Duke2U

I live in AZ and during summer I leave work when its 110+ (you can imagine how hot the cab would be). When I start driving, AC works fine, but does take time to cool down the cab (I wish it did so faster, but I suspect this is the downside to having a king cab).

The problem occurs when I restart the truck after having reached operating temp (e.g. stopping at the store to pick something up). For the first few seconds, the AC blows hot humid air, and seems to take quite a while (4-5 min) before acting normally again.

Could this be a problem with the heater control valve? When the truck is turned off, does the vacuum subside and allow it to open whereby hot coolent entires the heater core? Should the vacuum reservoir hold pressure for some period of time and its not doing so? This isn't a killer problem, more of a annoyance I'd like to understand better.

wwb

When you shut the truck off, you have a huge chunk of iron that's well over 200 degrees sitting under an insulated hood.

After sitting a few minutes, it will heat up the entire heater/AC system.... even the firewall and the cab ducting. After you start the truck, it has to cool down all that material. Plus, the heat soak will raise the refrigerant pressure in the A/C sytem, and it will have to cool down some by running outside air and drop the pressure before the compressor will kick in. That's the warm, humid air you're getting. Once the compressor kicks in, it will cool almost instantly.

If it's a major nuisance, and you know that you're only going to leave it for a couple minutes, get a second key made so you can leave it running and lock it. If you're going to be gone for more than a couple minutes, as you said, it's not the end of the world.

papabear8233

When the engine is shut off the oil temp increases over 25 degrees above the coolant temp. There is an oil cooler in the vally on top of the engine.
When this happens the computer restrict fuel and shuts off AC till the oil return to the proper temp.
Leaving it run is the answer.