MD355

This is my second 993, so I have an idea of how the heater / blower on the 993 should work.

In my old 993 C2 (1995 model US non-Varioram) when you had the heater speed at 0 , there was no heat or air coming from the vents.

In my "new" 993 C2 (1995 model German non-Varioram) , when the heater speed **** is at 0 , if I increase the temperature **** for heat, it starts blowing hot air, regardless of the selected heater speed.

This is weird, as there seems to be no way to turn off the air !! The only way to decrease almost to zero is if I put a low temperature on the **** and the outside temperature is also low.

Furthermore, I noticed that there is a constant whining noise from the operation of the auxilary blower from the engine bay (as if someone has manual put the secondary blower to always on mode).

I also noticed something strange in the engine bay... Someone seems to have made a fix see picture... Is this some custom automation made to the heater ? I never got a chance to ask previous owner...

ToreB

Check operation of rear fan. At cold engine, it shall not run with fan speed set to 0. It shall run on low speed on fan 1, and full speed on fan speed 2 and above.
You might have a defective rear fan relay, (sticking on low or high) or rear fan resistor. You could also have a defective rear air temp sensor, causing the fan to always run in cooling mode.
See my DIY for details on how to test the rear fan.

The cable adapter on the rear air selector vacuum valve is normal, many 993's have this. I guess they had two types of vacuum valve in stock, and type depends on model year or other production variants.
Cheers,
Tore

pp000830

Is it truly blowing hot air with the assist of the engine compartment heater fan or is it hot air wafting through the system from the air pressure supplied by the engine cooling fan. It may be that the heat servos are not closing when they should. There is a comprehensive diagnostic process document floating around this board I believe originally posted by Tore - BERGVILL.
Andy

Railmaster.

The coupe fan on all but the earliest 993s do blow a little air even when shut off / switch in O.
The thing in the engine compartment picture, isn't that the shut off valve closing when the car is in reverse gear to avoid exhaust fumes from entering the fresh air intake?

pp000830

I read once is that the valve is used to direct air driven by the electric blower in the engine compartment once the engine is off to provide additional engine cooling when the engine's fan is no longer turning.

In the other position the electric blower draws fresh air from the duct opening next to it as a fresh air source to the cabin.

Not perfectly clear on this.

ToreB

Just to clarify the above statements:
All 964 and 1994 993 Climate Control Modules does not allow the two main blowers to be completely shut off. Fan setting 1 and 0 is the same fan speed in these cars. All later 993's allow fan speed zero.

The vacuum actuator in the pic is the rear air selector valve. When reversing, this valve change position in order to avoid exhaust fumes being drawn into the cabin. Cabin air is otherwise drawn from the main engine fan. This selector valve is only activated when heated air is needed to the cabin.

Engine cooling by the rear electric fan is obtained by closing the two mixer valves (when no heat is needed to the cabin) and dumping the heated air out of the rubber valves on the exhaust system.
Cheers,
Tore

nk993

I have a slightly similar issue. When it’s on 0, either at idle or driving around town, it’s definitely off. But once I go over about 60mph/100kmh there’s a lot of air blowing from the vents. Almost as much as when the fan is on 1 or even 2 around town.

is that normal, or is something broken?