Fresh air flap, or "it's foggy in here" (12/1/99)Add/read comments on the contents of this page.
Temperature regulating flap
Heater blower and heater core
Fixing the A/C Clutch Suppression Diode
(see also the Radio repair group)
Defroster/Econ = Humidifier ????
A broken recirculate flap spring is a common problem.
The recirc flap is accessed from inside the car. It's up behind the glovebox, which will need to be removed.
The spring is attached to a plastic plug in the flap which hard to reach.
The easy way to attach the new spring is to:
1. Remove the plug from the flap by twisting it a half turn.
2. Attach the spring with the plug in your hand.
3. Then re-insert the plug in the flap.
Attaching the other end of the spring was not a problem.
In some cases it's possible to re-use the old spring. If the end loop is all that broke off, which I think is typical, you can just bend the next loop up and reattach with it.
David Conner Columbus, OH
' 86 4KCSQ
Audi issued some technical service bulletins dealing with this repair; they are here:
Date: Tue, 18 Nov 1997 16:46:58 -0600
Subject: Re: quattro-digest V4 #1373
If anyone is interested, the negative temperature coefficient thermistor used in the 5k and 200 Audi (probably 100s also) is available from Digi Key in Thief River Falls, MN for approximately $2 each. As mentioned before, there are two thermistors used by the AC controller. It reads the two temperatures (resistances) and chooses the higher resistance (lowest temperature) to display. This is Audi's way of trying to avoid biasing the indicated temperature to a high value due to engine or road heat.
Anyway not all 1 k negative temp thermistors are equivalent. You also need to spec an R value that is the ratio of the resistance at 0 deg C (could be 25 deg C, I'm getting forgetful) to the resistance at 50 deg C. The Audi thermistor has an R of 9.1. If anyone wants the part number and the actual R value, send me EMAIL direct so I don't miss it and I'll send them to you. Also, the system will run fine with only one thermistor. So if you suspect a thermistor problem, try the system with only the plenum thermistor and then with only the front (behind grill) thermistor. It is unlikely that you have two bad thermistors, so one way should give you the correct temp. I replaced mine and am now within +/- 1 deg of actual (measured in the garage before the car is started) temp when ambient is around 25 deg C (77 deg F).
If you want to force the AC to operate below its lowest temp, you can find the wires going into the programmer and parallel a couple of resistors across the thermistor leads to fool it into thinking it is warmer than it really is outside. A single pole double throw switch could be easily wired so you can switch it on and off. You could even use microswitches that open and close with the activation of the defroster flap if you wanted. As a starting point, 2.2 k should make sure the indicated temperature is > 40 deg F.
Hope this is helpful.
Fred L. DeRoos
You can check the resistance of your sensors to see if they are out of spec... The resistance of the sensors follows a gently sloping, declining curve from:
~3300 ohms @32F
~2200 ohms @ 46F~
1500 ohms @ 59F
~1250 ohms @ 68F
~1000 ohms @ 72F
~ 800 ohms @ 86F
~ 650 ohms @ 95F
(This data is for the 1986-88 digital climate control, as per the Bentley)
Based on this, if you were sufficiently motivated, you could change the outside temperature that the control head sees and then verify it using the fault-code channels. Also, the A/C compressor clutch is regulated by the thermostat on the A/C evaporator housing. It has a capillary tube that's inserted into the evaporator and controls the power to the compressor clutch if the evaporator temperature falls below 32F, preventing ice formation.
The resistance values for this sensor are:
~ 40 ohms @ 59F
~38 ohms @ 68F
~36 ohms @72F
~35 ohms @86F
~34 ohms @95F
You'll need a good meter to measure this one properly. There is also an "Ambient temperature switch" that is _independent_ of these sensors located on the A/C evaporator housing. It opens when the temperature falls below 37F, interrupting a ground signal. The A/C control head will then prevent the compressor from being switched on.
Other devices that can kill the compressor are:
-A/C high pressure sensor (in plenum chamber, near left side of heat
-A/C kick-down switch on auto trans. cars - sends a ground signal to terminal 9 of A/C control head, turning the compressor clutch off for 12 seconds.
