The air-conditioner on our GMC Yukon does not blow cold when stopped at a light or such. The fan still blows, but the air is not cold unless the Yukon is moving. Can this be fixed?

Have your cooling system pressure tested to find your leak.

I will assume the ac is still getting cold, just not blowing.
You wouldn't really know unless you pulled the panel and checked the lines.
Causes include the blower motor, resistor, fuse, or switch.

Could be a blend door problem under the dash.

check if the a/c fan is blowing if it is then change ur a/c condensor

Have more refridgerant added.

the most common problem here is a defective air temperature control blend door actuator, this is what moves the door that controls air flow across the heater core or the ac evaporator core, to replace this requires u remove the dash assembly.

first off make sure you have no blown fuse. but front blower motor may be bad. if it does not work in any speedyou can check for power at the wires going to the blower. under dash on passenger side

Check the magnetic clutch is engaged on front of a/c pump, have the motor running, a/c on and fan on high, if the centre hub is static the pump in not switched on, this can happen when the gas pressure gets low.

check you antifreeze level and make sure its full

Turn your AC off. Turn the car off Crank the car turn ac on drivers side to 60 passenger side to 90 press auto wait 1 minute turn AC off (very important) turn car off turn car back on switch driver's side 90 passenger 60 press auto wait one minute turn AC off( very important) turn car off turn car on AC 70 both sides press auto your ac should be blowing cold If not, you have an expensive problem