Heater is not coming on

Probably a problem with the controls (broken wire/cable) or the diverter/flap in the duct. Its stuck on cold. Find the diverter and look for what controls it. Make sure it moves or see why it wont. May have to remove glove box.

I've had the same problem, this hose (click the box) is a lot of times disconnected for what ever reason. Hooking it back into the nipple solved this same exact problem you're having. Well the click box thing didn't work. Look at the black vacuum "T" just to the right of the brake booster, the hose that goes over to the fender unhooked is the hose I'm talking about. Nipple is sticking outwards underneath where that hose is under the rusted metal flap.

There are two relay's in the under hood fuse box .Low beam & high beam relay's . The B+ voltage wire for the switch is orange with a black trace . Power is from fuse F26 7.5 amp ,location -central junction box , inside the passenger compartment . Do you know where this is ? This is B+ voltage for control of the relays . B+ voltage for the headlamps comes directly from the BATTERY . Do you know what a wiring diagram is ? Free wiring diagrams here http://www.bbbind.com/free_tsb.html Enter vehicle info. Year , make , model an engine size . Under system click on lighting ,then under subsystem click on daytime running lamps . Click the search button then the blue links .

look under the left side of vehicle (RHD vehicles)right side of vehicle (LHD) in centre of car for heater cable going to heater case control levers on side of case can see it better if glove box removed. make sure cable is clipped in its retainer clip properly/ remove and adjust cable while control lever is over all the way and flap controls on case are fully over in that same direction as cable moved when putting control lever all the way over and clip into retainer. if cable doesnt move when moving control lever its probably come out of clip other end of cable in behind control lever or snapped the usual is glove box/heater case side first second is cable snapping behind control levers.

Two things come to mind one the flap on the inside of the air duct is not switching over to allow heat to come through. Second your heater core could have a blockage. Go under the hood find both heater hoses run your truck till it reaches normal operating temp then feel both heater hoses one at a time. If one feels very hot and the other feels cold or even luke warm you have a blockage.If they both feel hot then look into the duct works under the dash. There should be a valve that switches the door between your heater duct and your ac duct that may not be operating properly. Some valves are vacume actuated so look for a broken vacume line.

check heater flap cable ajustment to make sure flap is shutting off so no air from heater core is going into evaporator common problem.
cable moves or comes out of retainer clip remove glove box to see

this sounds like the recirculation door in the heater box is broken and this is a difficult and can be an expensive repair as the dash has to be removed for access. a quick check for this is if you release the glove box and let it hang you will see the heater box if you reach up to the left top you will feel a grid and the recirc flap is housed there you can operate the blower and hot and cold and see if flap moves

remove the trim panel below the glove box and you will see the blower motor,just to the left of it you will see a 4 wire connector plugged into the case. This is the blower motor resistor,this is what you need to replace.

normally if you take the two hoses coming out from the heater core you will find the heater control valve if it is under the hood and sometime they are in the truck on the passenger side down under the glove box

There is a fuse panel under the dash on the driver's side and the maxi-fuse box is under the hood on the driver's side. If the fuses are good, it is probably the blower fan which is located under the dash on the passenger's side. (Behind the glove box.)