Checking Regulating Quality and Heating Output

Checking regulating quality and heating output





Conventional tools




Digital temperature measuring instrument with 4 measuring probes
Robbitemp (90020)
Air temperature measuring probe (90023)
Supplier, e.g.:
Switzerland: Kent-Moore (Europe) AG
P.O. Box, CH-6340 Baar
Germany: Kalte-Fischer
Postfach 266, Augsburger Str. 289 - 291
D-70327 Stuttgart




Digital temperature measuring instrument with 4 measuring probes
Therm (2263-2)
4-fold measuring point switchover switch (2235-4)
Air temperature measuring probe (W 453-5)
Supplier, e.g.:
Germany: Ahlborn Mes- und Regelungstechnik
Eichenfeldstr. 1-3,
D-83607 Holzkirchen


Note: Do not carry out test in the workshop, but on the cool vehicle which has been allowed to stand in the open overnight. Interior temperature < 20°C.


Test conditions

1 Outside temperature < +15°C.

2 Driving time up to the start of the measurements approx. 10 minutes. With outside temperatures < 0°C a longer test drive is required.

3 Windows and sliding roof closed.

4 Do not allow engine to run up to operating temperature beforehand.


A. Checking regulating quality




5 Attach measuring probe to sun visor (right, arrow) and connect to measuring instrument. Then switch on measuring instrument.




6 On the pushbutton switch (b) select the function "lower vents" and on the blower switch (c) the function "Auto".

7 Switch off switch (S24, fresh air).

8 Close center nozzle.

9 Set temperature selector wheel (a) to 22.

10 Start engine and drive away immediately (approx. 50-60 km/h).

11 After approx. 10-15 minutes, read temperature on measuring instrument. Nominal value 22 ± 1 °C. If the temperature is not achieved, check heating output or check electric components of the automatic climate control.


B. Checking heating output




12 Fit one measuring probe (arrow) each into the left and right defroster nozzles.

13 On the pushbutton switch, switch on the function "defrost".

14 Allow engine to run at operating temperature with approx. 2000/rpm for 5 minutes. Nominal value: > 55°C.

Note: If the temperature is not achieved, check function of circulating pump. If o.k., renew mono valve for trial, flush cooling system if required. If this does not help, replace heat exchanger