New to the group. If it weren't for the heater problem I probably would never have found this place. Kind of a neat idea exchanging hints among people who have found out the hard way. Kudos to whoever came up with this idea.
To the problem.... I've read through several posts that mention a heater problem ...no hot air, heater core hot, hoses hot ...still no hot air. My problem exactly! Most answers here end with a blend door problem ...start there. My question is : How can it be a blend door problem if the rear heat is not working too? I too have replaced the TStat .... still no hot air. I too have hot hoses ...no hot air. Rear heater is independent of front heater core so blocked core can not be the problem. Neither can the blend door be the problem unless both heaters use the same blend door. ???Which brings up the obvious question ...how ...exactly is the temperature regulated in the rear heater? It has to be some valve or blockage problem .... someboby who has overcome this problem please enlighten us. Other than moving to Miami to overcome the problem ...I'm stumped! Has anyone ever flushed the system and fixed this problem? All the vacuum controls seem to work ...at least to change to a different output they do. I don't have much choice in this, Tiara Motor Coach went out of business taking Mark III with them so parts are going to be a major problem if it's a conversion package problem. HELP! The wife is more frigid than normal.

 

This sounds like you have a strange coincidence. The blend doors get hot, and break... It sound's like a cable or vaccum line is broken.

 

Not a mechanic by any stretch of the imagination but this is what I can not get straight in my mind. If its a vacuum line... okay it controls the blend door...I'll buy that. But what controls the temperature to the rear heater? I don't buy "It's a strange coincidence" Both Blend doors broken.??? Is it possible that there is an actuator within the front heater housing that regulates the amount of heated water that flows to the rear heater? Or is this regulated by the blend door ...the further open the door the cooler the water? Or does a blend door just regulate the amount of air to the front heater core? If this "other" valve is elsewhere on the vehicle...Does anybody have a clue as to where it might be located? I've traced the heater hoses as far as to the rear of the engine and other than a few "Tees" ...no valves or actuators of any knd I can see. Also. is it possible that a freezing rain event has frozen the Blend door all the way open? Thereby allowing too much cold air in. Need a little "Heater" 101 here.

 

Since both heaters are controlled by the same temperature control, it is possible that the cable and/or the vacuum line has broken at the heater control. My first thought was that both blend doors broke at the same time, not likely, or probable, but possible.

 

Thanks for your thoughts. Anything is appreciated. Concede ...Blend doors are a possibility. Control seems more likely.... Need a little "Heater 101 here" ....if you know .... What exactly does the control ...control ...just the blend door? Another possibility is that the replacement TStat is bad ... possible ...as is in my haste it's in upside down ...not likely but possible. I've done dumber things...I guess. Will retrace my tracks. Do so much thank you for responding but if you could give me some guidance on the control removal ... and the heater 101 class I'll be forever indebted.

 

In my 1991 Club Wagon, I get hot air through the rear heater and luke warm air out the front.

 

okay .... it has warmed up enough that the local polar bears have taken off their parkas. thus I can do a little diagnosing of the problem ...hands on. I jury rigged a bypasss of the heat control "switch" .... I have heat to the rear heater and luke warm to the front .... assuming diagnosis of bad control is correct. Anyone have a clue how to remove the panel covering the dash? Are there clips behind it or does the front control on the radio have to be removed to expose some screws? Or do you have to completely remove the radio to get at whatever mechanism secures the switch? This is a 1997 E 150 5.4

 

i also have a '97 e150 with 5.4. you can remove the radio in about 10 seconds. there are 4 holes in the corners of the faceplate. you push a straight probe into them & it releases a catch. i bought a tool from pep boys - it's nothing more than 2 u-shaped wires. you push one in the left side holes, one in the right side holes, push, then pull to the outside, & the radio pops right out. my van's parked too far away right now to check, but i believe the heater controls come out the same way.

 

Well ...that didn't work .... seems the last shade tree mechanic bent the clips on the radio out too far with his make shift tool so it ended up the panel came loose while trying to remove the radio. This is exactly why I'm not an airline pilot! It has turned out okay though ....after removing the cowling, the center console, both dash panels, the radio, the entire heater/AC control panel and disassembled the heater/ac control panel ...I have the part in my hand.... piece of cake! I am having my doubts though ... as it turns out the heater control is electric (similar to a comutator) and not a vacuum control as I suspected. Hmmm ...the bypass I did involved the selector switch for ac/vent /defrost unbeknownst to me. Guess I'll replace it too. And this folks is why I'm not a rocket scientist! Duh

 

Well ...it was the blend door! Don't ask me how it affects the rear heater but it somehow does. Maybe the heaters are hooked up in series so with the front blend door broken it cools off the water in the front core so that by the time the water gets to the rear core the water has cooled sufficiently to cause it to seem as if there is no heat. Thanks pfogle you diagnosed it correctly.

 

I have 1991 Econoline 150 . The issue I am having is that the elderly gentleman that I bought it from was told not to turn on the rear heater/ac unit and once he did it started causing issues with the front unit. The only way I can get the blower to engage is to move the air vent controls around until it turns on but it's always on the vent setting once it's running then I can change it from low to high with no problem. If I try to place it on the AC/Heater settings it does not work at all. I have not turned on the rear unit bc I was told the blower was seized up and will cause an issue. Can someone please give me some ideas on what , where and how to trouble shoot. This is my first time having to fix an issue like this . Thank you