What could cause a popping sound coming from around the A/C compressor when I turn on the air condition. Seems like a overpressure. What could cause this? .

sounds like an air conditioning issue if your only complaint is the fans not coming on when air conditioning is used. you need to have the a/c sys checked out to see if you have a leak or perhaps refrigerant may be low. sometimes you may have a compressor that no longer works so the system may not be building up pressure so the pressure switch does not cycle the fans.

First check that all electrical connections to/from your air conditioning components are tight and secure with no broken or chaffed wires and connectors, or oil swollen connection points. Then check that all fuses and relays involved in the operation of your air conditioning system are operational. If all is good, then remove the belt around the air conditioner compressor pulley. Get a wrench and try to turn the front of the compressor pulley. It should turn with little to no resistance. If it wont move or is very hard to turn, it is probably locked up and needs repair or replacement. If it moves, then the compressor part is OK, but your clutch would likely need replacement. Some model cars its cheaper to just replace the whole compressor than to rebuild the clutch. Jaguar sounds expensive - I would seek out a junk yard. Good luck.

Take it to have the A/C pressure checked to be correct. Overpressurizing the system will keep it from working properly, as there is a HIGH-pressure switch that will shut the compressor off. You may have added too much refrigerant.

If it is affecting the engine performance, it could be a problem with the compressor.

The a/c compressor clutch might have locked up it should be free spinning when not engaged but could cause a belt to squeal and possiblly break if locked up

air conditioning compressor clutch has failed Need new compressor assembly

There are two possible sources for this; the auxiliary fan is not turning on with the AC and/or the compressor load on the belt (if shared with the water pump) is causing it to slip causing the water pump to lose revs. and water flow.
Have someone turn on the AC while you watch under the hood. You should hear a 'click' as the AC compressor clutch engages and the extra fan should turn on.

Put a new belt on it and spray the condenser coil in front of the radiator with a hose when it gets up to temp or the sound starts and see if it stops. Thats what I did today. Flapping/clacking stops for about 10 minutes until thing get hot again.A/C blowing cold air the entire time.

Weird, usually the pressure cut out switch, if you manually "bridge" this (only briefly say 4 secs) the a/c should work, sometimes a plugged/blocked condensor or evaparator will cause this . Also look at engine related temp switches, example water, as these are designed to overide and turn off the ac if the car gets too hot etc.
1)Bridge switch
2) ? oil level in compressor (seized??)
3) temp switches,
4)double check that the system is not blocked, coz if it is then the compressor will only go briefly and then stop due to "overpressure"

Sounds like you are on the right track. Jump the pressure switch and see if the compressor comes on.