AC cools then blows hot air, tempature needle goes up & down

was system evacuate by pumping it down using vacuum pump to remove all moisture out of the system.most time of the time when i work on AC system you have pump it down from 30 minutes to a hour.pump it until low pressure gauge read 30 hgs in the green area.i shut down vacuum pump close off manifold gauge valves see if low pressure side reading stay at 30 hgs or drop if gauge needle stop dropping have leak in the AC system.if all is good you have temperature air door problems.air door not opening all cool air to circulate through AC vents.

Hi, Yes you have an air lock in your system, you may get this sorted by 1/. Removing one of the cooling hoses & try to blow with air.
2/. Drain all the system then put your heater on inside the vehicle & have the engine running & refill the system Start to do this from a cold engine. Please leave me feed back: Malcolm Campbell, Thanks.

Is the compressor running when it blows hot air ?

If it has dual zone temp. control it is most likely the heater control panel.

you say it will blow cold and hot air for only a few minutes. You don't say but I assume you mean will blow cold a few min. when turned on AC max , blow hot only a few min. when turned to heater hot. Assuming thats the situation and you say AC charged and shows good on the low side -you should charge the AC to a full charge on the low side will cause problems with the AC air compressor kicking on and off. I suggest while the engine is running and turned to AC cold max watch the AC air compressor clutch to see if it does indeed kick on and off if so charge completely. As far as the heater make certain you coolant is all the way to the top and the best way to do this is when engine is completely cold remove radiator cap and fill completely and completely close cap then fill overflow container just to the cold level. That should fix your problem.

is the cooling fan on the radiator running? the high pressure will skyrocket if the fans are not working.

you have moisture in the system this causes your expancion valve to freeze up an stop working, thats why it works for sort time and when it de-freezes stars working again. you need to do a EVAC & RECHARGE with a good AC service equipment, specially attention to pull vacumm por at least 20minutes so you get all moisture out of the system.
Good luck

your electric fan for the AC is not working for whatever reason so when idles its all getting hot the engine and the AC system .This sort of work can be difficult to diagnose correctly and a code reader is about as good as a bible at mosque so seek the advice of a skilled mechanic who should be able to pin point the fault in seconds

WELL TURN ON AC MAX COLD HIGH TO SEE IF COOLANT FANS TURN ON.IF NOT YOUR REFRIGERANT SO LOW THAT THE AC REFRIGERANT PRESSURE SENSOR WONT CLOSE CIRCUIT TO TURN ON COOLING FANS.MEANING YOU NEED HAVE AC CHECKED AND CHARGED.ALSO CHECK COMPRESSOR FOR POWER IF NOT YOU HAVE BLOWED FUSE OR BAD RELAY.IF FUSE AND RELAY GOOD YOUR AC COMPRESSOR CLUTCH COIL OPEN OR THE AC CONTROL SWITCH IS BAD.IF COMPRESSOR IS RUNNING WHEN YOU TURN ON AC YOUR AIR TEMPERATURE ACTUATOR NOT WORKING.

You likely have a restriction in the heater coolant hose circuit - perhaps a coolant control valve not fully opening, or a kinked hose.
Insufficient coolant volume is flowing to keep the heater core hot.
Try back flushing the heater core system with a garden hose to check flow.