NO heat!!! thermostat?

[NeXtras]

doesnt jump around... it eiter works or doesnt when i start.. its NEVER been straight up and down

 

[tomtoc]

my temp gauge gas never worked the right way.. sporatic if anything.. dunno how to check blend door

sporadic like electrical jumping or sporadic like slowish movement when the engine would get hot/cold (air bubble)

EDIT: nevermind

 

[Old_Paint]

Temp sending unit for gauge is single wire unit, normally pretty close to the ECT (to ECM for timing/enrichment) which is two wires. Sometimes, corrosion will form in the threads of the sending unit, and it will get wonky, but 10 times outta 9, the sending unit is bad. Put a new one in for about $12. Seal the threads with a paste type sealer. Do NOT use thread tape, because if that stuff shreds, it'll clog at least one tube in the radiator, or perhaps one in the heater core. Since its on the discharge side of the pump, it will go to the core first. Get a piece wrapped in the seal of the pump, and that seal will be toast.

Thermostat, yeah, they can stick open too, but more often than not, they stick closed, resulting in an overheating engine. I'm not saying yours hasn't because I've had one stick open. And yes, the guage won't come off the bottom if the t-stat ain't working. Coolant temp's gotta get to at least 160 deg before the ECM will switch to closed loop control, so you'd see a cold engine problem (stuck open t-stat) on your fuel gauge too. That thing will drink fuel when it's running open loop.

If it takes more than 4-5 miles to get to operating temperature, that would surprise me, if you also have the 5.0. Dunno how the 5.8 or 4.9 behave, though. Even with a manual tranny, mine's at normal temp within a couple miles after I start, and I'm hunting some cooler air outta those vents.

On to the cab heat problem, my guess would be plugged core if there's no heat at all from the vents, yet the radiator and top hose are warm/hot. If it's just warm air (not HOT) coming out of the vents, then probably blend door. (Did you lose your favorite tire pressure gauge?) If you're not moving, i.e. no wind blowing past the truck, and there is no outside air coming in, it would eventually warm the cab, mind you not very fast. Outside air is used on the MAX A/C and VENT settings, and MAX A/C also bypasses one more resistor in the blower circuit to let the fan REALLY hump. VENT position opens outside air door, then blend door is controlled by temperature setting knob. I run my heat on VENT setting most of the time until the cab gets toasty warm, then put it down on the floor to maintain the heat and warm my feet. I've never been able to stay in the cab with mine on full heat after the temp gauge first starts moving.

BTW, mine's a '92 model that I bought used with 16 miles (no, not 16K, but 16). Coolant's been changed exactly twice in the life of the truck, and the ONLY hose that's been replaced is one of the little ones for throttle body de-icing. Heater core has NEVER given a problem, and will run you outta that cab within 10 minutes after starting the engine. I did replace the t-stat when I was having some issues with fuel economy. Factory issue is 187 degrees F. I suggest putting the same back.

 

[subford]

Sorry I could not let this part go by.

(Did you lose your favorite tire pressure gauge?).

What does the tire gauge have to do with it?

If you're not moving, i.e. no wind blowing past the truck, and there is no outside air coming in,

Not true, when on heat you are only taking in outside air.

Outside air is used on the MAX A/C

The other way around, no outside air on MAX A/C.

and MAX A/C also bypasses one more resistor in the blower circuit to let the fan REALLY hump.

Not true, electrically the it is the same.

Factory issue is 187 degrees F. I suggest putting the same back.

The Factory issue is 195 degrees F.

 

[Old_Paint]

What does the tire gauge have to do with it?

Fallen down in the blend door, perhaps? As would most anything thrown up on the dash.

Not true, when on heat you are only taking in outside air.

Not according to the owner's manual, if I remember what I've read correctly. But, you have the EVTM, so the O/M may be wrong. Normal A/C, Heat, bi-level, and defrost are all supposed to recirculate cab air. But, I'll take your word for it. I haven't gotten under the dash and watched the cables operate, so I can't argue this one intelligently. It wouldn't be the first time a manufacturer's owner's manual contradicted the shop manual.

