First figure out exactly what's it's doing to give you the Hot-Cold
swings, then you can figure out how to cure it - Is the AC Compressor
running constantly, cycling on and off, or not running at all?  Engine
temperature gauge steady of bouncing?  Heater hoses hot (open heater
valve) or not?  Can you see the heater valve linkage to tell whether
it is cycling?  How about the blend doors, Heat/Defrost/Air door or
the Fresh/Recirc door?

 My first thought is the radiator coolant level is way low, and you
have air pockets cutting the heat flow intermittently.  If the cab
temperature control panel is sending signals to the AC compressor and
heater valve alternately, it could be the cabin temperature sensor is
bad and giving it a comfort temperature target that keeps moving...

 Another thing that the dashboard controls like to do is get cold
solder joints between the circuit board and the potentiometers and
switches.  If you can push on one corner of the Fan Speed Switch or
the Temperature Slider and everything returns to normal while you are
pushing, pull out the controls and resolder everything.

 Give us a bit more to work with here.

 You are supposed to restrict the snarky one-liners to alt.hvac,
where the norm is to treat everyone like they're trying to take the
bread out of your mouth.

 Over here, we try to give honest and useful answers...  ;-P

  --<< Bruce >>--

LOL... the alt.HVAC newsgroup is beyond useless