Cadillac: Air conditioner and heater, vacuum hoses, vacuum leak

Question
I bought a 1990 Cadillac DeVille a couple of years ago.  The air conditioner was working fine during a trip and then all of a sudden it started blowing warm air.  The compressor clicks on for a couple of seconds and then clicks off again.  The fan works fine both on the a/c and the heater.  The heater doesn`t seem to get as warm as it should.  When it starts warming, the temp. gradually changes to the temperature of the car.  Not warm at all.  I was wondering if these two things were connected in any way.  

Answer
Well the heater itself is probably OK since it has no moving parts and is just a small radiator that has air blown through it.  What this problems sounds like is a possible vacuum leak, if the A/C doors work on vacuum.
I had a wierd problem like that on my Seville, under medium acceleration the sound of the Air coming out the vents would change to that of the heater sound, and warmer air would come out until you let off the gas a bit.  My mechanic checked all the vacuum hoses for the A/C doors that direct the air to different places and found a leak, fixed it and now no more problem.  Your problem sounds like it's that kind of problem or something physically wrong with the air diverters inside the A/C system.

Although, it is strange the compressor only stays on several seconds.  That is usually a sign of low pressure in the system, but Cadillas usually turn off compressor if the pressure is low so you won't ruin the compressor.

You should have the system pressure checked, and if it is low, add freon.  If that does not solve the problem then I would investigate all of what I mentioned above about the A/C doors and all that good stuff.

Hope this helps.