heater blower relay on 84 carrera

[Dirkclod]

trying to get fresh air fan and heater fans to work. my ? is i checked the rear fuse panel and this relay is missing. the plug where it goes is there but no relay. would this also mess up fresh air blower ?? talked with host here about part and it"s over 100 bucks and can"t return electical parts. i do not know why relay is missing but i think i need it. anyone got a clue ? thanks

[911mot]

I'm not sure but isn't the relay in the back for the engine blower motor?
Fresh air blower motor is mounted up front and known to fail.

[Dirkclod]

i really don"t know but all my fans don"t work so i seem to think theres something somewhere unhooked or something !!!! a/c fan works but thats it.

[imcarthur]

The fresh air & heated air systems are totally separate.

Fresh Air - Front Blower (in trunk)

Front trunk fuse panel: Fuse 6 panel 1 (Middle) is the fresh air fuse. Check fuse & check power on line side of fuse.

If OK than you have to do some work & disconnect the fan & test with a direct 12V feed.

Heated Air - Main Engine Blower

Rear panel fuse & rear panel relay. If relay is missing, run 12 volt line to fan & check it. You will need the relay. These relays do fail & are not cheap (as you found out). In the image below it is the one on the left. The larger one on the right is rear defogger.



This relay also operates footwell blowers - one per side - which are called aux blowers in Bentley. Run a 12V line & check each.

[Dirkclod]

thanks im, will do this just as soon as this ms sun goes down and it cools some. 110 heat index and no shade tree !!!!!!!

[imcarthur]

Hey what do you need heat for anyway?

The heating/fresh air/ac systems in your car are 3 separate systems. You can have them all running at the same time.

In the pic below, subtract the Automatic Heat Sensor & the Automatic Heat Control & that is what you are dealing with. I left out the AC components, because that becomes too confusing for anybody. There is also a resistor on the Fresh Air Blower - for mutiple speeds - but I'm not sure where.

[indigowhale]

I got the same problem, my heater blowers have just quit working and I also don't hear the automatic control unit motor opening the heat exchangers. All fuses are good and there is voltage.

Hopefully that darn heater relay didn't go out on me!

Where should I look if fuses and relay are OK?

The fresh air blower is toast like many others.

[indigowhale]

OK, found wire for heat control unit disconnected at the luggage compartement fuse box. Now heat exchangers open. No electric fans though.

Opened up heater relay and pressed on solenoid switches inside it. All 3 fans started working (engine and 2 foot wells).

So how do I test this relay further? It shows no signs of burned components and it is getting power in all the terminals that it should, which I think are four. I will post a picture of the innards later.

Anyone got one laying around?

[Mysterytrain]

Dirk- as stated by the others you have two systems here. The fresh air blower lives behind the cardboard panel in the trunk, just behind the dash. Its a bit of a pain to get to but an easy task. You should be prepared for the paper /plastic hoses falling apart once you mess with the system. You are going to need a wiring diagram [bentley would be good enough]so you can figure out which pins on the motor connector are power and ground. There are four pins as I recall. If the fuse tested good then run a jumper up to the blower and see if that is working. If the blower is good then you will have some real fun tracing the the wiring to determine where the fault is. If the blower is bad then you still will have the pleasure of replacing the motor or the complete assembly.
Now, you carrera guys have a more 'advanced' system then us SC'ers especially if you have autoheat. First, you need to ck the rear blower motor to see if its good. These things like to cook themselves to death back there and if the motor is bad it will not allow the footwell blowers to operate! Each of the footwell blowers should also be tested so that you can move on to other issues in the heating system. After you are happy that you have three working blowers or you have unplugged all the bad motors from the circuit you can dig into the rear fan relay [the one that is missing]. It might have been removed for a reason so I would exercise some caution by testing the wiring. When the ignition is in the on/run position and you call for heat by lifting the levers or twisting the knob on the autoheat console 12 volts is sent thru the rear relay to energize it. The relay closes its contacts [like a switch] and sends 12 volts, directly from the battery and the fuse panel in the back to the rear blower motor. This is the basic operation of the system. I would test to see if I had voltage at the relay socket. You need a wiring diagram to do this correctly and/or some patience. Turn the ignition on, turn the heat control to heat and then stick one voltmeter probe in the relay socket and the other to ground. I'm looking at a drawing now for an older car..it appears that fuse S22 directs 12 volts to pin 86 and from there it would go thru the relay coil and out thru pin 85 and from there up to the heater levers or knob in the control panel and then finally to ground. The actual power for the rear fan comes from the battery to fuse S23 and then to pin 30 on the relay. When the relay is energized the 12 volts appears at pin 87 and then goes to the blower. Ok, so with no relay in the socket you should have seen 12 volts at pin 86 and 30 and zero volts at pin 85 and 87. If its different then you need to find out why. If it tests good I would then replace/reinstall the relay. Once you rule out the basic stuff, then you need to look at the Aux blower relays in the front trunk, the inline fuses on each of the aux blowers [ some have, some don't, all should] and then for the auto heat systems the electronics in the heat control unit and the controller in the engine compartment. Damn, I hope this is of some help.

[indigowhale]

Openned up this silly relay, after careful study, found one of the transistors solder had come loose. This explained the intermittent running of the heater fans. Had a technician solder it at work and all is well now. Saved a few hundred dollars as this part is almost 300 at the dealer. Not a good place for electronics mind you in the engine bay. When will they learn....

[POZE]

Hello

Good post- hopefully someone can advise me on a few things relating to the heater blower motors and the relays in the engine compartment.

I own a autoheat 3.2 1985 Carrera , i have the 2 large relay/control boxes in the back, but no small round relay on that same board - is this needed? or what should it be for - its completely missing.

And my main issue - my Control Box is faulty - the front blowers come on but are not operating correctly - the relay inside (small one) 'chatters' loudly (turning on /off quickly), so gives low power to the front blowers. When u adjust the dial it does give more power, but still chatters away.

Any ideas? i have cleaned everything and the joints, but no avail.

Thanks,
Poze UK . Or i 'll just go and buy a new one!

[dshepp806]

EXACTLY! As to the internal solder joints,..I reflowed several points there, as well as DME,...on a UNsympotomatic 89,...heat is the enemy, in this cae. I call it preventive maintenance!!!!! Luckily I "wheel" my soldering techniques as well as I "wheel" my guns and P-driving!!!!!!!!!!

Good work!

Best,

[Mutley23]

im having the same issue with my1984 911 the rear fan works but no power from the cable any ideas