Does anyone know the temperature values that should open and close the air box valve? And what temperatures would one expect to be drawn in from the exhaust manifold in ambient conditions of 5 degees Celsius (about 35 F). If the ambient temp is this cold, will the flap always stay closed?

I took Volvodad's advice and inserted a Home Hardware digital thermometer in the box, to see if it was opening and closing. So far the evidence is at best inconclusive. Outside air is 5 degrees, intake air is 20 degrees, and engine is at operating temperature. This indicates that exhaust-warmed air is being used. When should the valve open to bring in cooler air?
Any help?
JD

JayDee,

The spec for the pre heat are 15 degrees C and above: intake gets cold air. 5 degrees C and below: intake gets full hot from exhaust.

The thermostatically-controlled warm air induction flap enables a constant air temperature of 70°F/21°C to be maintained throughout the system.

Check out Part Number: 1266826
info@fcpgroton.com
http://www.fcpgroton.com/volvo.htm
http://www.fcpgroton.com/volvo240b23fuelinjection.htm

Replace it. I did it to mine. The rack that it is mounted on is easily removed from the Air Box by squeezing the mounting clips together, carefully.

I suggest removing the whole Air Box, clean it all up, be sure the Pre-Heat Pipe is not broken and leaking.

Good luck

Thanks RLC
What these temp limits tell me then is that the flap will remain closed till spring. However, according to your description, the flap is not simply on/off, but rather mixes hot and cold air to maintain a steady temperature. Is this a correct summation?
JD

Yes, to keep a constant 70 temp.