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My A/C is not blowing cold air until about 10-15 min into my drive most times. I can hear the compressor come on and then blows cold air. I replaced the compressor less than 1 year ago. Im thinking maybe its a relay or electrical problem and not the compressor. Once the compressor comes on it blows cold air for the duration on the car trip. any ideas would help thanks
 

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You might have a leak in the system, resulting in low refrigerant. It takes longer for it to build up pressure and therefore takes longer to start cooling the air. You may just need to get it charged up. Have them run a leak check while doing it to make sure you don't have a bad seal somewhere. An O-ring could have gotten crimped when your compressor was replaced. There could also be some blockage in the system or other component that's gone bad. Once you break the seal on a closed system like that you run the risk of allowing contaminants into the system. When the compressor was installed and everything was closed back up the entire system should have been pumped down and held in a vacuum for an extended period to pull out any moisture before charging it back up.
 

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Why not put a set of gauges on the system and find out what is really wrong with it . These systems have low pressure switches that prevent them from running low on refrigerant . Your compressor is engaging , so that's good . Is your suction line get cold immediately ? Systems actually get colder as they get low on refrigerant and will eventually freeze the evap coil . Thea is bad as the freon stays liquid and goes back to the compressor as liquid and ruins the compressor . Hence the low pressure switch . What kind of ambient temps are we talking ?
 

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Systems actually get colder as they get low on refrigerant and will eventually freeze the evap coil . Thea is bad as the freon stays liquid and goes back to the compressor as liquid and ruins the compressor . Hence the low pressure switch . What kind of ambient temps are we talking ?
I think you've got it backwards: Your R134a doesn't change to a liquid at low pressure, it becomes a gas. When the freon pressure is lowered, eventually it will not liquify in the condenser, and remains as a gas throughout the entire system. The basic concept of AC is the refrigerant changing from gas to liquid in the condenser, where it expels heat, then changing from liquid to gas at the evaporator, where it absorbs heat from the air, cooling it. The low pressure switch just prevents the compressor from running when there isn't enough refrigerant pressure to work.
 

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The low pressure switch prevents the system from getting to the scenario I mention . Any freon will condense to a liquid when the heat is removed . Most systems will have as sight glass after the condenser coil . When the system is low there will be liquid freon but it will be foamy . This is when the evap coil temp will drop to below freezing . I do air conditioning for a living and when a system is low the coil freezes and slugs liquid freon back to the compressor because there is no pressure drop in the evap coil as it has no air movement over it. I've pulled the doors off of units running low on gas and the coil is one huge frozen block of ice . By this time the compressor has usually overheated and stopped running . I'm pretty fimilar with the workings of an ac system . I'm EPA cert univercial . So I'm not real sure what you mean when you say I have it backwards ??
 

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Any freon will condense to a liquid when the heat is removed . Most systems will have as sight glass after the condenser coil . When the system is low there will be liquid freon but it will be foamy . This is when the evap coil temp will drop to below freezing . I do air conditioning for a living and when a system is low the coil freezes and slugs liquid freon back to the compressor because there is no pressure drop in the evap coil as it has no air movement over it.
Strictly speaking, gaseous freon will always liquify when heat is removed. But at ambient temperatures in the real world, there exists a low enough pressure that the gas will not liquify, and that is when your A/C won't get cold. As to the sight glass, its been a long time since VAG cars used those, but I remember them.

I'm not here to argue, and am not an A/C professional, but at one time was employed by Mazda to improve their A/C systems. I redesigned an evaporator layout precisely for the reason you mentioned; the core would freeze up and air flow would stop. In this case it was because air flow was stagnant in the lower part of the evaporator's case, and condensed water running down the fins would freeze, instead of draining out.
 
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