What controls the air duct temperature?
 

Does someone here know what controls the temperature of the air in the cabin air vents? My 2006 V70 seems to have trouble regulating it. I either get lots of hot or cold, but no inbetween.

Is there a thermometer in the pipes somewhere that might be dirty?

Thanks

Pulls a little cabin air through a little vent in the front of the HVAC panel. It can get clogged with dust, but your problems are likely bigger than that.

Any brainstorm ideas as to what it might be?

BUMP - I have also noticed that for periods of time (minutes), the blend motors will constantly cycle from cold to hold to cold to hot etc. with a period of about 5 seconds. Any ideas?

Just found this. Maybe it will help someon else too.

A/C - Vent Temperature Cycles From Hot to Cold

NO: 87-54
DATE: 11-30-2005
MODEL: S60, S80, V70, XC70, XC90
MY: MY05 MY06
SUBJECT: Temperature Coming Out of the Climate Vents may Start to Cycle from Max Hot Back to Full Cold When Max Hot is Requested.
REFERENCE: VIDA
This Tech-net note supersedes the previous 87-54 dated 11-02-2005. Please update your files.
DESCRIPTION:
If the temperature knobs are turned to max hot, the temperature coming out of the climate vents may start to cycle from max hot back to full cold with a period of 4-15 seconds. No Diagnostic Trouble Codes (DTCs) are stored.
The number of steps on a temperature Damper Motor Module (DMM) may have increased from factory settings, causing the affected DMM to set a "not calibrated" flag to the Climate Control Module (CCM). This causes the climate system to self-calibrate over and over again resulting in the cycling temperature from the vents.
Attachment 21870
VEHICLES AFFECTED:
SERVICE METHOD:
The above mentioned symptom could be solved by a recalibration of the CCM.
For affected vehicles that are still in retailer stock, upgrade the cars during CPS or prior to customer delivery following the service method in VIDA:
1. Erase CCM DTCs.
2. Perform calibration of the CCM as follows:
- Select the "Diagnostics" tab followed by the "Vehicle communication" tab.
- Click the CCM box.
- Select the "Advanced" tab.
- Click "Checking LIN bus".
- Click "No" if no Damper Motor Module (DMM) has been replaced.
- Read and follow the instructions (to the right) carefully and click the VCT2000 symbol.
- Click the "Start" button (left on screen tool).
- Wait until status "Completed" is shown on the screen tool.
- Regardless of DTCs or no DTCs it is now OK to click the "Hide" button to continue.
- Click the "Continue" button to proceed.

3. Perform functional check of the climate system as follows:
- Start engine.
- Turn FAN speed to MAX.
- Select DEMIST and check airflow to windscreen.
- Select FLOOR and check airflow to floor.
- Select VENT and check airflow to dashboard vents.
- Turn to MAX COLD and check cold air from dashboard vents left and right.
- Turn to MAX HOT and check hot air from dashboard vents left and right.
- Turn temperature and fan speed controls to midrange.
- Select Recirculation and check difference in airflow noise in climate system.
- Switch off Recirculation and check difference in airflow noise in climate system.

4. Use VIDA to read CCM DTCs.
5. If CCM DTCs are present repeat step 1 to 4. If CCM DTCs are persistent after the third attempt, perform fault tracing according to VIDA.
Attachment 21871
EXAMPLE OF GRAPHIC DISPLAY IN VIDA OF THE PROBLEM
Attachment 21872
Warranty Claim Information