In the spring of ‘92 I bought a LD K2500 ECSB with the 5.7 and NV3500 and 9k on the odometer ( it was the dealer’s personal/demo truck). In June during the first heat wave of the season I was in town doing errands and making numerous stops. It seemed like it was taking forever to cool the cab down between stops. I stopped in at a friends shop to see if he could take a gander at it. He reached in to his toolbox and handed me an A/C thermometer and said “stick it in the center vent and run the A/C on max, should be 40-44 degrees.
After driving around for 15 minutes the thermometer read 42 degrees.
I think the design of the GMT 400 dash and ducts lend themselves to getting really hot in the sun, and it takes them a while to cool down, and on a hot, sun beating down kind of day, the A/C is working to cool the dash and duct work in addition to the cabin.
The heaters in my 96 and 97 K1500’s will give a guy heatstroke in 20 below weather.
My 96 and 02 Express/Savana vans A/C will give a guy an ice cream headache, but the heaters suck……..