Randall G.

[quote]Originally posted by Randall G.:
<strong>***snip***

Furthermore, I don't know what the setpoint (rear blower temp. sensor) is for starting the blower (I don't think anyone does ).</strong><hr></blockquote>

Damn, leave it to Robin to know the start/stop setpoint for the rear-blower engine cooling function.

Good work, Robin. <img src="graemlins/r.gif" border="0" alt="[king]" />

Tom T.

[quote]Originally posted by Hank Cohn:
<strong>Buck:

When my wiring harness went bad, my engine fan would run continuously.
&lt;snip&gt;
Hank</strong><hr></blockquote>

Hank & All,

Back in 1999 when I was buying my 1995 993, the technician who did my PPI found the engine
blower motor connectors separated. When he
connected them the fan would run continuously.
As part of the deal he was to fix it. After he fixed it the fan would run from time to time after shutting the engine off. This is normal to vent off heat. However now I have noticed it only running when I turn the ignition key to the "On" position, and in addition
even when the engine is cold. Now I am also wondering if my engine harness is bad considering Hank's symptoms are the same as mine. When I checked my harness p/n last year it seemed to be the updated one.

Since my fan does work, my guess (or hope) is either the relay or the temp-sensor are bad. I still plan to test it the fan out as Randall suggests to be thorough. My question is how can I test the temp-sensor and relay with a DMM? Is there a part number on the temp-sensor or another way to easily identify it?

Tom

Robin 993DX

Tom,

There were additional information I left out about the engine aux. fan in my priviouse post, because I was only answering Buck's questions, which were the fan noise when the engine is off.

The engine aux. fan is also programmed to turn on under different parameters when the key is on.

The power to the engine aux. fan when the key is on is determined by the settings of the temperature mixing flaps, (your temperature control ****), but if the temperature is turned up than the fan speed control **** takes over priority control.

According to the shop manual, it was referring to blower potentiometer, which I believe to believe the fan control ****.

It also said that the 1st stage is - 0.3 to and less than 2
2ns stage is 2.0 to 4

But also keep in mind that if the temperature control **** is turned all the way off (to the cold), the temperature mixing flap which is closed at this time and the engine aux. fan is only controlled in accordance with the air temperature by the temperature sensor at the engine heater air intake duct area.

1st stage on at 45 degree celcius
off at 40 degree celcius

2nd stage on at 62 degree celcius
off at 57 degree celcius

So that which may explain why your engine aux. fan is running when you turn the key on.

tom_993

[quote]Originally posted by Robin 993 DX In Atlanta:
<strong>In your case with the engine off the aux. fan was preprogrammed to turn on at 75 degree Celcius, and off at 70 degree Celcius. The temperature is determined by the temperature sensor located at the heater duct intake area ont he left side of the engine.</strong><hr></blockquote>

I think this is the cause of the fan cycling on and off (with engine off). The air quickly cools the surfaces and temperature sensor to below 70C. After a few minutes, heat flows back into the surfaces and sensor, and raises it above 75C. Hence the cycling.

Tom T.

[quote]Originally posted by Robin 993 DX In Atlanta:
<strong>
So that which may explain why your engine aux. fan is running when you turn the key on.</strong><hr></blockquote>

Hi Robin,

You are very likely correct....I plan to try it out tonight with the air temp **** on full cold at first, then full hot, to see what happens. Then I will find the relay, pull it, and jumper the terminals to verify low & high speed fan
operation. Finally I will try to locate the air temp-sensor. Will let you know my findings. Thanks for the help!

Tom

Buck

Update #2:

The fan had cut off after I re-connected the battery (Sunday night) so I thought I was OK. But, after sitting for a day the battery was drained. I have since talked to a couple of shops and both told me they have had to replace the Air Temp Sensor because of similar problems. I have ordered both the Air Temp Sensor and the Resistor (don't think it's the resistor but since I was changing things and it's cheap).

