under dash heater,A/C unit

[fireguywtc]

You might have a heater core issue. You wont regret removing the block from the "fresh air" intake side of the HVAC unit. That is the only way to get air into the heater side. Even though the factory AC is one unit, the heat and the AC are completely separate and blow into a common plenum. The AC is designed to only pull air from the inside through the evaporator (that's the part you can see in front). The heater is designed to get air from the fresh air side only.

Just old school technology.

[Cbumpus9398]

I assume the unit will need to be removed to change the core? That seems like a pretty good chore. Wouldn't I have a leak if the core was bad?

[fordman]

Getting to the heater core is a longer job than most. Its not hard. But you do have to take it apart in about 3 pieses. Or stages. I think.

It may be you could have additional blockage in there someplace.
The worse thing i dealt with was putting the drain hose back in while i had to hold the box in mid air sort of.

[Cbumpus9398]

I bought this truck last summer to restore with my son. We bought it from the original owner's grandson. I thought he told me before we left with the truck on the trailer that he had the heater core changed not long before. I can't even see the heater core. I guess it's behind the evaporator coil. When I touch the heater hoses under the hood and as they are under the unit, they become very hot. Almost too hot to hold for more than 3-4 seconds.

BTW-I piped the heater hoses through the base plate under the carburetor. I couldn't have gotten that wrong, could I? I did use a diagram to pipe that.

[fordman]

I dont think that could make it have less heat. Thats just a carb deicer spacer. Maybe the person who replaced the core did something wrong when they put the core in.

[Cbumpus9398]

Only one way to find out,uh? Take it out? Where is it? Behind the evaporator coil that you can see through the front?

[fordman]

Yes. And you may find the problem before you get to it.

[Cbumpus9398]

Ok, I have been working on the truck this afternoon and I have another question. While the truck is running, heater and defrost on. The air flow does seem to have gotten better since I took out the paper from the fresh air inlet but I noticed the glass all around the cab began to fog in an idle. There was no reason for it to fog, I wasn't even sitting in the truck to cause the fog. I wiped with my finger, then a towel. It appeared to have a film on the glass. I specifically cleaned the glass just a week ago. I have heard that could be the cause from a failed or failing heater core. Do you know?

[sargentrs]

Basic function of the heater and the A/C. There are two hoses from the water pump. One is an incoming (inlet) and the other is an outgoing (outlet). On the inlet hose is a water valve that opens (and lets in) or closes and (shuts off) the flow of water to the heater core. Once the engine is warm and the thermostat opens, hot water flows from the inlet hose, through the heater core, back out the outlet hose and back to the water pump. The "Heat-Cool" lever on your controls has a cable that moves the lever on the water valve to allow or close off the flow of water through the heater core. The heater core only gets as hot as the water running through it. Now on the air flow. The blower fan is a squirrel cage fan that spins based on which position the fan speed lever is in. Air is sucked in through the center and spins out around the circumference creating a vacuum in the box. The fan can only blow out as much air as is sucked in. The fan sits in a baffled pocket in the heater box with a damper flap that opens and closes based on whether you control is in the heat or defrost position (see photo). As you can see, the only place the air can be blown from the circumference of the fan is in whichever direction that flapper is pointing. Open, it goes out the floor duct in the cab, closed, it goes up through the defrost ducts. Halfway, the flow of air is split in both directions. That fan can only blow as much air as comes in through the center. With the fan mounted in the box and the heater box mounted to the firewall, how much air can be sucked through the center? Guess what, not a whole lot. Where's the warmed up heater core? At the end of the box (see photo). So the only warmed air you sucking in and trying to heat/defrost your truck with is what is captured in the heater box. Not much. Here's where the fresh air vent comes in. With the vent capped off like you had, no other air can be pulled through the heater core so you're strictly working with the air in the box. With the vent opened up, now you have a source of air that the fan's vacuum can pull in and create additional air flow, like sucking on a straw with the finger over the end and then letting go. The outside air is pulled across the heater core, warming it up, pulled into the fan and blown through the ducts. Since the fresh air vent is pulling air from around the cowl and in through the cowl vent in front of your windshield, the faster you go, the more air gets pulled in, the more air flow you have across the core. The down side of that is that the faster the air flows, the less time it has to warm up as it's pulled across the heater core. If the gaskets on the flapper are shot, the air goes wherever it feels like. If your defrost ducts are shot, the air gets spread around under the dash board. If your water valve is not opening and closing, no hot water is getting to the heater core so you're sucking cold air, or it's stuck open and you get hot water through the core in the heat of summer. If you're control cables are not functioning well, the flapper doesn't open and close, directing the air. A similar principle applies to the air conditioning part. Difference core, different fluid, similar controls, similar operation. More flappers, more choices for direction, mixing of hot or cold air, etc. Hope this clarifies the possible issues you're encountering. Here's a write up on when I rebuilt my stock heater box (I didn't have AC). Maybe it'll help you picture what's going on. http://www.fordification.com/forum/view ... hp?t=73960

[fordman]

Can you smell antifreeze in the cab. Something else i am thinking. But probably isnt. That the blower wheel is loose. And barely spins. So when the truck isnt mocing less air is being blown through coils.

[sargentrs]

Either that or your heater core is leaking coolant into the heater box and the fan is sucking up the vapor and spraying it on the windshield through your defroster ducts.

[Cbumpus9398]

Thanks guys. The fan seems to be turning fine. It appears to be noisy. I can't smell antifreeze. It's just that when I wiped the glass it didn't appear to be water (fog) it appeared to be a film. It took a hard wipe with a towel several times to clear. Then, after about 5 minutes it started coming back. I wiped with my fingers and then rubbed them together and it felt thin oily (slick). I guess I'm gonna need to remove it from the truck. Can you guys help with the removal of the unit? I don't want to break anything. I know it'll be tough, but it sounds like that's what coming?

[sargentrs]

I do believe that film you're feeling on your windshield is coming from a heater core leak. I've seen it before. I don't actually have an A/C unit mounted in my truck but I will be adding one and have it in the basement. Read through this thread http://www.fordification.com/tech/factory-AC.htm It mostly refers to installing one but does show the location of the bolts that hold it in place. Might be some help. The toughest part is going to be the control cables and you can probably take those loose once you have it hanging loosely from the firewall so you can get to the cable levers on the box.

[fordman]

Disconnect battery. Drain coolant. Remove heater hoses. Put bucket under hoses to catch coolant coming out of heater core. Remove three nuts from firewall around heater hose area.
Remove bolt near center hump under edge of dash. Unbolt fresh air boot. Lift upwards and outward to reach drain hose. It either just sticks through floor or has hose clamp on it. After its free continue with the same action dropping it down to the floor. You will also want to pich defrost duct rubber at base to remove them from the unit. Before dropping it down. After its down unplug electrical plug and heater cintrol cables. It should be loose and ready to come out of truck. You may have to remove glove box liner to get to plug and or cables. I dont remember when to remove ac hoses from the box. Maybe from glove box. Oh dont forget to drain ac system of refridgerant.

[Cbumpus9398]

Great thanks but the refrigerant is the issue. I don't have a vacuum for this. The a/c still works. I hate to mess it up. Any advice?