if its blowing, but not blowing cold its low on coolant. it takes r134a.
If it does blow just not cold air you should see if it needs to be recharged
tad bit low on freon.
Cause its broke!
because you need to keep warm when it is winter and other times when it it cold
Check temperature control cable for binding.
Low refrigerant causing compressor not to start?
How cold is it. Most diesel engine do not responed properly when the engine and fuel is cold.
The blower motor could be shot, or a fuse could be bad. A wire could be disconnected.
low refrigerant. stored liquid refrigerant boils away after 2-3 minutes, suction pressure drops, compressor shuts off on low suction pressure.
you may not have the heater water hoses plugged in
check your coolant level
think about it they have independent control thus they have separate cooling systems