My air conditioning works perfectly on the freeway, but under stop and go conditions in town it stops working and blows warm air at low speeds or when I'm idling. Is it the AC belt or the compressor or . . . ?

AMBER
the car needs service
the throttle by wire is failing.

common this.

https://www.impalaforums.com/threads/p2122-code-accelerator-or-throttle-body.1818978/

DTC P2122: Accelerator Pedal Position (APP) Sensor 1 Circuit Low Voltage


the means the DEVICE under right foot is bad./
electronic throttle pedal device.

any shop in town can repair this.
no need for dealers.

I think you have a similar problem to mine. At highway speeds is when it happens. And it is not blazing hot? Right?
Your evaporator is freezing up - as this happens the ice surrounding it prevents the flow of air over the evaporator coils and the result is warm air coming out of the registers. If I turn off the AC for about ten minutes and let unit melt the cold air comes back. This does not occur in stop and go driving.
I combat it by either running the fan at a higher than normal setting to increase air flow over the evaporator and then turning off when it gets too cold, OR using the air control to allow warmer outside air to enter into unit at highway speeds to prevent freezing up.
Newer cars have more sophisticated sensors and controls to prevent this but some older vehicles are subject to this anomaly.
Since it works fine under normal conditions I have not messed around with the freon level in system. If you release a tad of refrigerant the low pressure switch will shut off the compressor sooner and help minimize ice buildup. Good luck.

you need a blower motor resistor to get all the speeds again.

Check to see if the radiator fan is coming on & the AC fan comes on when the AC is turned on. AC Freon may be low too.

CHECK THE THERMOSTAT. THERMOSTAT IS THE ONE THAT SENSE THE ENGINE TEMPERATURE AND TURNS ON COOLING FAN WHEN THE ENGINE IS HOT.

First things first.....You must have the air conditioning system hooked up to an a/c system machine and then checked for leaks and also read low and high side pressures. If there are leaks then low Freon (R134a) content and low refrigerant oil can cause the a/c system to not engage the a/c compressor which basically means you will not have proper defrost functionality nor regular air conditioning. Most shops, when working with your air conditioning, will install air conditioning dye to assist them in locating leaks and is the first step in diagnosing all a/c systems. Post the findings after thw

several things could be wrong such as low freon or a bad vacuum line or switch controlling the door to open for a/c

Is any air coming out at all?

If warm air is being blown out, then your refrigerant level is probably low. The car is fitted with a safety cut off, to stop the air conditioning system working if the refrigerant (R134a) level is low.

This cut off only effects the air conditioning, the blower would still function normally.

You may have a low charge of freon, most likely about 10 ounces, as far as the musty smell that is mold from the inside of the AC air box, they make various chemical tratments to cure this issue, but once the smell is there it can be diofficult to kill the mold that causes it.

One suggestion. Have you checked the fuses ?

I would check the AC or blower fuse to start with. If you have the drivers manual it will show you where the fuse box is. Typically there are at least two boxes to check. One in the Engine compartment and one in the passenger cabin.

Look inside the lid of the fuse box to see which fuse may apply to the AC circuits or the blower and check to see if they are blow. the metal link between the two posts that plug in. If the link is missing you need to replace the fuse with one of the same rating. Make sure you know where you took the fuse out from and put it back in the same slot if its good. Check all the main fuses if possible to see if any have blown and replace if they have.