The other way around, no outside air on MAX A/C.

See above regarding heat. O/M says outside air on Max A/C and Vent, recirc on norm. Compressor does not run on vent, obviously, only on Defrost (cyclical) for dehumidification of air diverted to the windshield, Norm A/C, and Max A/C. The compressor is either on or off, and does not vary it's output, so the only ways to get colder air is slow air flow down and push colder air across the E-coil. Max A/C moves air fast to lower temperature quickly, and does not chill the air as well as Normal A/C (because of increased air flow and less efficient heat exchange.) Once cooled enough, most turn the A/C back to Norm, and reduce fan speed to decrease fan noise. Put a thermometer in the vent, and watch the temperature of the air coming out. You'll find it's much colder air on lower fan speeds. The difference in the feel is the volume of air, not the temperature. Obviously, moving the air slower takes longer to cool a given quantity of air. Owning a black truck in the humid South will teach you a lot about opening the windows a bit and turning to Max A/C to cool the cab quicker to a tolerable temperature, then switching to Normal and closing the windows to further dehumidifying. 85 degrees at 20% humidity is a LOT cooler than 90 degrees at 90% humidity. Pulling in outside air totally defeats dehumidification.

Not true, electrically the it is the same.

Care to explain the difference in fan speed on Max A/C? The ONLY way to speed up a permanent magnet motor (the fan) is to increase voltage across the armature. Dunno 'bout your truck, but the fan speed almost doubles when switching to Max from Normal A/C (or anything else for that matter) in my truck, and the fan sounds like a booster stage for a 747 jet engine. Max A/C is the only setting this occurs on. All fan speeds are faster on Max A/C in my truck. Not that the fan runs too slow on other selections, nor does it have any problems that I know about other than being the original fan and possibly caked with dust bunnies. I get what I expect for air flow on all settings, and I know that the fan speed increases on Max A/C for all fan speed selections Lo - Hi, and ONLY on Max A/C. Speed selections are all accomplished by switching one wire to bypass segments of the series resistor (in series with the armature) much like a rheostat works. It's just in steps instead of a continuous adjustment. On high, all segments except one are bypassed until the selector is turned to Max A/C. Then all segments are bypassed. Thus, when the third speed resistor burns out (most common), the fan won't run unless it's on high. Very common problem on a lot of different makes and models of cars. The segment for Max A/C is used the least frequently, and is always cooled by air flow, so tends not to burn out. Albeit, I have found one case (and repaired it) where that is the segment that failed, and the fan would only run on max speed, Max A/C, i.e. WFO speed.

The Factory issue is 195 degrees F.

Maybe a variance on truck build or destination? I took the OE t-stat out of mine and replaced it. I know for a fact it was original, since I've owned the truck since it had 16 miles on it. Either that, or the OO had a t-stat problem when he drove it off the lot? The t-stat I replaced, was 187 degrees on a 5.0 with M5OD. I'd go look but think I threw the old one away. Is it possible the manuals and autos, or Cali and non-Cali trucks had different t-stats? I just know what was in mine, and what went back in.

 

[NeXtras]

ok guys cut the sh*t, im looking for answers not 5 year olds..

now i can hear all the blend doors etc moving when i move between the settings (Def, Mix, Floor, Off, Vent, A/C, Max A/C)..

now can anyone tell me FOR SURE if the temp control (middle knob) is vaccum or cable.. Why I ask, i was playin around with it and i can only go a little past half when going back to blue (cold).. and i mean half as in right inbetween cold and hot (straight up and down)..

lukkily ill be at ford tomorow working... so i can take a look... but i need some heat considering the highs around here are in the teens

 

[NeXtras]

and BTW, Old Paint.. on MAX AC it SOUNDS to get faster because as Subford said, the Outside air door closes so you will get MORE air coming from the vents... wind (IE outside air) crates resistance..

now STOP your bickering

 

[subford]

The fan moves more air on MAX A/C because you are not taking in outside air.
When the A/C is on normal you are taking in outside air and pressurizing the cab so the fan moves less air. If you roll down the windows the fan would put out the same amount of air on either setting.
Also MAX A/C does max cooling because it does not have to cool the outside air.
Sounds like you need a new manual, look at the below diagrams and you will see what I am saying.

