carl888 Posted 11July, 2021 Report Share Posted 11July, 2021 After turning the heater on, the heater flaps open as they should and the fan runs as per the manual (As do the fans with the supplementary heater fan rotary switch on the dash) and for the next 90 seconds after start up hot air is delivered as normal. Problem is, after this 90 second period the fans shut down. Turning the heater control does nothing to summon the fans into action, nor does rotating the additional fan switch. I can hear the stepper motor moving the flaps. I've tested the heater control unit, fans, switches, fusebox, interior and exterior temperature sensor, loom continuity and switchgear and have come up empty handed. (Note: the 930 heater set up is different to the 911 Carrera, there is no engine bay heater relay nor an engine bay heater fan) The additional fan relay (position 4 in the fusebox tests fine). Any ideas? Quote Link to comment Share on other sites More sharing options...
sus911 Posted 11July, 2021 Report Share Posted 11July, 2021 Man the mystery of air-cooled heater system diagnosis. Good luck with your fault finding but alas I have nothing to offer! I see that you also have (or had) a 3.2? I don't suppose you have any knowledge of backdating the heat on these? I have an '84 that I backdated the heat on using 993 Bischoff HE's & the usual engine compartment fan delete. I did the suggested relay terminal jumper solder job and confirmed the footwell blowers are functional but can't get the system to operate them. I have heat with the autoheat servos & flapper boxes working as they should but no fan forced air via the footwell blowers. I did read somewhere that it could be an issue with the thermistor or thermostat but stuck at this point. Sorry to hijack...... Quote Link to comment Share on other sites More sharing options...
WB997.2GTS Posted 11July, 2021 Report Share Posted 11July, 2021 Hi there, You could look up this Bergvill FX site, Tore explains the operation and testing procedure for the ventilation controls. https://www.bergvillfx.no/en/categories/diy-section Quote Link to comment Share on other sites More sharing options...
sus911 Posted 11July, 2021 Report Share Posted 11July, 2021 8 minutes ago, WB997.2GTS said: Hi there, You could look up this Bergvill FX site, Tore explains the operation and testing procedure for the ventilation controls. https://www.bergvillfx.no/en/categories/diy-section Looks like 964/993 only. Quote Link to comment Share on other sites More sharing options...
carl888 Posted 12July, 2021 Author Report Share Posted 12July, 2021 3 hours ago, WB997.2GTS said: Hi there, You could look up this Bergvill FX site, Tore explains the operation and testing procedure for the ventilation controls. https://www.bergvillfx.no/en/categories/diy-section Thanks for the link, there's quite some information there however it's not relevant to my car (1985 930, completely different system) 4 hours ago, sus911 said: Man the mystery of air-cooled heater system diagnosis. Good luck with your fault finding but alas I have nothing to offer! I see that you also have (or had) a 3.2? I don't suppose you have any knowledge of backdating the heat on these? I have an '84 that I backdated the heat on using 993 Bischoff HE's & the usual engine compartment fan delete. I did the suggested relay terminal jumper solder job and confirmed the footwell blowers are functional but can't get the system to operate them. I have heat with the autoheat servos & flapper boxes working as they should but no fan forced air via the footwell blowers. I did read somewhere that it could be an issue with the thermistor or thermostat but stuck at this point. Sorry to hijack...... No problem, I still have the 3.2 and the system in that car is faultless. OK, so we sort of have the same problem. My next step is to measure the voltage on the loom from the fusebox and at the fans. I am very suspicious as to why mine runs for 90 seconds every morning however, then shuts down. I'd be happier if it never worked at all! The relay, switches in the heater control unit or a bad earth somewhere seem to be the only possible issues. Not sure how the thermistor or thermostat could be the issue in your case if the rest of the system is functional. Question, what are you using as a fan switch, the integral switches with the original controller between the seats or did your backdate consist of dumping the original heater control unit and installing the earlier style levers with the integral switches? Some specifications and diagrams of the 930 system: Quote Link to comment Share on other sites More sharing options...
sus911 Posted 12July, 2021 Report Share Posted 12July, 2021 I retained the autoheat in between the seats and this controls the servo for the flapper boxes as it should. The problem is deleting the engine compartment blower and modifying the HVAC relay on the LHS of the engine bay to run the footwell blowers in the absence of the rear blower fan. Quote Link to comment Share on other sites More sharing options...
carl888 Posted 14July, 2021 Author Report Share Posted 14July, 2021 On 13/07/2021 at 08:00, sus911 said: I retained the autoheat in between the seats and this controls the servo for the flapper boxes as it should. The problem is deleting the engine compartment blower and modifying the HVAC relay on the LHS of the engine bay to run the footwell blowers in the absence of the rear blower fan. OK, Lake Cathie, what a beautiful area, lucky you. I would start with the relay. Have a poke around with a voltmeter to make sure 12V is getting to the fans. Perhaps do a continuity test from the fans to the relay first. Quote Link to comment Share on other sites More sharing options...
sus911 Posted 17July, 2021 Report Share Posted 17July, 2021 Will do Carl. Electrics not my forte but capable of following instructions! Quote Link to comment Share on other sites More sharing options...
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