Volvo Repair: 98 S90 Erratic heat-Climate control, temp gauge, voltage values

Question
QUESTION: I have a 1998 S90. It has climate control, which used to work perfectly last winter. I recently replace the thermostat with a factory unit, as it was taking a long time to heat up. Now it heats up great and the temp gauge is back to normal. My problem now is that if I set the temp to 72 it gets way too warm (more than 72). If I lower it to 64-68 it gets cold. In other words it does not maintain the usual constant heat. Rad is full. Any ideas???

ANSWER:    Bill, check the cabin air temperature sensor. It might just be dirty or blocked too.

Happy New Year!

Mark

---------- FOLLOW-UP ----------

QUESTION: Mark-Thanks for the response. I have brushed the sensor on the dash, but it doesn't seem to have changed anything. Have you got any other ideas? Bill

Answer
   Nothing simple Bill. You need to test the output of the sensor with a table of voltage values vs temperature to be sure it is operating correctly. It's possible that you have a bad power stage also. It regulates the heat depending on the value from the sensor.


Mark