07 Ram 1500 weak A/C at idle

Hey guys,
My 2007 Ram 1500 has great A/C at cruising speeds of 20 mph and up, but sitting in traffic at signs or signals it starts blowing warm.
163,000 miles and I've never had the A/C serviced. I do all my own stuff on the classics except alignment and machine work, but I am not as familiar with A/C stuff .
I saw a TV commercial where a guy had a kit that tapped into the schrader valve in the aluminum line with a hose, valve and a cannister of refrigerant, but I wanted to get some advice here about it. Thanks, Greg

make sure the condenser fan (electric) on the driver side is running when AC is on. If not it is most likely the motor.

Verify by putting 12volts and ground directly to the motor connector. It should spin very fast (becareful). If not its a bad motor.

JM

Sorta funny story...
I looked at the fan and it seemed okay. The truck was idling with the A/C on, but the fan was still.I wiggled the wires... nothing. I spun the fan motor by flicking the blades. It spun slowly a bit, but that was it. I smacked the back of the fan motor and it came to life! Now I have to smack it each time I restart the truck.
The funny part?
AFTER I smacked the fan motor, I saw a buddy walking into the 7-11. He was glad to see me and threw out his hand. I tried to tell him I had dirty hands, but he grabbed my hand before i could get it out...He smiled and went into the 7-11. I got into the truck and looked back as he was wiping his hand on his pants.