A/C stops blowing cold air after 15-20 min

[ec214]

2007 m35, my ac will work perfect at start up and then 15 - 20 min it will start blowing hot air.
If anybody has information on this please help me.
Thank you.

[TOMatBMR]

Have someone put some gauges on it. You likely have a pressure or switch issue that could be caused by any number of issues. How well versed are you on AC repairs? You almost always need a professional AC machine if you want the job done right.

[EniGmA1987]

Did you make sure your car is not starting to get close to overheating? That gauge is way off to the side and is kinda hard to notice at times. I had a problem once where the cold air would start blowing hot when my engine was getting too hot. It wasnt overheating or tripping any warning lights or losing power or anything, which is why it was a little unnoticeable for the first day. But I had a hairline crack in one of my radiator fittings (they are just plastic) and it had evaporated enough coolant out that the car was running hot, without being so low of coolant to cause overheating problems just yet. Anyway, when the engine is too hot the A/C starts blowing hot air instead of cold, and it takes 15-20 minutes for the engine to heat up that much when coolant is low. So check that gauge and make sure you are running at normal temp, which should be just barely below the halfway point. Hot air starts blowing when the temp gets about 3/4 of the way up the gauge.

[ec214]

Ok I made sure that the coolant was full, it was over heating. It helped a lot and it blows cold air for a longer time. I took it out of town today and it keeps heating up way too much where the ac will start blowing hot air again after maybe 45 min or so.
I check the level in the tank and the radiator and it's full.
I did notice that it only over heats when u turn the ac on. But as long as I have it off everything is fine..
Anything will help. Thank you again for the advice

[MaxBolus]

Have you had your A/C refrigerant level checked? If I recall, low refrigerant can cause evaporator icing, which will stop the cold air from flowing. Do you notice a pool of water under your car when you use the A/C?

just thoughts..

cheers

[EniGmA1987]

if the engine starts to overheat only when the AC is turned on then maybe something is broken with the AC unit. Cant say for sure but the engine drives the AC through a belt. I believe when the AC engages a clutch engages and mechanically connects the driving belt to the AC compressor, so it could be the compressor needs maintenance or replacement if it is locking up and making the engine have to work really hard to drive it. That could happen from it freezing up like Max said, or various other reasons. Or it could have nothing to do with the AC unit itself at all, IDK. Im not really an expert on the AC, but I did have that experience with finding out the AC starts to blow hot due to engine overheating. Other possible things to check would be the thermostat that controls the cooling system in the car, broken or cracked hoses in the cooling system, and other things in that area.
When was the last time you had your cooling system flushed and fluids replaced? (Not AC service, but the actual cooling system of the car)

[TOMatBMR]

First things first, perform a cooling system pressure test and check to ensure the fans are operating as designed. The secondary fan should kick on when the AC is turned on due to the increased load on the engine.