At 07:09 PM 10/15/01, Andy Williams wrote:
Hello All,
My '89S4 has performed almost flawlessly since purchase in 1998. It has
about 45k miles now. I'm now having some trouble with the cooling
system that appears related to the cooling flaps and electric fans. It
intermittently begins to run hot (needle to the red once), and I have
noticed that after stopping and checking under the hood, the cooling
flaps are closed and the fans are not running. If I switch on the A/C,
the flaps will open and both fans will run, quickly bringing the temp
back to normal. For this reason, I don't believe that I have trouble
with the thermostat or other water-flow problems. I've also noticed
that while stopped at times, the flaps will move around a lot, opening
partially, then fully, with the fans stopping, speeding up, etc, all
appearing to work randomly - i.e. sometimes the fans will be running
(A/C off) with the flaps closed. The flaps seem to do some sort of
stutter-step operation quite often.
I'm hoping that someone on the list can enlighten me on how this system
is supposed to work to assist me in my troubleshooting. Are the flaps
supposed to be continuously variable, or are there two or three distinct
operating positions? Are the fans designed to work independently from
the flaps, or should they always be coordinated? How does the A/C
on/off enter into the fan/flap operation? Where are the key temp
sensors that affect the operation? From other posts on the list, I
understand that there is one sensor on the top of the manifold, and I
assume that there is another in the block or in the coolant plumbing
somewhere.
===============================
There are three sensors for the fans/flaps:
Coolant temp sensor - located in the lower left forward face of the
radiator (Sounds as if this one might be your problem).
Freon temp sensor - located on top of the receiver/dryer.
Inlet air temp sensor - located on top of the manifold - mainly used for
cool-down after shut-down.
If the fans are off, the flaps should be 0% open (closed).
If the fans are running at low speed, the flaps should be 30% open.
If the fans are running at high speed, the flaps should be 100% open.
If the coolant is hot (over 85 deg C), the fans should be on full speed and the flaps should be fully open. Sounds as if there may be a problem with your coolant temp switch.
Wally Plumley
928 Specialists
===============================
Andy,
I have a problem with my flaps on my late 89 S4 (first of the digi-dash)
in UK although the sequence is different. My flaps and fans appear to work satisfactorily as long as the A/C is off. Having said that I will
check the sequence now I have read Wally's note as well as the two
references from Darren. As soon as I switch on the A/C, which in itself
seems to work OK, the flaps shut although the fans continue to run. They
shut sufficiently quickly that I cannot get from leaning into the car,
to operate the A/C switch, back to the engine compartment to see them
close. Could this be the the Freon temperature sensor?
My current temporary solution has been to disconnect the link from the
motor to the flaps leaving the flaps continually open and all seems
well. However I would like to reinstate them and would welcome any
comments. The only problem that I have noticed is a small tear in the
boot that covers the motor and one task this winter is to take the motor
off to see if the has been any water damage.
From Wally's notes it appears that the motor operation has three stages
- closed, 30% open and fully open or are these just particular positions
to illustrate measuring points on a smoothly variable opening motion?
When the flaps are 30% open I presume that the vanes are turned 30%
which is not necessary the air flow being 30% (or is it ?).
Interestingly this problem has been with the car since purchase but
disguised by other A/C problems that were solved by cleaning up the
outside air temp sensor in the cooling duct to the alternator. The
engine temperature is constant at one needle width below the second
white graduation without the A/C on and flaps connected, and with A/C on
and flaps disconnected. However with A/C on and flaps connected the
temperature creeps up and, on a warm day (we have them occasionally!),
it will get to nearly the red mark but has never gone to it. It also
seems that switching the A/C off does not open the flaps but stopping
and shutting off does reinstate the normal operation when the A/C is
off. Can't help but be impressed with the system that still has
sufficient cooling on a warm day (for UK that is) with the flaps shut to
prevent real overheating.
Any further comments Wally? Your input is read fanatically here and is
much appreciated.
Rod
===================
Definitely not the proper mode of operation.
The next test probably should be at the control box, which is located between the passenger seat and the door. I have a problem here - I don't know how the box is oriented on a RHD car. There are two plugs, identified as I and II. If you look down upon the box, with the part number visible at the top and the plugs at the bottom, the left plug is I and the right plug is II.
If you hold the disconnected plug so that you are looking at the connectors with the wire harness coming out at the top, pin 1 is bottom left, with 1, 3, 5, 7 going up the left side, 2, 4, 6, 8 up the right side. There should be a dot between 1 and 2.
To test the Freon sender:
Connect an ohmmeter between pin 4 of plug II and pin 7 of plug I and test
the resistance with the A/C running.
1.5 bar - 22 */- 4 ohm
5 bar - 53 */- 4 ohm
10 bar - 92 */- 5 ohm
15 bar - 125 */- 5 ohm
I doubt that the problem is the sender. Unless you have ready access to a
set of A/C gauges, I would suggest that you just check the resistance with
the A/C running, and see if you get 20 - 50 ohms at idle, and that the
resistance increases slightly when you increase engine RPM and hold it for
a moment.
To test the flap motor:
Use a jumper wire to connect pins 5 and 7 of plug I for four seconds. The
flaps should be closed.
Connect pin 2 of plug II to pin 7 of plug I for four seconds. The flaps
should move to the 30% position.
Connect pins 7 and 1 of plug I for four seconds. The flaps should move to
the 100% open position.
If the flap motor does not perform as specified, check the wire harness between the plugs and the motor. If it is good, the flap motor may be bad. If all of this works correctly, the control unit may be bad.
----
>My current temporary solution has been to disconnect the link from the
>motor to the flaps leaving the flaps continually open and all seems well. However I would like to reinstate them and would welcome any comments. The only problem that I have noticed is a small tear in the boot that covers the motor and one task this winter is to take the motor off to see if the has been any water damage. From Wally's notes it appears that the motor operation has three stages - closed, 30% open and fully open or are these just particular positions to illustrate measuring points on a smoothly variable opening motion?
----
These appear to be fixed positions. 0% is closed, 30% is about 10 mm
(memory here - don't take this as an exact spec), 100% is wide open.
Good luck!
Wally Plumley
928 Specialists
=====
There are three (five-speed) or four (auto) sensors for the fans/flaps:
Coolant temp sensor - located in the lower left forward face of the radiator
Freon pressure sensor - located on the receiver/dryer.
Transmission fluid temp sensor (auto only) - located on the transaxle
Inlet air temp sensor - located on top of the manifold - mainly used for
cool-down after shut-down.
If the fans are off, the flaps should be 0% open (closed).
If the fans are running at low speed, the flaps should be 30% open.
If the fans are running at high speed, the flaps should be 100% open.
If the coolant is hot (over 85 deg C), the fans should be on full speed and the
flaps should be fully open.
You could try a simple test. The next time that you drive the car long enough to
get it fully warm, just let it idle for a few minutes, then turn the A/C off.
The fans should still be running, at least at low speed.
If both of the fans run properly at full speed with the A/C on, the fans, fuses
and wiring are probably OK, and the problem is likely to be the radiator sensor,
with some possibility of it being the control sensor or the wiring.
Wally Plumley
928 Specialists
www.928gt.com