AC expansion valve

question: Can a malfunctioning AC expansion valve cut the cold air off and let warm air in? The car (Saab) is cool then shuts off after a minute or so, or just brings in warm air to begin with. The car has had AC recharged and the Dealer/mechanic doesn't seem to be able to fix problem. He also says this will cost $1000. The retail part is $98. Just want to make sure this is the problem.

 

If the txv is bad and not letting any refrigerant through the evap, the air temp will be ambiant, so to answer your question, yes.

 

Before you replace the expansion valve, you should hook a manifold guage set up to your car and monitor the pressures as it is happening.

Your car could also be low on refrigerant. That would produce similar results. It has enough for the compressor to turn on and start compressing the refrigerant, but then the low side pressure drops too low (while you high side pressure is fine) and the saftey switch cuts off your compressor and you get ambient air blowing in.

If your expansion valve is bad, your High side pressures will probably be too high.

Your car could also have moisture in the system, causing excessive high side pressures, and then the saftey switch cuts off your compressor and you get ambient air blowing in.

When you get "warm air" blowing in is it warm air or ambient air? Air hotter than ambient temperature could indicate a problem with you blend door.

When you get "warm air" blowing in is your compressor clutch still engauged?

What makes you think its the expansion valve?