Here are the part numbers for future reference:
- Air Temp Sensor = 964.659.120.00 ~$28.00
- Resistor = 964.616.550.02 ~$17.00

They are both very easy to get to. The Air Temp Sensor is on the aft side of the black air tube on the left side of the motor. It's the first thing you see when to look at the air tube. To remove it you just twist it 90 degrees and it pulls right out. Remove the spring clip and the sensor unplugs from the wiring harness. The Resistor is on the same tube but on the lower left side. It just snaps out.

I'll let ya'll know if the Sensor or Resistor fix the problem.

Thanks

Rocket

I took my car into a OPC and they thought everything worked fine!

Time to sort it myself

Thanks Randell ...once I found the relay will do the jumper test.

Tom T......my symtoms are similar to yours.

Engine cold ignition "on" = no fan unless temperature control above 21 then slow speed fan.
Engine hot ignition "on" = high speed fan with temperature control at minimum.
Engine hot ignition "off" nothing even after several laps of a track.

Robin.....does this help diognose the fault?

Buck.......keep us posted. I think I might change the sensors like you. I assume the relay for the fan is hiding in the box adjacent to the fan housing in the engine compartment?

Rocket

Robin 993DX

Rocket,

Sounds like it is working just fine.

grungyspeed

Wow Hank,
I had the exact same progression of problems when my wiring harness went bad. I thought they were random..

Tom T.

[quote]Originally posted by Rocket:
<strong>
Tom T......my symtoms are similar to yours.

Engine cold ignition "on" = no fan unless temperature control above 21 then slow speed fan.
Engine hot ignition "on" = high speed fan with temperature control at minimum.
Engine hot ignition "off" nothing even after several laps of a track.

Rocket</strong><hr></blockquote>

Took my 993 out tonight to test this problem out. The engine aux fan worked exactly like Rocket described above. After I figured out which sensor is the temp-sensor I unplugged it and the fan ran continuously. Then I twisted it 90 degrees and pulled it out. In it's place I inserted a cooking temperature probe hooked up to my digital cooking thermometer to measure the engine air temps. My reading was 120F which is higher than the 113F/45C temps Robin mentions that would trigger the fan. The p/n of the temp sensor is the same as Buck's. I'm guessing that this is the culprit but w/o a way to measure the sensor there is no way to be sure.

Maybe some of you can unplug the sensor connector to see if your fan runs (not sure if would really prove anything though)?

Buck - please keep us posted with your results of the new sensor and resistor.

Tom

Rocket

Changed the temperature sensor and resistor today, made no difference to the fan operation i.e. it still doesn't operate with the ignition "off" when the engine is hot.

Tom .......I can confirm that my fan runs continuously at low speed ignition "off" with the sensor unplugged.

Are there any wiring diagrams available over the internet that cover this area. I don't have the workshop manuals myself?

It seems strange that a temperature sensor located in a plastic pipe in the blower air intake/extract should be used to measure an increase in engine temperature. Surely a sensor located on the engine block/head would be better able to measure engine temperature. My question is whether there is another sensor, and if so where is it? Its possible we are barking up the wrong tree.


Rocket

Randall G.

Hi Rocket,

Here are resistance values for the air temperature sensor at the rear fan (from the shop manual):

0C (32F) = 28.8-36.4 kohms
25C (77F) = 9.0-11.0 kohms
50C (122F)= 3.1-4.0 kohms

As you can see, no value is give for 75C. Also, the sensor is not linear.

Anyway .... we know the CCU is looking for some low resistance (low resistance = high temperature) before it will run the fan in fast-speed, ignition off.

If you have a small resistor around the house--say 100 ohms??--try placing it across the contacts for the sensor. If the fan fires up in fast-speed, the rest of your system is probably okay.

Alternatively, you could try removing the sensor from the duct, but leaving it plugged in, then heating it with a blow dryer until the fan decides to start in fast-speed (just be careful not to melt anything ).

I think it's possible there's nothing wrong with your aux. blower engine-off cooling function. 75C = 167F is pretty warm, and I think it's quite possible the air isn't getting that hot.

Rocket

Hi Randall........Heated the sensor up with a hairdry as you suggested and low and behold on comes the fan without the ignition on.

Like you say must be working fine, unless the old sensor was duff.

I wait with exitement to see if it works for real.

Many thanks

Rocket