[BoxsterSteve]

I use this trick to monitor coolant temp in real time.

Car diagnostic tricks which work on 1997- 2000 Boxsters.

There is some sort of serial data stream or CAN interface that allows the AC (manufactured by Audi) unit to display engine parameters. Here is a list of what can be seen:

To switch from F to C:
Hold down the recirculating button then push both the temperature + - buttons.

To access diagnostics:
Hold down the Recirculating & Air up buttons for 5 seconds.
The + - buttons go up and down through the list of "c" codes.
The center vent button switches the left display between the "c" code and its actual value.
Press the Auto button to exit.

0c - ERL
1c - Oil Temp
2c - Inside temp. Sensor mounted in the aspirator assembly at the side of the dash.
3c - Outside temp. Sensor located inside the air inlet of the A/C unit.
4c - Outside temp. Sensor located in front grill of the radiator. The data is fed to the climatronic from the instrument cluster. When not moving, the instrument cluster OBC temp display retains it's last setting until moving. This is to prevent heat emanating from the radiator affecting the temp. sensor. The A/C unit uses the lower of the two outside air temp values in determining fresh-air temp.
5c - Outside temp. (matches with OBC outside temp display)
#################
6c - Coolant temp.
#################
7c - Footwell discharge temp.
8c - Sun sensor (dash top)
9c - Sun sensor.
10c - Passenger compartment fan speed.
11c - Passenger compartment fan voltage.
12c - Temperature mix Flap command 1=COLD, 100=HOT
13c - Temperature mix Flap position
14c - Central Flap command
15c - Central Flap position
16c - Footwell/Defrost Flap command
17c - Footwell/Defrost Flap position
18c - Recirculation Valve command 1=OFF, 100=RECIRC
19c - Recirculation Valve position (feedback)
20c - Vehicle speed in kph, updating only once per second. (real speed, not speed+safety margin as in the speedometer)
21c - Engine RPM in hundreds. This too only updates once per second.
22c - ?
23c - ?
24c - Sun sensor, exterior lights switch & panel lights control (term. 58 & 58d voltage) - used for A/C panel display illum.
25c - ?
26c - ?
27c - ?
28c - Fan speed?
29c - ?
30c - Engine run time in seconds (255 max.)(=0xff)
31c - Timing counter
32c - Displays test
33c - Software version? Mine states 3.4
34c - ?
35c - Outside temp. from inlet sensor (filtered?)
36c - temp?