Check the temperature control cable
That means either you have air in your heater core or your heater core is being bypassed
it could be either or if its R-12 it needs to be converted
You either have a bad a/c heater controller or a bad or weak a/c heater blend door..........
Either you badly need a refrigerant recharge, or your AC compressor is shot. Or both.
sell it
The air conditioner has failed in some way. Either the compressor has failed or the pressurized refrigerant has leaked out. DO NOT operate the air conditioning until the problem has been fixed, the refrigerant contains oil to lubricate the compressor, which, if the refrigerant has escaped, will be damaged without lubrication. Don't turn a cheap fix (refrigerant recharge) into a very expensive one (replace compressor).
The Heater core is Either clogged or has gone out. If so you will notice either a leak of antifreeze or you will smell it when you turn your heater on, and your clutch needs to either be adjusted or replaced depending on how long the part has been on your car
If it's not blowing ANY air at all, you either have a defective blower or severely clogged ducts. If it's not blowing COLD air, there's a vast number of possibilities for why this might be, ranging from low refrigerant, bad sensors, blockage in the AC system, a faulty compressor clutch, damaged fins on the condenser, etc. I'd recommend you have a qualified professional do a system performance test on your AC system.
your most likely low on refrigerant. the o rings and seals dry up with time and start to leak. you could also be having a blower motor issue. not blowing air across the evaporator coil. there are also vacume lines which could be off , causing the recirculator door or heater valve to malfunction. either way you should have a professional look at it.
If the system is short on refrigerant or has a leak the indoor coil will ice up and the fan will start spitting out pieces of ice, either that or the filter is really dirty.
If the system is short on refrigerant or has a leak the indoor coil will ice up and the fan will start spitting out pieces of ice, either that or the filter is really dirty.
Is it the early '99 mk3 or the later '99 mk4?? Either way you have to remove the I/P (dash) and heater box. On the Early 99 you have a large brace to deal with before removing the heater box. On either model the A/C refrigerant has to be recovered and that requires a shop with special equipment. Good Luck.