easier) and finally got it to work. It's really a true marvel of late 80s electronic wonkiness! I've seen quite a few backdate to VW Buglike setup which works.
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Northeast Ohio 1987 Porsche 911 Targa 1966 VW Beetle, 6V |
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10-05-2016, 06:10 PM
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Glad it worked out!
My first observation is that the thermistor in the heat exchanger is open circuit. The cabin one looks good at around 2kohm ~18C. I am hoping to splice in an equivalent thermistor and will hopefully see it working better. We'll see.
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1988 930: 3.5L 100mm LN slipins, LN FFA rods, Supertec studs, GT3582R with T4 1.07A/R twin scroll housing, RarlyL8 equal length divided headers, dual Tial MVS 38mm WG's, Carrera 3.2 heads with 993 big valves. 964 Cams, full bay IC, KEP st1 clutch. PE3 sequential ECU with 750cc EV14 injectors, CoP twin plugs, J&S Safegaurd, Aquamist HSF3 water inj. Wavetrac LSD. |
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10-06-2016, 03:07 AM
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Location: Hudson, Ohio
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Good luck and let us know how you make out. It takes some persistence!
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Northeast Ohio 1987 Porsche 911 Targa 1966 VW Beetle, 6V |
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10-06-2016, 04:37 AM
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I've installed a locally sourced roughly equivalent NTC thermistor by drilling out the old component and sealing in the new one with HT RTV. One thing I need to check is the resistors for the footwell fans that give the three speeds, does anyone know where they are located on an 88 930?
TIA |
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10-07-2016, 03:57 PM
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1981 Porsche 911 SC Targa
1987 Porsche 911 Carrera
