I own a 1998 F150 v-8 and I love it, but... When it's cold (winter time) the heater won't blow hot and when it's hot (summer time or anytime in TX) it won't blow cold. I thought I could trick it, like the ghost in the dash was stupid and I could make it think I really wanted cold air when I wanted heat by running the heater in the summer and vise verse... nope. In addition to this phenomenon the a/c will on occasion take pity and blow cold until I gun it, or hit a pot hole and then 'pop' sounding like a vent slamming shut, then it's 120 degrees in the cab and summertime outside of the cab. Same rules apply in the winter with the heater. When it does behave, the a/c and heat work beautifully. The compressor continues to spin after the pop sound so assuming what I've read to be correct, there isn't a need for freon. I've read temp blend door, broken actuator pin, I've read the pop/slamming of vent sound is a vacuum leak. Details of HVAC system leak included air reverting to defrost or floor vents which until today hadn't occurred. Kind of freaked me out, expected the Sahara to blow through vents, but no, the air remained the same temp, but wasn't flowing through dash vents. Is my truck possessed, to I need a catholic priest to do an exorcism? Help me survive this summer in Texas, I can deal with winter, I just brought a blanket with me and prayed I wouldn't need the defrost. Any help, or suggestions would be much appreciated.