Volvo: 1999 xc runs rough when ac is on, blown head gasket, coolant temp

Question
QUESTION: My v70 xc runs fine for a while but when the ac is turned on it begins to run rough and smoke.  If I reset the computer it begins to run smooth until the AC is turned on.

ANSWER: Shan,
It sounds like the A/C compressor is beginning to fail. Especially sice the compressor smokes. Bring the car in to the shop and have it tested before bigger problems occur.

---------- FOLLOW-UP ----------

QUESTION: Thank you, Smoke is coming from the tail pipe, could that be related to the compressor?  My mechanic changed out the mas air sensor today.  No change in symptoms.  He thinks the computer is adjusting the richness of the fuel in reverse.  In other words richer in heat and leaner in the cold.  Does that sound likely?

Answer
Shan,
I do not think smoke for the tailpipe in this case means anything that could relate to the compressor. If the smoke is blue, that is burning oil, if the smoke is white that could be condensation in the engine, exhaust system or burning coolant. If the car runs rougher with the A/C on then that is the load from the working compressor. That should not affect engine running. However you say that it is, so the extra load on the engine is causing rough running. I would think there should be a fault code or two posted. Have the faults read and see what they are. You may find that there is a blown head gasket if the engine is burning coolant. Adding the load of the A/C takes some of the engine power and runs rougher. All this is not lining up properly, you are missing something. Find a shop that knows the Volvo and works on them daily to have them drive and run this car. How is the power in this car when driving? What is the compression? What codes are stored in the system? Does it run hotter than it did before all these problems? Is the engine really running rich what is the H/C and the C/O reading at the tailpipe? If it runs rich hot and lean cold do you have a coolant temp sensor out of range?