I just recently had this problem for over a couple of weeks now. I have a 2006 S60 2.5T with 103K miles on it. Everything runs fine except I have NO heat in my cabin when I crank it high. Just cold air! Here's is what I've noticed:

1) On very cold frigid days (-5 to 15 degrees F) the temp gauge is ALWAYS at the cold mark. Never moves at all even after 30 minutes of driving! I know the needle is suppose to be at the 12 o'clock mark after a few minutes of driving but not mine.

2) On less frigid days (+20 to +35 degrees F) the needle does moves into the 12 o'clock position and I have heat!

I want to take am educated guess and say that it's the thermostat but something tells me that it isn't because if the thermostat is kaput, I shouldn't be able to have any heat at all. But, I do get heat, only at certain outside temperature. Anyone here have this issue before? Any help would be greatly appreciated! Thanks in advance!

 

For lack of heat start with the thermostat. You want to be sure that the system is working properly before you start hunting any other problems.

 

How can I tell if thermostat is the culprit and not something else? Is there a way to find out without diagnose machines?

 

Everything points to the thermostat in this case. If it is stuck open it never allows the engine to reach operating temperature thus never providing the heater core with hot coolant from which to deliver heated air. The fact that you get heat when the outside temps are above 20F means that the engine is capable of warming all the coolant in the system at warmer temps, but not at the colder ones.

 

What you said makes absolute sense and I have similar responses from another Volvo forum. I went ahead and ordered a brand new unit as a replacement. I'll just have to wait when the outside temperature is more manageable for me to do this. The mid-west has been in a deep freeze the last couple of weeks and this is why I wanted to take care of this matter as soon as I can. Thank you for your advice and inputs!