After exhausting other possibilities, we concluded (see above) it must be the servo motor or linkage which I did not want to replace by myself. So we asked a Volvo mechanic to change it and he did it successfully for about $550. That solved the problem. The 960 now has heat! So that credits the ECC ...

Found only one external ambient temperature sensor under the radiator hanging off a cable. The sensor was tucked inside the frame support just under the radiator on the driver's side. Disconnected and bench-tested it in the same way I tested the in-vehicle sensor. It's good. See graph of its tempera...

Lindy, Thanks. I have eliminated the in-vehicle sensor as the problem. I checked the vacuum tube connected to the dome light sensor and felt a vacuum pull when the vehicle is running so that means interior air is being sucked over the sensor. Next I removed the whole dome light assembly and connecte...

It's October in MA and time for heat but our 1997 960 has no heat. This just occurred, it was working fine a week ago. Symptoms: The vent blows only luke warm air regardless of setting. (The A/C hasn't worked in years but that's not the problem.) With the fan on auto the fan speed automatically incr...