99 F350 No heat

[AlanB]

Drove the one ton in too work today and had no heat.

Temperature gauge came up fine, and I am assuming that the engine is producing heat. (it would be hard for it not too)

In the past couple times I have used it (I am an occasional driver of this vehicle) I have had to cycle the heat knob from hot to cold to hot to get the heat to "start", but it has always then worked.

I am guessing, and I have the manual so I will go read as well, that the heat system is Vacuume controlled on this thing, and as I have problems with the vacuume engagement on my 4wd on this truck I am suspecting that they are interrelated problems.

Anyone have experience or suggestions of problem areas to check first?

 

[luscsmith]

first thing is to make sure the coolant level is correct.

 

[AlanB]

first thing is to make sure the coolant level is correct.

Yes, my coolant level is correct, verified each fill up.

I believe this to be a "controls" problem, not a "heat" problem per se.

 

[GBeck]

I have a 97 150 that had a recall for this issue...not sure what the part was could be the same thing

 

[Eagleview]

Is it a Diesel with a vacuum pump or is it gas with a mainifold fitted hose ? Can you hear any vacuum leaks under the dash ? It could be a perished/disconnected vacuum hose , a leakin "O" ring on the control lever , or a cracked resevoir . If it is a Diesel the vanes in the vacuum pump could be crook .

 

[Highbeam]

I'll assume it is a diesel. I have a 2000 model F350 with diesel and the HVAC is controlled by vacuum. The auto locking front hubs are also controlled by vacuum and are known to be crappy. The hubs are engaged with a short 6 second burst of vacuum and then the valve shuts off. If the hubs are leaky then your HVAC will go to defrost until the vacuum pump (electric, on the inside of the pside fenderwell) makes enough vacuum to suck it back to the original setting. I don't believe that the heat setting moves when vacuum goes away. Just the direction of the heated air.

The heater cores always have hot water, no valve. So to verify that the heater core is getting hot simply feel both heater hoses for temp. If they are both hot then you know that it is a control issue.

 

[AlanB]

It is a diesel. It does have the vacuum pump thing on the right firewall, it does appear to be sucking, and switching off appropriately. I am pulling about 16" of mercury which seems a bit low, but I am guessing it would be close. It does microswitch off the pump when connected.

My heater hose's (whatever) are getting hot, and I was guessing there was no turn off's, just redirects of airflow.

I pulled the knob off the face, and the stem is turning and free, so from the front it appears to be working.

So where I am at now, is best guess, it is under the dash somewhere in either the vents, or the control.

Through the graciousness of this board the master book is on it's way.

I figure the next step is too pull the dash and poke and peer a bit.

Just for grins and in sympathy I think my 98 Chevy Z71 decided to puke a heater core yesterday, ain't it great

Thanks guys.

 

[J_J]

It is a diesel. It does have the vacuum pump thing on the right firewall, it does appear to be sucking, and switching off appropriately. I am pulling about 16" of mercury which seems a bit low, but I am guessing it would be close. It does microswitch off the pump when connected.

My heater hose's (whatever) are getting hot, and I was guessing there was no turn off's, just redirects of airflow.

I pulled the knob off the face, and the stem is turning and free, so from the front it appears to be working.

So where I am at now, is best guess, it is under the dash somewhere in either the vents, or the control.

Through the graciousness of this board the master book is on it's way.

I figure the next step is too pull the dash and poke and peer a bit.

Just for grins and in sympathy I think my 98 Chevy Z71 decided to puke a heater core yesterday, ain't it great

Thanks guys.

If I remember right, I believe that the heater line has a vacuum switch in-line. This valve is what keeps the hot water from flowing through the radiator.
Check to see if it is working by applying a vacuum from a good source, or get one of those brake bleeder vacuum pumps, and pump some vacuum to see if the switching valve is operating normally. Check and see if the line behind the valve is hot, then take off the inside cover and see if the radiator is hot . For instant use, you could cut that valve out of the system and splice the hoses together. That valve is there to keep heat out of the A/C part of the system for summertime use. Just plug up the vacuum line and fix or replace the valve later.

Also check out that vacuum reservoir.

 

[Eagleview]

It is a diesel. It does have the vacuum pump thing on the right firewall, it does appear to be sucking, and switching off appropriately. I am pulling about 16" of mercury which seems a bit low, but I am guessing it would be close. It does microswitch off the pump when connected.

My heater hose's (whatever) are getting hot, and I was guessing there was no turn off's, just redirects of airflow.

I pulled the knob off the face, and the stem is turning and free, so from the front it appears to be working.

So where I am at now, is best guess, it is under the dash somewhere in either the vents, or the control.

Through the graciousness of this board the master book is on it's way.

I figure the next step is too pull the dash and poke and peer a bit.

Just for grins and in sympathy I think my 98 Chevy Z71 decided to puke a heater core yesterday, ain't it great

Thanks guys.

If both of your hoses are hot it means the hot water is circulating which in theory should warm the cab . The problem would be the "BlenDor" which is a vacuum actuated or HIVAC electric actuated flap/door that mixes cold air and hot to give a set warm temp . Sometimes these doors jam , strip the drive spline that goes into the actuator motor and sometimes the HIVAC/vacuum device seizes or loses power which stops the door opening , preventing air from travelling through the heater core and exiting the vents . You may be able to see the HIVAC/vacuum unit on the side of the heater box (usually a gray flat device or possibly a diaphram pot) . By removing the mounting screws it is possible to turn the "Blendor" shaft to check if air can be made to come out the vents .

 

[Eagleview]

This is a picture of the Air Blender door shaft "BlenDor" in a Ford Falcon car , it is out of my CD workshop manual . It would be simillar to yours , if this is your problem it may help . The white shaft is what the doors are attached too . The motor is splined to the shaft , this is what usually gives trouble .