Printable View
guys my truck will not defrost. ever. i have the blower motor switch on, the heater cable pulled all the way out and still nothing, no hose blockage that i know of, no disconnections and i get no air pressure across the windshield. about 45 minutes into the ride, my passenger side develops a nice portal to look through. ummmm what happened? what'd i miss?
Is there any air coming out of the ducting?
if the fan is running look for air at other points. If no air at all look for a cloged heater core (mouse nest)
The stock defrosters blow very flat to the windshield only right above the openings which are partially restricted due to being recessed down in the windshield frame a bit. I have issues with defroster output when its really cold...below 0 and down...
Did you verify that the cable is fully moving the arm and that the plate inside the underdash box is fully moving from heat to defrost?
First, do you get heat? Maybe its closed off some at the heater core and you arent getting any heated air coming in....the blend air door in the underhood box would be the one to check there...make sure it is being fully opened.
Remember, just because the cable moves the arm on the outside of the unit does not mean that the door is opening and closing on the inside...or that it is moving through its full range...need to verify if it is truly doing what it is supposed to.
Also, it is possible that the fresh air intake is plugged...if you stand on the passenger side of the truck, the grill work on top, just behind the windshield, the cowl, is where the fresh air heater breathes in from. Leaves and debris can get in there and then get sucked into the opening to the fan thus restricting or completely blocking off airflow.
will check all these points. no air is moving within the cab.
Let us know what you find....no air movement means something is wrong...
is this going to require pulling the entire unit out to verify all working components?
Open the hood. Remove the 2 or 3 screws that hold the fan to the firewall. This will be right next to the passenger side hood hinge. You will probably have a bunch of leaves and junk in the fan housing itself. Make sure the fan is free and moves ok. Check under the cowl also for obstructions.
You can now look into the heater core housing. There should be a metal flap door. This flap directs the air either to the heater core or straight to the inside of the truck. Now is a good time to make sure your "Heat" cable actually does something.
If you still haven't found anything odd, then find a leaf blower or a shop vac that can blow air. Stick that into the heater core housing and turn it on. You should have air blowing inside the truck too. If you do, then the problem was with the fan or the junk you already pulled out. If you don't, then the next flapper is probbly the problem.
Go inside the passenger side of the truck. On the top of the heater ducting right next to the firewall is another cable operated flapper. This one controls how much air gets inside. Try moving it by hand. If it moves, move it so air enters the cab. If it doesn't move. Then that is your problem. There are 4 bolts that hold the inner ducting on. They have to be undone from under the hood. You will find it easier if not manditory to remove the heater core bolts at the same time. The two parts kind of hold each other on, but not completey. I don't have one here with me right now, but once you figure out the bolts, it will take about 10 minutes to remove both the heater core and the ducting from inside.
I had a cj7 with a motor (or fan) that spun the wrong way.....
cool. alot easier than i thought. thanks barrman!
ok figured it out: the damper at the blower was rusted in place bocking air. pb blaster took care of that issue. damper for defrost redirect within the cab duct-rusted in place. pb blaster took care of that issue. tried the cable. cable broke. new cable ordered. opened up the thermostat housing....umm....no thermostat-at all-missing, never reintalled...new thermostat ordered. HVAC work: done and done.
Good deal.
Yep. good deal....thanks for letting us know what all it was...helps for the next guy with trouble!!
it sure is nice when things are so simple.