Hello everyone, I have a 97 F150 Lariat Supercab with 252,000 miles with my first HVAC problem.

When the truck is first started, the A/C works just fine. Once you rev the engine, or start moving, there is a decent "THUNK" sound from the duct work, and the air temp switches from ice cold to very hot (98 air temperature in Alabama combined with 200 water temperature in heater core = melted steel). I am assuming that this sound is the Blend Door slamming to block the cold side and fully open to the hot side. Once the truck has been turned off and has sat for about 10 minutes it will go back to normal.

My question is... Is there something that can be done for this without having to remove the entire dash?

I have found the wonderful instructions here for replacing the core and blend door, and will go this route if required. But really don't want too as you only need heat here for about 40 mornings a year, and need A/C about 300 days a year. Also, I'm sure you noted the mileage and while I fully believe there is at least another 150,000 in the truck, I don't want to start doing too much to it at this point.

Thanks!
GaryC

 

Nope. At least nothing constuctive.

Well, perhaps you could bypass the heater core except when you need heat.....

 

Whereabouts in Alabama are you? If you want to take this job on, I'd be willing to help if you aren't too far away from me. We could get it knocked out in half a day or so.

 

Quintin,
I'm in Chilton County. 20 miles from the dead center of the state. And thanks for the offer, but I don't know if I'm going to fool with it yet or not as it doesn't get driven quite the daily mileage that it used to get. But if I decide to do it, and you're still willing, I'll let you know.

Being in the commercial air conditioning business, I have to wonder if it would be possible to take a Dremmel and cut a hole in the duct work and put some kind of manual rod on the blend door.???? I know it is the redneck way, but sure would beat the option. Any thoughts on that one?

Thanks,
GaryC

 

You could bypass the heater core altogether by taking the heater hoses off from the back of the core under the hood (passenger side firewall) put a splicing tube in there and reattaching the clamps. I think you can get the splicers from any autoparts store , you just nned to know the hose size, just be sure to reconnect them during the winter.

 

Could I get the "wonderful instructions here" for replacing the core and blend door.

thanks

mellis

 

where can I get the repair instructions for replacing the blend door for a 1999 navigator.

thanks

 

Search this forum, cross-referencing "blend door" with my user name. I did a quick and dirty write up with some pictures of the who's, why's, and how's of replacing the blend door.