'86 backdated heat, now heat kinda works

[audi]

Earlier this summer while the motor was out, I backdated the heat plumbing in my 86 coupe.

I should say I'm not super well-versed on 911 heat from the get-go; also, I don't have the levers between the seats, I have the round dial knob behind the e-brake handle.

Before backdating the heat, I could pretty much get the heat to do what I needed it to do, but now when I turn the knob between the seats, usually to about 8, I get heat for maybe 10-15 minutes and then the temperature tapers off gradually and I get just ambient air...not good when you get stuck in pouring rain and the windshield starts to fog (like last week).

Any ideas?

[gsxrken]

Two easy things to check- is your interior sampling sensor/ fan hooked up under the dash? There is a round little grille to the right of the steering wheel that tests the air temp and communicates with the auto heat.
The other thing to check is whether the heat probe is still pierced into the heater hose under the car near the heat flapper box. Also some type of communication to the auto heat...
While you're under there, confirm that the auto heat does pull both cables and both flappers operate. They get gnarly and seize up over time.

[will hung]

Yeah, you shouldn't have problems due to the backdate. As gsxrken said, read up on autoheat, and make sure that it is working properly.

My car has manual handles, and with my original heat exchangers, I had no issues with heat. The only improvement "modern" heat provided over "backdated" heat is that the blower motor provided a steady flow of air through the heat exchangers. Backdated heat relies on the cooling fan, therefore it is dependent on engine speed. As a result, the heat at idle isn't as intense as it is when the engine is revving at 5k rpm. But, as I said earlier, I never had issues with the windshield getting too foggy with my original heat exchangers and backdated heat, so your problem is most likely with your auto heat.

[Rot 911]

What happens when you set the dial over to the max (defrost) setting? That is an override and the blowers should stay on constantly.

[audi]

Thanks for the replies; I'll check out the items mentioned, and should get the car up in the air in the next few days.

Earlier today, per Rot's suggestion, I tried the max (defrost) setting and got, well, nothing.

Guess it's the auto heat somehow...

Must be coincidence, as things seemed to work before the backdate.

[tcar]

Originally Posted by Rot 911

What happens when you set the dial over to the max (defrost) setting? That is an override and the blowers should stay on constantly.

When you 'backdate', the only heater fan you have is the engine cooling fan... no electric fan in the circuit.

Do you get more heat when you rev the motor?

[john walker's workshop]

the footwell blowers will not work if the engine blower motor is dead or out of the system.....unless you take the relay cover off and solder in a jumper to bypass the reed switch.

[wildcat077]

Originally Posted by john walker's workshop

the footwell blowers will not work if the engine blower motor is dead or out of the system.....unless you take the relay cover off and solder in a jumper to bypass the reed switch.

John,

Do you have any details regarding bypassing the reed switch for the footwell blowers ?
It's starting to get colder up here and i do enjoy having warm feet

Cheers !
Phil

[m110]

I don't have time to check now but one of these threads has the details about the relay jumping you need (I saved them for when I got around to it):

Carrera - Removing Engine Compartment Heater Blower

Why you should backdate your heat on a 3.2

Carrera replacement heater blower (long)

Help! Does anyone understand the footwell blower circuit?

heater blower delete in 3.2

[wildcat077]

Thank you for taking the time to post the links,i will definitely give the relay mod a try !

Cheers !
Phil

[john walker's workshop]

pictures on the 1st page.

Carrera - Removing Engine Compartment Heater Blower

[Rot 911]

Yes you need to do the jumper as has been pointed out. This is only for the Carrera. SC doesn't have the footwell blower motors.