92 5.0stang

My a/c does work when i start my car and it blows cold air and everything. but it only does it until the car is warmed up. then it stops blowing through the vents and starts blowing though the big vent under the dash on the passenger side. when i pop the hood the lines on left of the engine are all frozen over and so is the cannister frozen over. ive replaced the lines and the plug ontop of the cannister already. any ideas.

RUDEDOG.357

sounds like you a/c is icing up. its probably the low pressure switch not cutting out the a/c compressor when the pressure gets low. next time you start your car with the a/c ck that the compressor cycles on and off. if its on all the time the switch probably bad.

mjr46

you can nor diagnose an a/c system properly without gauges hooked up to high and low sides to monitor what is going on...........as for the air flow switching vent, you have a vaccum issue, whether it's a bad check valve a faulty resevoir you'll have to trace lines and check vac canisters for register doors....fyi, icing often occurs and doesn't always indicate an issue but heavy icing in a localized line could indicate a restriction at that point, such as a restricted orifice tube, and it would show on the gauges by the low side being pulled into a vaccum, most likely not a bad switch

lxman1

It's backflowing air out of the inside air duct (max a/c) because the evaporator is iced over solid and the air had nowhere else to go.
It definitely isn't kicking out on low pressure, so either someone has jumped out the low pressure switch on the dryer or it is stuck closed and needs replaced.
It is probably low on freon, but you will need to fix the problem of why it isn't kicking out first.

mjr46

I have a few probs with what you state, NO. 1 the op states the air flow goes from the vents to the floor vents, if you know how the case on a fox is designed and I have one sitting on my garage floor the blower motor connects on the end of the case before evaporator so all air flow must go across the evaporator if evap were frooze over air would not come out the floor it would backfeed out the fresh air by cowl........NO.2 if the freon were low the system often does not ice up even if the switch were jumped as there wouldn't be enough freon flow often for operation to occur...............Now if th OP means that air is blowing out the recirc door controlled by a vac motor and open when a/c is in the max position then back flow could occur if the evap were froozen up, to determine if such were the case shut a/c off for 5-10 min so it can defrost, however if it is icing, IT often is a result of a restriction or a problem with the orofice tube or a overcharged system.........either way OP you need to get a set of gauges on it and see what the pressures are doing

92 5.0stang

it looks as if the person before me rigged the compressor power so that it comes on when the engine turns on , so it is always running. but if i disconnect the rigged cable it doesnt run at all.

mjr46

then you need to put it back to factory design, cause always having the compressor running would cause the evap to ice up, now with the additional info you provided , we can say they may have done such due to a bad switch

92 5.0stang

wat exactly would be factory design............. and where is the switch. if its the switch thats on top of the accumulators i already replaced that

92 5.0stang

also idk if this will help reslove the problem. since the compressor is always running when im driving and i have the a/c on and i get my rpms up my a/c pretty much shuts off and it starts coming out of the vents by the windshield and the floor vents. it does this even when i turn the a/c off.

mjr46

then you have a vaccum issue in regards to the register doors changing flow, the line comes in throught the fire wall by evaporator lines out under the hood, check all lines for leaks