Heater Relay.

[chrism964]

The in cabin heater doesn't seem to work properly in my 964, I do not have air con.
Now, I understand that the heater system is not the best design in the world but the fans will only blow air around the cabin if the heater is set below 21 celcius. Otherwise although hot air comes through the vents it is appears only to be passively (i.e. very dependent on the car moving) and thus ineffective but occasionally will blast into life at motorway speeds for about 2 seconds).
On checking the electrics (and replacing some blown fuses which were not blower related (cigar lighter and aerial booster) I noticed that the relay (R14) for the blower was a VAG/Audi part.
Is this a known replacement because it's cheaper than the porsche part or is it a bodge to get the blower working in some form?
Could there be another simple reason for the way the heating system is working (i.e. that is how it is meant to work!)?
Thanks for any help

Chris

 

[Dave Wilkinson]

Chris,

I don't believe your statement regarding "21 degrees" is true. There is no reason for the heater to cut off above that temperature.

R14 in the central electric panel in the luggage compartment is for the condenser fan which is only fitted if you have air conditioning. The relay for the rear blower fan is in the engine compartment panel and is identical to the oil cooler fan relay (R04) which is up front (next to R14).

The most common cause for the rear blower fan to fail is a blown fuse - again, in the rear electrical panel. You don't say what year your 964 is, but if it's an '89 the label inside the electrical panel will say that the blower fuse is rated at 25 Amps. DO NOT replace that fuse with 25A - it was uprated by Porsche in 1990 to a 30A fuse to prevent spurious fuse blowing.

The oil cooler and rear blower relays are identical and can be switched for testing purposes if it helps.

If you turn the temperature dial on the CCU to the red dot the rear fan should start as soon as the ignition is switrched on. If it doesn't come on, check the fuse and relay. The warm air is delivered via the sill trunking under pressure from the rear blower. Only if the temperature sensor in the cabin determines that it is warm enough does the rear fan stop (or slow down). The cabin fans (2 of them) create the pressure to distribute to the windscreen or vents.

Hope that helps.

Regards

Dave

 

[Alan Walker]

Hi,
Just an aside from this heater topic, but referring to relays.......
VW Audi relays are often used as original equipment on Porsches as was the case with my 993. I contacted a VW Audi garage for a spare and was informed that they had none in stock but could order one for me. Price £16 something plus VAT. Tried several other agents, same story / price. Phoned Porsche OPC. They had one in stock at £11 something plus VAT.
Out of curiousity, went onto Maplins Electronics website, and found the same item, but, manufactured to a far higher standard than the Bosch original, and unlike the Bosch, it was hermetically sealed. Actually manufatured by Siemens. Price? £3.40 inc. VAT
Where will you buy your relays in future?
Best regards,
Alan

 

[Guest]

Hi Alan,

I wouldn't mind picking up a spare relay at that price but couldn't find the right one on Maplin's site. Would you mind posting the product code.

Regards

Bob

 

[Alan Walker]

Hi Bob,

I don't know which relay type you wish to have as a spare, but if you do a search on the Maplins site, for "Automotive Relays", you will find their full range.
There has clearly been some repricing since I bought mine, as the prices now vary between £1.79, up to £5.29.

Hope that this is of help.

Best regards,

Alan

 

[chrism964]

Thank you for the replies. I don't think I have expressed myself clearly.
The above 21 degrees relates to the cabin fans. They will only blow when the thermostat dial is set below 21 degrees. Otherwise the only airflow in the cabin I get is passive due to the car's speed of travel.The car does get warm but only slowly.
I will test the blower fan in the engine compartment.