Why does my car only blow out cool air but not hot air

First of all, what year is your Patrol? They've been making them since 1951, so there have been a lot of changes since then and we can't give you a fully accurate answer without knowing which one you have.

That being said, off the top of my head here are some of the more common causes I know of.

• Blocked heater core
• Faulty mixing valve/controls
• Pinched heater hose
• Broken air baffle

Your heater works by running hot air through a small radiator, commonly known as the heater core, which heats the air and blows it into the car's passenger compartment. There's a valve in the heater hose that turns the flow of coolant off and on, letting more or less fluid through the heater core to adjust the temperature to hot, cold, or somewhere in between. Finally, there's usually an air baffle that directs the flow of air, either before or after the heater core (or both) to direct the air and switch between heat, vent and A/C (if equipped).

So what you have to do first is figure out where the problem is. You need coolant flowing through the heater core; the best way to be sure that's happening is to access the heater core itself, put your hand on it and see if it gets hot when you turn the controls to heat. It should, of course, cool off when you turn it to cool. On most cars it's not easy to get to the core, so that can be difficult to do depending on the year and model of your vehicle.

The above test also verifies that the control valve is working; it won't get cold/hot if that valve is stuck in one position. Again, you may have to get into the dash to find the valve and visually verify that the heat control dial/switch/lever physically moves it when you vary it. It could be electrical, a mechanical cable or run by vacuum.

Likewise, the air baffle that controls the source needs to physically move when you select different functions. Moving it to vent can bypass the heater core, in the heat position it goes through the core, and in the A/C position it may or may not also bypass the heater core, switching to the evaporator instead. These functions are all highly dependent on the heating/cooling system design and can vary widely between models. But in general there should be physical movement when the control is operated; if not it could be an issue with the controls, whether they're electrical, vacuum, or mechanical.

There could be more possibilities, but your comments seem to indicate that your car's general cooling system is probably operating, and the blower fan sounds like it is working since you said it blows air.

That's about the best we can do with regard to information since you haven't given us much of anything we can use to actually diagnose the problem. If you come back and add your vehicle information and any other troubleshooting you've done, we may be able to give you more specific answers.