|
|||||
| |
|
|
|
|
|
The "REST" Menu Feature of the Climate Control
These are for the W208, other models may differ. After you get home from a drive (20 minutes or longer), let the car idle for 60 seconds while in park with the AC on. Press and hold the "REST" button on the climate control. After approximately 5 seconds, the display will change. You can now release the REST button. The left "auto" button will allow you to scroll through the menu.
Here are what the codes mean (W209 also has the red options):
01 The in-car temperature sensor.
02 The bumper temperature sensor.
03 The temperature of the left side heater core.
04 The temperature of the right side heater core.
05 The temperature at the evaporator sensor.
06 The engine coolant temperature.
07 The barometric pressure of the Freon.
08 The Freon temperature.
09 Blank.
10 The voltage at the heater blower control (normal is 08-6.0, which is .8 to 6 volts).
11 Emissions sensor voltage (to detect atmospheric gases and recirculate interior air).
12 Sun sensor voltage (to shift airflow in car).
20 The current at the auxiliary fan (the electric fan on radiator, in milliamps or mA).
21 Engine speed (x 100 RPM).
22 Vehicle speed (km/h or mph depending on installation).
23 The percentage of battery voltage at terminal 58d (a percentage of total voltage, 99.0 = 99%).
24 Battery voltage (e.g. 12.8 = 12.8V).
40 The climate control software version. - V8
41 The climate control hardware version. - V5
Either turning the car off or pressing the REST button again will take the HVAC out of diagnostic mode.
Some notes.
Common problems that can throw the Electronic HVAC for a loop are bad temperature sensors.
Naturally, if the in-car temperature sensor (#1) is broken and reads low, the AC will cycle off early while in auto mode. If it’s broken and reads high, you may freeze to death while in auto mode.
The evaporator sensor (#5) should be close to the in-car temperature sensor while the A/C is off, and a lot lower while the A/C is on.
The Freon pressure sensor (#7) is a good way to determine whether the Freon is low. Low refrigerant pressure commonly causes the left side to blow warmer air than the right side. Of course, the logical question is, "What’s normal?" My Freon pressure sensor (#7) reads as follows - when the car is started, and the AC is turned on, without touching the gas, it’s as high as 15. It drops to 7 while driving, and is commonly at 11/12 while waiting at lights.
Assuming the heater is not on, the left and right heater cores should be about the same temperature. If one is higher than the other, and it’s higher than the temp in the car, the Duovalve may be sticking. Low refrigerant pressure (#7) can cause the left side to blow warmer air than the right side, but low pressure shouldn’t cause the air on one side to be warmer than the outside air. What’s a Duovalve? Read about it here.