-Engine coolant overheat switch - sends a ground signal to terminal 20 of AC control head, which then sends a signal to A/C programmer to shut off the compressor clutch when coolant temperature rises above 247F.
Best Wishes,Alex'86 5KCSTQ
Date: Sat, 18 Apr 1998 08:03:30 -0600
From: "Fred L. DeRoos" <flderoos-at-mmmpcc.org>
Subject: Outside Temp Sensor
Hi Vince, I don't know which car you have, but for the 200 quattro there are two sensors used to display outside temp. One is located just behind the grill in the front of the car and the other is located in the plenum chamber below the windshield. The AC unit reads the two sensors and displays the temp of the coolest one. This is Audi's attempt to get around an erroneous temp from engine heat.
Anyway, the sensors are negative temp coefficient thermistors. As the temp goes down, the resistance goes up. They should each read 1000 ohms at 25 deg C. Audi wants approximately $100 each for them, but if you are able to do some soldering, you can replace them for less than $5. Digikey in Thief River Falls, MN sells the thermistors as part number KC016N-ND for $1.95 each. I think with shipping and handling, it comes to about $5.
If you want to look around for this thermistor, you need to specify one that is 1000 ohms at 25C with an R value of 9.10. The R value determines the slope of the resistance change with temperature. The old sensor can be dissasembled and the new thermistor soldered in place of the old one. Use a low wattage pencil iron as you can damage the thermistor with too much heat. Also, it will be necessary to slightly enlarge the plastic holder with a pencil so that the new thermistor will fit. This will be clear when you look at the old and new thermistors.
By the way, a quick test without measuring the resistance of the old
thermistors is to disconnect one of them and see if the temp reading is
now correct (with driving to make sure you aren't seeing engine heat).
If that doesn't work, reconnect it and disconnect the other one.
One of them is probably slightly high in resistance. It is unlikely
that both are bad. Good luck. Let me know if you need any more information.
Here is part of some information I posted to the qlist last year about the external temperature sensors:
To check the status of each sensor, you can read channels 4 (sensor in plenum) and channel 5 (sensor on cowl) on your climate control fault diagnostics readout. Compare the output to the chart in Bentley (D8-240) to get the temperature. Each reading should correspond (via the table) to a temp within about 5 degrees F of actual T outside.
BTW, the diagnostic readout values _decrease_ in a nearly linear fashion
as the temperature _increases_. Temperature of 50 degrees F gives a readout
of 127. The diagnostic number changes by about -1.4 units for every 1 degree
F increase. To a useful approximation (good to within about 3 degrees between
32 and 100F) you could relate T to the readout, D by the following equation:
T (deg F) = (198-D)/1.4
But beware that the accuracy is way off when much below 32 F.
BTW, in case I'm wrong about which channel reads which of the sensors, you can easily touch (warm up) the front cowl-mounted sensor and then quickly check to see which channel's value has become much smaller.
Phil Rose Rochester, NY
'91 200q pjrose-at-servtech.com
You got to love a $4.00 fix on a 20V. Especially when I was ready to toss around $150 into an A/C recharge. I can confirm the KC016N-ND part number as the correct one for the coupe 20V as well as the 200. Getting the sensor out of the plastic sleeve was a bit of a pain, I ended up sort of peeling it like a banana (cut all 4 corners and pried apart). After I stretched the plastic tube the sensor fit in, I pushed the new sensor in and taped the sleeve shut then pulled the rubber boot back over it....good as new.
Temperature regulating flap
The climate controller head regulates temperature by cycling the air conditioning compressor on and off (unless set to "off" or "econ"); by turning the flow of hot engine coolant to the heat exchanger core on and off via a valve located behind the engine head on the firewall; by closing the recirculate flap behind the glove box; and by controlling airflow using a temperature regulating flap. The flap is located under the hood, beneath the black plastic plenum on the firewall.
The climate control head controls an electric motor with a feedback circuit that tells the control head the flap position. I've found that if the electrical connection to this motor degrades, the climate control head cannot properly control the flap positions. You'll notice this when you get too much heat, or no heat at all. Run the climate control diagnostics (below) for details.
