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Climate Control Diagnostics and Repair

Climate Control Diagnostics & Repair

Heater Not Working

Heater Blower Motor Replacement

Diagnosis and Fault Codes

A/C Leaks

A/C Clutch Bearing

Outside Temperature Sensors

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Heater Not Working
There is a vacuum actuated heater (hot water) cutoff valve in the input heater hose, located in the engine compartment at the end of the engine block very close to the firewall. Looks like a plastic cone with a visible small actuator attached to a valve in the heater hose. It's function is to cut the hot water flow into the passenger compartment (heater core) when the air conditioning is working and calling for cold air (i.e. climate control in "auto" position and temp setting below the cabin ambient temp). Set climate control to "econ", temp to 85, and check to see that the actuator is extended away from the cone (a little finger help is acceptable). Test by hand feel to see if the hot water is flowing past the valve (after engine is hot, of course). If it does you probably had a sticking valve. If it doesn't, make sure the climate control is in "econ" mode, you may then disconnect vacuum line from the valve actuator (the cone), and plug line with a golf tee. If you can move the actuator away from the "cone" to the open position and the valve is not stuck, you will have heat in the passenger compartment, and maybe a sick climate control programmer. All above assumes coolant levels are ok.

Heater Blower Motor Replacement
Take out the glovebox -- look for the screws around the perimeter behind the glovebox door. You'll then see the fan mounting on the air plenum. Unscrew these screws and disconnect the power leads. Now, with a lot of wiggling, prying, and forcing, you should get the old fan out (there is just a little lack of room between the fan mounting and the local brickabrack)

Take a page from Audi Dudi's book "if it won't come out, remove something else". The trick is to remove the fan from the housing which holds it. Two screws hold the fan to a plastic housing. Remove these, pull the plastic housing off, leaving the fan inside the plenum. With a minor amount of wiggling, the housing will now come out. Then you are left with the motor and blower. They will also come out. This housing normally comes off with the fan, and taking it off first gives you just enough clearance. Reverse the procedure to install your new fan.

Diagnosis and Fault Codes from the Climate Control Head
22 Diagnostic 'channels' are available on the A/C control head.
(For diagnostic values greater than 199, the first digit is represented as a horizontal and vertical line or "arrow")

Pulling up the display:

  1. Ignition ON
  2. Push & hold the OUTSIDE TEMP button
  3. Push & hold the OFF button
  4. Release OUTSIDE TEMP button then the OFF button

Now you'll see a little vertical line followed by 01. (Looks like '01) This is you 'channel' display. You can adjust the channel by using the warmer cooler buttons on the control head. Once the display shows the proper channel number, press the OUTSIDE TEMP button to show that channel's value. End the session by switching to any A/C mode or switch the ignition off.

 

DIAGNOSTIC CHANNEL

CHANNEL DESCRIPTION

CHANNEL VALUES

01

System Error

00 = no system error
01 -- 16 = See error table

02

Measurement Value of inside temp sensor G86 on roof

Depends on temp. (table, Section D8-310)

03

Measurement Value of inside temp sensor G56 on instrument panel.

Depends on temp  (table, Section D8-310)

04

Measurement Value of outside temp sensor G57 (plenum)

Depends on temp  (table, Section D8-240)

05

Measurement Value of outside temp sensor G17 (cowl)

Depends on temp  (table, Section D8-240)

06

Measurement value of coolant temp sensor G62. 

Depends on temp  (table, Section D8-320)  Note: Display value for vehicles without coolant temp sensor  255 = open circuit

07

Graphic display of output control info for A/C programmer.

SEE  Sec D8-40

08

Actual value of feedback potentiometer on temp regulating flap servo motor, v68

Dep on prog:  Numerical value for the position of the servo motor is shown.

09

Spec value of feedback potentiometer on temp regulator flap servo motor

Dep on prog:  ONLY CHECK when value in CH 8 is between 30 and 200. 

10

Specified voltage on fresh air blower

Specified in volts

11

Vehicle Electrical System Voltage

Depends on instantaneous operating condition greater than 9.5 volts.

12

Total of Electrical system voltage interruptions - values between 5 and 9.5 volts.

Depends on running performance since display was last erased. 

13

Program Number

No determination... no use in troubleshooting

14

Switch position on high pressure switch F118 (red housing)

0-5 (high pressure switch closed)

15

Specified voltage on fresh air blower V2 in volts

Depends on program

16

Pulse Counter

No significance

17

Graphic display of compressor shut-off conditions

Depends on program see sec. D8-50

18

Graphical display of electrical outputs

Depends on program see sec. D8-60

19

Number of times the compressor shut off via high pressure switch F118 (red housing)

Depends on running performance since display was last preset.

20

Number of times the compressor shut off via high pressure switch F118 (red housing) since last ignition switch cycle or reset from OFF button

Note: After 8th shut off during a driving period, the compressor does not switch on again.

21

Program number

Not significant

22

Speed signal
Note: at high vehicle speeds fresh air blower speed is limited in "fresh air" mode

00 when vehicle stopped
01 or higher dependant on vehicle speed.

A/C Leaks
Symptoms: loss of R12 refrigerant, no more cold.
Could be Big Bucks for hoses, but most often seen is a leaky condenser, which can be welded for about $30, total repair including locate leak, weld, fill for around $220.

A/C Clutch Bearing
I'm not sure the following P/N applies to our compressor, but we do have a Nippon Denso:
AC Clutch Bearing (Nippon Denso): This double row ball bearing is made by Nachi, P/N NAC40BG05S1DS. cost is $21.50.

Eastern Bearings Inc.
7096 So. Willow St.
Manchester, NH 03103
603-668-3300 phone
603-669-5714 fax

the man to talk to or email is Tom Breault, Operations Manager

Outside Temperature Sensors
The following is from a 200Q owner, but it should apply to ours as well. The 200s use a pair of negative temperature coefficient thermistors to sense the outside temperature. One of them is located in the plenum below the window (under the hood on the passenger side) and the other is located in front of the AC condenser approximately in the middle of the car (attached to grille). Both thermistors are identical and are 1000 ohms at 25 deg C. They have an R value of 9.10 and can be purchased from Digikey Corp. in Thief River Falls, MN for approximately $2 each. The part number is KC016N-ND. The reason you are reading low, is that the AC head unit reads both sensors, then displays the one that senses the lower of the two temperatures. This is done to prevent the display of an artificially high temperature due to engine or sun heating. The temp may still be a little high, but at least it would be the lower of the two. The problem is when one of these sensors goes bad, it typically increases in resistance. That means that your temp display will show low.

The display will operate with only one sensor, so you can do one of two things. Best choice is to check the resistance of each sensor at approximately 25 C and see which one is reading high, then replace it. Second approach is to unplug each sensor separately and see which one makes the temp read correctly (assuming you haven't been parked in the bright sun or just run the car and the engine is hot. The front one by the condenser was bad on my 1990 200 TQ. When I unplugged it, the temp read ok, but often needed a few minutes of driving to blow air over it and reach a stable temp indication.

To replace the thermistor, you will need to remove the bad assembly, then remove the plastic tip from the holder. The original thermistor is soldered to the two wires and fits into a plastic tube. The new one is just slightly larger, so you will need to insert a screwdriver into the plastic tube and enlarge it approximately 0.02 -- 0.04 inches. Audi would be happy to sell you a replacement, however, they list for approximately $100.


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