Q: A.c blows cold air when stopped but after driving for a few mins it makes a hissing sound and blows hot air

asked by on July 24, 2017

We just charged the ac and it works great while at a stop it blows ice come air but I noticed while driving and higher rpms it starts making a hissing sound from the driver side vent and hot air starts to blow instead of cold but when I slow down and stop it starts cold again. What's the issue its very frustrating especially with a pregnant girlfriend!

My car has 94000 miles.
My car has a manual transmission.

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It could be that the evaporator is freezing up. If the air conditioner works TOO well, ice can form on the evaporator core. When that happens the AC will blow hot air until the ice melts. There is supposed to be a thermo switch that prevents that, but it could have failed. Another possibility is that the system is overcharged and when the engine speed picks up, the high pressure switch turns the system off. Either way, the system has to be diagnosed by somebody with the proper equipment. You can contact Your Mechanic to have a technician come out to your home or office to check out your air conditioner and recommend a solution

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