Volvo FM Handbook page 350

MCC & HEAT
11 Set the temperature with the thermostat. The green
indicator lamp lights up when the heater is switched on
and the cab fan is running (warming-up phase).
Start engine heater only
ECC
Start the heater as normal, but set the temperature
control to blue, the coldest available. The cab will not
be heated, only the engine.
MCC
Turn the thermostat to its lowest position.
Cab 339
J8008250
J200697
J200698