Heats for the first 3 minutes or so and then just drys cold air.. is it a thermostate problem?

THERMOSTATE SIGNAL SHOWING OVER HEATING AND NOT RUNNING NORMAL ,HENCE OVER HEATING TRY CLEANING MAY HAVE DUST OR IT COULD BE THERASTSATE TO CONTROL AIR TO COOL

Does it restart after it cools down? If so your motor may be overheating and shutting down.

check which of the fans is running it could be the one for the airconditioning thats turning and that would explain why it over heats around town because there is no cold air to cool it and there is when you are driving on long trips

a stuck or broken thermostate would do that if the moter temp takes a really long time to warm up the thermostate is stuck open and needs to be replaced if the moter warms up to fast or over heats the thermostate is stuck shut and needs to be repalced. the heater core its self could be plugged and may be fixed by back flushing with water if you do it your self flushit seperate from the moter to prevent what ever may have plugged it from re-entering it.

CHECK THERMOSTATE WIRING.
HEAT (h) AND COLD (C) WIRING MIGHT BE CROSSED.

Dry is a dehumidifier option. There is a heating element in the unit to heat the cold air back up. The cold evaporator coil causes the moisture in the air to condense on the coil (this is why the AC leaks water) and the air coming out of the vents will be cold. If you are not wanting to lower the temperature in the room but want to take out the moisture then use DRY. All ACs take the moisture out of the air when they are on COOL. So, COOL drys the air and makes it cold. DRY drys the air but warms it back up before sending it out the vents.

FP is the code for frost or freeze protection. The unit will automatically do this periodically to prevent any damage caused by low temperatures although it should not be running as frequently as every five minutes. If the outside temperature is not low then it could either be a problem with the exterior thermistor (not the one you see from inside your room) or the control board could be on its way out.

Sounds like a thermostat problem to start with. Follow the top rad. hose to the engine. You will have to bleed the system of air after.

first make sure you have the right a mount of anti-freeze in it first and there is no air bubbles in the systems but to change the thermostate follow the upper radiator back to the engine and for the most part it only has 3-screws holding it make sure the engine is cool and that way you do not lose all of your anti-freeze and put the new thermostate in the same way the old one was.