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Discussion Starter #1
I have an issue that I'm trying to get dialed in. I recently had some work done to my 2005 6.0, I upgraded my turbo and had an egr delete done on it. This was done in the summer so the issue I have hasn't come up until now. I drove my truck the other day when it was close to zero outside and I had no heat, I drove about 15 miles and stopped at a store after the initial trip I went a few more miles down the road and the heat was working. Then after driving again I had no heat. For some reason the heat seems to come and go whenever I cycle the ignition, I know all about the light switch problem on the climate control panel, it's happened to me several times during my ownership, this heat thing is new to me and I haven't seen anyone else post about it....help!
 

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Check your coolant level. When they are low the heat can be spotty or outright not work because its high in the system.
 

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Discussion Starter #3
Thanks, that was the first thing I checked, it is at the full level in the degas tank, however I'm wondering if there's an air bubble in the system!
 

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That's possible, but the system will burp/self bleed typically. So unless you just added a bunch of coolant I wouldn't think that's your issue. Typically the system will purge the air after one or two good drives.

Check your heater control valve for operation. Its on top of the engine on the RH side back by the firewall. It was a gray vacuum hose going to it. You could pull and plug the hose and pull vacuum on the valve with a vacuum pump and see if you have heat. If you get heat the valve is good, if not the valve is bad and you've found your problem. If the valve is good and you get heat it means there's an issue somewhere else in the system because it would indicate it is not directing vacuum to the control valve when the heat is on like it should.
 

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Discussion Starter #5
Thanks for the help so far! The temp was in the upper 30's today so I thought I'd do some investigating, the heat barely trickles out when I have my setting on 90. Not the air, the blower is working fine, I was also told to manually move the heater control by hand and tie it in place, still no real heat. I've been told to check my potentiometer whatever the heck that is, I've been told that my truck may or may not have one.....does anyone know?
 

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A potentiometer is an analog device that increases or decreases something (current, resistance, etc.) as you turn a dial. I can't say if your truck has one or not; I have the non electronic temp controls in mine so no point of reference.
 

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TKO, even with the manual controls, the air direction dial is VAC and the fan speed is a switch but I believe the temperature control rotary dial is a pot.

Here's the backside of the manual controls.



Here's some general info on checking Ford's controls, I haven't investigated to confirm this is exactly what is in the manual control dash of our generation of truck:

http://www.factoryairtemp.com/Upload/Factory Air/documents/Tech Tips/FA4S 356 FORD'S BLEND DOOR ACTUATOR.PDF

Regarding the climate control, I don't know anything about it so I don't know if it has a pot to check or not. My guess would be no, that it's all solid sate run off a board, but again, I don't know.

Also, a pot issue generally results in too cold or too hot, just not changing enough or at all. Not varying random temps.
 

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Discussion Starter #8 (Edited)
Thanks guys, it's looking like mine is the heater control valve, I have one on order so I'll know in a few days! My truck has the electronic control so I guess I don't have a potentiometer in mine.
 

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That would make sense Phil. Old systems used cables for temperature control so you could adjust the degree to which the temperature door was open, thereby controlling the mix of cold and hot air. . If there's no cable I'd have to agree that it must be done with a pot, because I know of no easy way to use just some vacuum. The doors controlled by vacuum are either open or closed. Honestly, I've never had a climate control issue on the heating side in anything built after about 1990. AC systems sure, but the heat always seems to work so long as the core is good.
 

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That's possible, but the system will burp/self bleed typically. So unless you just added a bunch of coolant I wouldn't think that's your issue. Typically the system will purge the air after one or two good drives.

Check your heater control valve for operation. Its on top of the engine on the RH side back by the firewall. It was a gray vacuum hose going to it. You could pull and plug the hose and pull vacuum on the valve with a vacuum pump and see if you have heat. If you get heat the valve is good, if not the valve is bad and you've found your problem. If the valve is good and you get heat it means there's an issue somewhere else in the system because it would indicate it is not directing vacuum to the control valve when the heat is on like it should.
I was thinking this was a valve to merely shut off coolant flow to the heater core when the A/C was on Max?
 

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It shuts off flow to the heater core whenever the heat or defrost is not selected on the function dial.
 

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Discussion Starter #12
So another question here....can I bypass the heater control valve until my valve comes in? I ordered one online and it wont be here now until around the first week of Feb.
 

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Take it out an put in a straight piece of tubing, but it will be on max all the time. The best solution would be to put in a manual ball valve and that will give you some degree of control, even though you have to stop and raise the hood to control it. Don't forget to plug the vacuum hose.
 

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If it is the heater control valve I have always had some heat felt on the hose up to the valve. It is conceivable that the lever to vac diaphragm and the shaft are no longer locked together for some reason and the heater control valve cycling leaves it off at times and works as it should others.

The valve is normal open, vacuum to close. When I have checked the valve is only supplied vacuum on ATC systems when the a/c is on and temp diff cab to set temp is a big delta. when the temp in cab gets to set and ambient is not over something about 100F then it shouts off the vacuum and allows coolant to flow into core in case it needs to moderate vent discharge temp by mixing some warm air with cold.
Does it do the same thing if you adjust the set temp to the highest number? If cabin temp sensor is reporting the wrong temp (bad sensor) then setting to highest number is an override and you will get heat anyway if it is that problem.
 

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Discussion Starter #15
**Update on heat**

I changed out the heater control valve and still no heat to speak of, even if I have my heater control on 90 it barely warms up. I'm at a loss as to what I should look at next! If anyone has any ideas please let me know....my wife is looking at this as an excuse to sell my truck and go back to a gas rig. This is the first real hiccup that this truck has given me so I don't want to get rid of it.
 

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Have you checked to see if the heater core is plugged?
 

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Discussion Starter #18
No that was my next guess, Both hoses feel the same temp wise but it my not be getting through to the core. I have no idea what could cause a blockage though!
 

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The junk usually floating around a 6.0 cooling system. Even if you've flushed the system the heater core can still be contaminated because unless you go through the backflushing procedure it only gets flushed so well (assuming the heat was on when you did the flush, which I'll admit I've forgotten more than once).
 

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The good news is should you have to replace it, they aren't stupid expensive (Just over 100 for OEM if I recall) and it's not that hard to do other than I imagine unlocking the 2 coolant lines at the firewall might be a challenge with the engine in the way. I changed mine while the engine was out just because of the miles on it and the fact that the connections were easy to get at with the engine gone. Regarding pulling the core on the inside...not bad at all.
 
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