Well i have an interesting problem, its getting cold out and i have no heat. i have searched other threads and cant seem to come up with a solution. Heres the deal. I have power and the fan runs at all the different speeds, coolant level is full, and is pressureising (new radiator cap). Before i replaced the cap the truck was at temp and i undid a heater hose, at the firewall, nothing came out until i lowered it below radiator level. once the truck reaches temp, about where the L is in normal on the gage (after watching it go to H and returning to L) i would turn the heat on. i have little heat on the 2nd setting then it goes away and blows cold. on the high setting, i have no heat, just cold air. i am at a loss. All the hoses are in good condition and i can see that the thermostat is working, what else could it be? The system does pressurize. any and all help would be helpful.\

Thanks

79 f100 302 auto ac but not hooked up. no vacuum valve that i can see any where.

 

Water pump possibly? Did you disconnect both hoses and check for flow? While your truck is running, one hose should dump water out pretty fast. What motor do you have by the way. THe cooling system is different on a few models.

 

Check your 30 year old heater core for restricted flow. Could be partially or completly plugged. If you have AC, check to see if you are getting vaccum to the controls and that the doors in the heater box are working.

 

well it has the 302, i havent pulled a heater hose while running.. it does not have any vacuum to switch the ac, i believe it to be dealer installed and not factory.

 

I had a similar problem on my 1967 F250 and on my 1977 F150. In both cases, it was a clogged heater core. I removed both heater hoses from the heater core. Then, I hooked a garden hose up to on side of the core and turned on the water. Next, I removed the hose and connected it to the other connector and turned the water on again. In both cases, a whole bunch of crud was rinsed out of the core and the heat worked fine after that.

 

That's the dealer installed a/c alright

 

"feel the hoses for hot water moving after starting it up cold" -Alvin

Ron's plan sounds like a good one to me. :)
But be careful with the pressure, be patient.

cooling system = 15psi
garden hose = 40 to 80psi

After getting your heater working ;) ...move your horn to the outside of the
bulkhead. BTDT in early '75, also bought a used "hi" to go with the original.

I inherited a '91 F150 and moved its horns too.

I don't ever blow my horn in "righteous indignation".
If you do... leave it there or disconnect it even? ;)

Alvin in AZ

 

Like Alvin said, feel the heater hoses. If one is hot and the other a lot cooler that the heater core is plugged.

 

thank you all!!!! I disconnected the heater hose ( one from the firewall and the other from the block) put a hose on the end of the heater hose (one at the block) and pushed water through, then i switched ends and watched black crap come out of the heater core, then grey, then after about 5 minutes, clear. Now i have heat!! Just in time because it will be down to 20 tonight, i know some of you have already had freezing temps, but it still suck with no heat in your truck. Thanks again and i hope to be a life long member and be able to contribute to anyone i can.

Jerry

79 f100 302 auto reg cab

 

After you flush any thing that involves the engine cooling system you should check the coolant protection level to ensure you don't have too much water in the cooling system.

 

To add to what was just said, normal antifreeze should be flushed every 1-2 years. If you are running dex cool, or other extended interval coolants, you have more time, but you still should flush. A cooling system with old coolant will still clog up your radiator, and heater core over time.

 

Keep in mind,your heater core may be in pretty poor shape from crud,and since its bypassed with a valve when your not using the heater,its probably older than the radiator. Its quite likely that your truck has had its radiator replaced at least once in its life,since it gets "used" every time you drive,while your heater core may sit idle for 6 months out of the year....... so dont be too shocked if the heater core goes out,but at least you got heat for now........

 

There is a vacuum valve that controls the heater. You just can't see it because it mounts to the backside of the heater control panel.

I see you've fixed the problem, mebbe someone else will benefit from the following.

D4AZ18495A .. Heater Water Control Valve (Motorcraft YG136)

Application: 1974/79 F100/350 / 1978/79 Bronco / 1971/96 passenger cars.

Still available from Ford, and why not? It's been a "best seller" for over 30 years.

MSRP: $28.72 / FTEpartsguy.com price: $17.23

This valve is a total piece of crap. When I say I prolly sold 5,000 of them, I'm not exaggerating!

The valve is black plastic and a sort of goldish colored steel, it's (supposed to be) spliced into the heater hose on the rear of the engine comparment, prolly more to the right side.

This valve is controlled by vacuum, when you slide the lever on the control panel to HEAT, this valve (is supposed to) open up, allowing water to flow.

This valve is notorious for rusting shut internally.

You can slide that lever till the Cubs win a World Series, nothing will happen.

btw: Your truck is equipped with Ford dealer installed A/C, but it's the Economy A/C, not the Deluxe A/C.

The Deluxe A/C has a huge bezel that sweeps across the dash from the instrument cluster to the right side end.

This bezel covers up the glove box, the kit came with another glove box that bolted to the bottom of the dash.

 

Bill wrote:
"This valve is a total piece of crap."
"When I say I prolly sold 5,000 of them, I'm not exaggerating!"

LOL :)

Got my pickup mid-Feb '75 and by fall of '76 the sucker was rusted shut. :)
Took it out, got it working, greased it up and it lasted another month or so.

"MSRP: $28.72 / FTEpartsguy.com price: $17.23"

"Johnson Motors" (no kidding;) in Safford wanted $40 and I put in a used
brass gate valve I already had. LOL :) (I'm from a farming family;)

Years and years later switched it to an engine-mounted ball-valve I found at
the hardware store, liked the looks of it, has a "big hole" in it compared to
it's size. :) ...notice the bulge in the middle?

http://www.panix.com/~alvinj/file12/bypass.jpg

Of course there's a couple problems with my setup...
Have to get out and open the valve after the engine is warmed up.
Have to remember to close the sucker when I park it overnight so
the engine can warm up quicker.

I've always tended to wear warmer clothes than most and just keep the
dangged things on when I get in a vehicle and so I don't need much heat
anyway.

Went to town yesterday in the '91 F150 and had to use the A/C most of
the time. LOL :) The sun shining in the window was trying to cook me at
one point. LOL :)

Lived in DC for a couple years otherwise I wouldn't know what it's like to
get "kind of cold" and just stay that way for months with no warm days.

But...
Would it really hurt anything to just let water run through the heater core
all winter without ever shutting it off?

Just how important is that quicker-warm-up anyway?

Alvin in AZ

 

I used to have a inline heater hose valve like you're talking about Alvin & just left it open all winter then closed it in the Spring, worked out just about right...didn't notice it didn't " get-warmer-quicker " at -20 in MO when I was a younger man .....never gets that cold here tho' ....