This motor has an audi part number of 443 820 511 A (Bosch 0 132 801 003) and runs around $70.
The fix involves either replacing the temperature regulating flap motor, or using electrical contact enhancer to improve the connection at the harness under the plenum.
Start by opening the hood, and removing the windshield washer arms (pull the protective caps, remove the 10mm nuts, mark the position of each wiper arm on the windshield, then bend each wiper at the joint and pull them off. Remove the couple screws holding the wiper assembly in place, and set it aside. (This gives you enough room to work, and only takes a minute to remove.)
This is a good oportunity to pull out the shop vac and remove all the dead leaves, small animal nests, and years of dust and debris. You'll need to make up a small diameter extension to get down into the bowels of the system; I used a paper towel roll cardboard.
Lube the moving parts/joints for the flaps. The motor is located on the driver's side of the blower box, above the glove box area. Follow the wiring back along the engine compartment wall; unsnap the connector, and use a good contact enhancer/cleaner; then reconnect. Now, start up the car, and run the climate control through the various settings and temperatures to make sure everything moves smoothly.
Heater blower fan, heater box, heater core
The fault system can be activated when the ignition switch is in the
position, the engine need not be running. The fault system is activated
by pressing the "OFF" button while holding down the "OUTSIDE TEMP"
button. After activating the fault system the "OUTSIDE TEMP" button can
be released. When initially activated the numeric LED displays will in-
dicate a code of `01. This value indicates the "channel" that is select-
ed for monitoring. Notice that the Climate Control system will continue
to operate in the mode it was in before the fault system was activated,
and it is possible to terminate the fault system display by pressing any
button on the head other than the "WARMER" and "COOLER" buttons.
The fault channel selection will increment when the "WARMER" button
depressed ... there are 22 fault channels. The fault channel value is
accessed by pressing the blue "COOLER" button. Once the channel has
been accessed it is possible to check other channels by pressing the
"WARMER" button. The channel definition is:
`01 System Faults (see fault code table below)
`02 Measurement value of inside temp sensor (roof mounted) (refer to chart in Bentley)
`03 Measurement value of inside temp sensor (dash mounted) (refer to chart in Bentley)
`04 Ext Temp Sens - Plenum
`05 Ext Temp Sens - Radiator
`06 Measurement value of coolant temp sensor G62, phase in during production
`07 Graphic Control Head Output for A/C programmer
`08 Actual value of feedback potentiometer for temp regulating flap servo motor
`09 Specified value of feedback potentiometer for temp regulating flap servo motor
`10 Specified Blower Motor Voltage
`11 Vehicle Voltage <=== Useful for monitoring battery too!
`12 Total of electrical system voltage interuptions, values between 5 and 9.5 volts (less than 5 read as open low-pressure switch)
`13 Program number (not significant for troubleshooting)
`14 Switch position of high pressure switch (0-5 means high pressure switch closed)
`15 Specified voltage on fresh air blower in volts (depends on program)
`16 Pulse counter (not significant for troubleshooting)
`17 Graphic display of compressor shutoff conditions
`18 Graphic display of electrical outputs
`19 Number of times compressor shut off via high pressure switch F118 (red housing).
`20 Number of times compressor shut off via high pressure switch F118 (red housing) since last ignition switch cycling. After 8, compressor shuts down until system restarted.
`21 Program number (no significance to troubleshooting)
`22 Speed signal
System Fault Codes for channel `01
00 - No problems!
