84 C10 Heater...

[yellomalibu]

Prior to a trip "up north" like I just took to go hiking in the mountains - this time in southern Virginia - I like to change out my usual 160 thermostat to a 180 thermostat so the heater works better. (the 160 keeps the underhood temps down so the AC works better in the summers down here and allows for a few more degrees of timing before detonation)

Driving around with the outside temps in the 40's, it just wasn't doing much for me. When I had to kick on the AC compressor to de-fog the windshield, of course, it blew colder, even with the heat control lever all the way over to "hot". Understandable, since the defogger/ defroster engages the AC it should be colder air... but it wasn't warm at all. It seems to bring the most heat in the cab when the system is turned to "off" and the heat control lever is all the way over to hot. The faster the fan blows, seems to blow colder and colder.
The heater hoses shouldn't be clogged, since I replaced them a few years ago.
-I did install an inline shut off valve on a heater hose 3 or 4 years ago, also to help the AC blow colder - but I opened it and left it open because it didn't make a difference in AC temp. Could it be restrictive of the hot coolant or clogging up over time causing a restriction?
-Do old heater cores get clogged with leaves and debris inside the heater box, greatly decreasing their effectiveness?
-Do they get clogged inside? I've only heard of heater cores being replaced when they start leaking.
-Is it likely a flapper door issue?
-Is there something common I need to look for, or is it just "those old trucks don't have good heaters"?

Any ideas based from experience with these trucks?

[STINEY]

I played with several different plumbing option used by GM at that time when I pieced my '81 1/2 ton Chevy van (all in the search for more heat)

I also played with the slower coolant flow vs faster coolant flow theory, and undebatably faster flow is better for more heat in the cabin.

I'll get my layout for you tomorrow.

That's the same parts as your truck, as GM used truck parts bin to build vans from. And the van cabin is vastly larger than a truck, so don't believe anyone if they tell you it's just the way they were.

[Barry Donovan]

I remember them.
there is a cold route and a hot one for the entrance hose.
the 70s-80s, we all had awesome heaters.
I can't remember where we tapped from to go to box..
right rear passenger head? I think there was a swap to thermistor and heater hose or something.
very hot. Couldn't use normal hoses.. had to be braided etc etc.

in fact, those got so hot, a certain type of ice storm could crack the windshield by kicking on defroster.

where is the feed for the core coming from now?
the real hot entrance is also where you may have gotten the valve idea. Even mainers used one.

[squirrel]

they work good when they're working right. Could be lots of different things, and you made a pretty good list of the likely candidates. Disconnect hoses, see if water will flow through the core like it should. The other stuff probably requires taking things apart...I seem to recall it's not too bad, we did the core in the 87 suburban when I got it because it was leaking. There are plenty of duct/door/control things to get messed up.

[Deaf Bob]

77 flatbed takes forever to get heat out of it, new core..
90 Suburban factory air works great!
85 GMC also factory air but a diesel converted to gas works pretty decent altho slow
Was told I got the hoses to the core backwards in the flatbed, Have not switched as I rarely use in really cold weather (working outside hauling stuff)

[JamesMayberryIII]

on defrost, the ac compressor cycles... nothing more..( only does this to keep it oiled and not seize) if you are getting cooler air when on defrost.. the flapper door is not closing..
check that all the doors open and close completely and seal..

[squirrel]

defrost runs the ac to dehumidify the air. It cycles quickly, because the evaporator stays pretty cold because you don't have the flapper door in the "cold" position, it's in the "hot" position. something about how CCOT ac systems work.

[Deaf Bob]

My kid's Toyota has a bad core, before he stopped driving it ( great deal on a Crown Vic) he kept the windws clear with the ac.. Core was bypassed

[Dan Barlow]

You can check if the heater core is clogged by getting the truck up to operating temperature with the heater on . Check to see it the two hoses to / from the heater core are about the same temperature. If not it is clogged . If clogged take the hose loose and drain it . Then try to back flush it with a garden hose . If that doesn't unclog it extend the hose so you can get them above the core then fill both hoses with CLR or something like that. Let it sit a few hours . Try back flushing again . If that doesn't work , your bying a new one .

[yellomalibu]

It's been an issue since I've had rhe truck, but now my passenger floorboard is wet with antifreeze, so I'll find out soon if the box is full of leaves, and maybe I'll be able to tell if flapper doors are closing/ opening all the way.

[yellomalibu]

...and I did flush it with the water hose so it would stop draining antifreeze into the cab. Nasty black stuff came out for a while before it started clearing up.

[Dan Barlow]

If you were getting antifreeze in the floor then I'd think its time for a new heater core .

[yellomalibu]

If you were getting antifreeze in the floor then I'd think its time for a new heater core .

Yep. I called the parts store, and they have one in stock. I'll pick it up today. I'll make sure they don't list a different p/n for the high hump trucks before taking everything apart.

I watched a couple youtube videos on how to do it, and it looks pretty straight forward.

I think I will play with the cable adjustments when putting it back together (and maybe as I'm taking it apart) because the lever for the cold <--> hot adjustment seems out of adjustment. When I slide it to the left for "cold", you can hear the door thump shut and the lever stops with approximately 1/3 more distance to go. I can force it over the rest of the way, but it's not closing the door any more, and feels like it's just bending a bracket or binding up something. So, if I adjust it so that the door thumps closed all the way to the left in the "cold" location, perhaps that means the heater door will open more when the lever is all the way to the right.

Perhaps I'll get about 6 feet of various sizes of vacuum hose, so I can replace any dry rotted hoses while I'm at it.

[Beagle]

Looks pretty straight forward... errr.... is that an A/C truck? I wanted to shoot mine (86) by the time I was done (think I did that in 88). There seem to be a lot of guys who say to leave the bottom screw out. Good luck man, you seem more patient than I was at 21, should be a piece of cake. I'm sending positive energy your way.

[Russell]

When I put the hvac from the 89 into the 87 mustang, I put a new heater core in it. Every were I read said to get a high quality brass core that the cheap aluminum ones did not last long. I also added a flow restrictor I made from an old brass plug, ford added them in the later cars to reduce the pressure on the core. I am more worried about the life span of the $80 core than heat temp.