1992 A/C wiring:
http://i54.photobucket.com/albums/g91/subford/AC System/1992A-Cwiring.jpg

1992 Door Positions:
http://i54.photobucket.com/albums/g91/subford/AC System/Hold/ACVacuum3.gif
/

 

[NeXtras]

Wtf!!!! Stopppppp

I Dont Give Two Sh!ts About The Friggin Ac!!! I Have A Heat Issue!!!

IF I WAS ADMIN YOUD BOTH BE ON A LITTLE VACATION! NOW STOPPPPPPPPPPPPPPPPP

Seriously this is the stuff that pushes people AWAY from the site.. god dam...


NOW.. what about that blend door.. vaccum or cable?

 

[subford]

now can anyone tell me FOR SURE if the temp control (middle knob) is vaccum or cable.

It is cable controlled. You should be able to move the temp knob from all the way one way to the other an hear the blend door make a popping sound as they go all the way one way from one position to the other. You do not need the engine running to do this.

Why I ask, i was playin around with it and i can only go a little past half when going back to blue (cold).. and i mean half as in right inbetween cold and hot (straight up and down)..

lukkily ill be at ford tomorow working... so i can take a look... but i need some heat considering the highs around here are in the teens

You have a problem with something in the way of the blend door moving or the cable is dry and hung up. The cable would then need to be freed up or the obstruction removed.

 

[NeXtras]

Now how do i access the blend door?

 

[Mil1ion]

By removing the Heater A/C plenum.

 

[subford]

Now how do i access the blend door?

OK I went and pulled a ducting system and I have it here beside me.
Open the glove box all the way and you should be able to see where the two cables operate the blend door. There is a panel in front of the heater core below the glove box that you can take off. You should be able to see the Blend door then.
If you need photos I can take some photos of the ducting but it is not in the truck so I do not know if they would do you any good or not.

 

[NeXtras]

OK I went and pulled a ducting system and I have it here beside me.
Open the glove box all the way and you should be able to see where the two cables operate the blend door. There is a panel in front of the heater core below the glove box that you can take off. You should be able to see the Blend door then.
If you need photos I can take some photos of the ducting but it is not in the truck so I do not know if they would do you any good or not.

pictures could help... ive had my glove box out before... please and thank you

 

[subford]

pictures could help... ive had my glove box out before... please and thank you

Image 1:

Image 2:

Image 3:

Image 4:

/

 

[Skandocious]

Great post Bill

 

[subford]

Great post Bill

The photos are taken of a 1995 F150 duct but it should be the same from 1992 - 1996.

 

[NeXtras]

agreed skan... very helpful...

so take off the 10mm (looks like that size) bolts there and i can access the blend door?

 

[subford]

agreed skan... very helpful...

so take off the 10mm (looks like that size) bolts there and i can access the blend door?

You would be able to see the henge side of the Blend door and see it move and may be able to reach in and push it all the way to the hot position. At least you could check its operation. The back of the heater core is what you would be looking at with the panel off. With the panel off you can also remove the heater core itself and then you could see the whole blend door. That panel is the heater core access panel.
My yellow handle nut driver fits the bolts and I think it is a 5/16" one size above the 1/4" nut driver.

 

[subford]

The above post should have said "pull it all the way to the hot position" not push.
The photos above all show the blend door in the full cold position and you should be able to reach in with the panel cover off and clear any junk out of it that is in the way of it going to the hot position.