`01 - Interior temp sensor open
`02 - Interior temp sensor shorted
`03 - Exterior temp sensor in plenum open
`04 - Exterior temp sensor in plenum shorted
`05 - Exterior temp sensor in front of radiator open
`06 - Exterior temp sensor in front of radiator shorted
`07 - Feedback potentiometer on motor for positioning heater flaps Open Circuit/interuption
'08 - Feedback potentiometer on motor for positioning heater flaps Short circuit
'09 - Coolant temp sensor G62 open circuit
'10 - Coolant temp sensor G62 short circuit
'11 - Inside temp sensor (roof) open circuit
'12 - Inside temp sensor (roof) short circuit
`13 - Battery voltage is/was less than 9.5v during current running period
`14 - High pressure sensor - Excess pressure in system, compressor off
`15 - Adjustment motor for temperature regulating flap with feedback potentiometer is set incorrectly
'16 - High pressure sensor - short circuit
Definitions for graphic control head output - channel `07
(I'll eventually add the diagram showing the various flaps and levers; for now, the text version will have to do)
When Channel 7 is read, each segment that is lit (or not) has a meaning,
1 lit or flashes: temperature regulating flap moves towards "heating"
2 lit: Recirculation fresh air flap is in recirculation mode
3 and 5 lit: "air from instrument panel outlets"
4 lit: Heater valve is closed
5 lit (but not 3): "air from instrument panel outlets and to regulating flap (footwell/defrost)".
6 lit: "air from footwell outlets"
7 lit or flashes: temperature regulating flap moves towards "cooling"
8 lit: compressor on.
9 lit: Radiator cooling fan runs on first speed.
When Channel 17 is read, each segment that is lit (or not) has
a meaning, as follows:
1 lit: compressor on.
2 lit: compressor off. A/C refrigerant high pressure switch (red housing) open.
3 lit: compressor off. Outside temperature too low, or mode = ECON or OFF (check outside temp sensors)
4 lit: compressor off. Electrical system voltage less than 9.5 volts.
5 lit: compressor off. A/C refrigerant low-pressure switch open.
6 lit: compressor off. Kick down function activated. (switches on after 12 seconds).
7 lit: compressor off. Coolant temp warning switch, or multifunction temp switch closed.
Testing air control doors - This is from the earlier system, and
may or may not be accurate for our cars.
If the diagram is correct, the same line that selects outside air or recirculated air
controls the flow of coolant to the heater core. The table below shows
actuator positions for several conditions.
Function | FRESH/RECIRC | CENTER VENT | DEFR/FOOT
| HEATER VALVE
OFF | RECIRC | CLOSED | WINDSHIELD | CLOSED
ECON 64F | FRESH(?) | FULLY OPEN| FOOTWELLS | OPEN(?)
ECON 84F | FRESH | CLOSED | FOOTWELLS | OPEN
BI-LEV 64F | FRESH(?) | HALF OPEN | FOOTWELLS | OPEN(?)
BI-LEV 84F | FRESH | HALF OPEN | FOOTWELLS | OPEN
AUTO 64F | RECIRC | FULLY OPEN| FOOTWELLS | CLOSED
AUTO 84F | FRESH | CLOSED | FOOTWELLS | OPEN
DEF | FRESH | CLOSED | WINDSHIELD | OPEN
Notice that I question a couple of the entries in the table in regards
to the heater valve being opened when the temperature setting is low.
I'm noting that here, because the heater valve servo and fresh air/recir-
culate servos are connected together. One important thing to note is
that the recirculate/fresh air door has only two valid positions ... if
yours appears to be somewhere in between it is an obvious fault. BTW,
the heater valve servo is open when the actuator arm protrudes from the
vacuum motor and the valve is closed when vacuum is applied to the motor.
Compressor rebuild Co.
7850 North Willis
Van Nyes, CA
818 908 9272
Subject: A/C clutch suspression failure.
The A/C clutch relay contains a supression diode to suppress the inductive
voltage spike generated by the clutch coil when the relay contacts open.
this diode is subject to infrequent (?) failure.
1. If the compressor runs all of the time rather than cycling
with A/C demand, the diode is shorted.
2. If compressor disengagement causes radio noise and other electrical
disturbances, the diode is open.
No need to replace the (outragiously priced) relay, just the diode
within the relay with any Radio Shack 2 amp, 50 volt or better diode, (not
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Add/read comments on the contents of this page.All rights to this info in this format are reserved; feel free to use it, but don't just copy it verbatim! Not responsible for screwups in typing etc. YMMV, etc. I haven't tried many of these procedures, and some are adapted from procedures for other Audi models.
Please send me any comments, updated procedures, etc.