Ok, just started to bench test my gas heater I bought a month or so ago Friday night. We got it to start and heat well. Everything seems to work great except one thing.
The heater is the late model BN4 that came out a '76 bus just like mine. The problem is that once the heated air reaches a given temp the temp regulating switch that is mounted on the ducting cuts the whole thing off. It sits for about 2-3 mins and then fires back up automatically.
The temp switch from my understanding should only cut off the fuel pump when the temp reaches a give temp. Not the fan too. I understand that the fan should continue to blow air across the heat exchanger and into the vehicle until the warm air falls below the specified temp and then the fuel pump kicks back in to heat the air once more and so on and so on... But my just shuts off completely.
Has anyone had this problem or know how to fix it. I posted the question on the type2.com list but nobody seemed to know, or maybe just didn't have time to respond. Anyway I want to get the heater installed before my engine gets here (about 1-1 1/2 weeks) to make it easier. Any input would be appreciated.
You will probably find that the in duct thermostat...that two pronged strange looking thingy...is not the culprit. The problem is most likely the high temp cut-off switch that is mounted in the rubber plug in the top of the flame chamber. It is a round bi-metallic diaphram. If it has any dents in it...it will be inaccurate. If the crimped wire assemblies are bent...it may be innaccurate. If the airflow through the unit is impeded...it may be cutting off too soon. This is an emergency switch...so it cuts off everything. You might also check the main thermoccouple...that rod device sticking into the chamber. It should have a resistance value. For the most part...it sounds like the high limit switch described earlier. Also ifyou are running too much fuel through the unit....check your volume adjustment on the pump... it could also overheat. ray
Hey Ray I will see what else I can find out about that other stuff that you metioned. Something I forgot to say in my previous post was that after it kept cutting off like that I decided maybe I had my wires switched that hook to the temp regulating switch so I switched them. Don't know what exactly it did but it allowed the heater to run practically as much as I wanted. Nothing cut out. The air got really warm and seemed everything worked great. Not sure why switching the wires on the temp reg switch did this, but it did. Of course I would never run it in the bus like this. I want all safety equip to be functioning properly, but thought I would throw that in too.
Well...that could be it...by the way..which part are you calling the temperature regulating switch? The thermostat in the ductwork or the unit with the long probe and the four wires? Ray
The temp regulator switch I am referring to is the one in the ducting that the bowden cable attaches to. It is supposed to control air temperature. The other one should be the flame detector switch that has the quartz probe to make sure the fuel/air mixture is igniting and if not after apprx 2-3 mins it will shut the heater off and then the safety switch has to be flipped. Do you know of any wiring diagrams for the late model BN4 fuel metering style heaters. Someone has cut and reconnected the wires that come from the duct temp switch and I just want to make sure they are connected in the correct places. And everything else of course. Do you think that a bad relay would allow the heater to run and heat just fine but cause the fan not to blow when the temp reg switch does its job on cutting the fuel pump. Bad relay cause the fan not to blow also instead of just the fuel pump? I really want to get this thing working properly so I can get it installed. My engine will be hear about this time next week ready to be put in! I'm excited!
Steve,
Thanks for the offer, but with all the money I have spent in the last month with the engine rebuild and everything else I'm about tapped out. I wouldn't mind having another heater around, but just don't have the cash right now.
Aha!...The temperature regulation cable your are speaking of is the culprit. By the way is this the heater with the green knob on the dash...turn it clockwise ...has a timer? If you are using the main lever to regulate heat....the one on the floor (411/412) or the dash (bus) that has a brown..or brown and white wire...that cuts it off. That brown wire is the main ground for the power relay. It is designed to cut off the power if the body vents are not all the way open...because that creates an obstruction...that curtails airflow and causes the high limit switch to kick off too early. The heater temp on the late model bus units is set by the green knob on the dash. DO NOT wire around that failsafe...or you will burn things up. The bowden cable itself should not be connected to anything electronic. The in duct two wire thermostat acts in concert with the green knob on the dash. You set the knob a certain amount of turn...and the heater runs until the corresponding temperature is reached in the duct...then the heater cuts off...and refires when it has cooled down below the set temperature. If you need more heat..turn the dash knob up higher. At highway speeds...full turn on the knob...should run nearly continuously. One of the problems that can happen...is when the duct thermostat is placed too close to the heater unit...in a non stock location. Then it cuts off too quick for you to feel good heat without turning the green knob up too high. The main heater cable lever...that moves the air box levers in the back should always be at full open while running the heater..or it will have temperature problems because the airflow over the thermostat is too restricted (backed-up). Also..be sure the auxiliary fan in the back that usually hangs in the center of the bay...and connects to the draft pipes of the heater boxes is running and has no kinked hoses or ripped hoses....and be sure its running in the right direction.... this is very common...make sure yellow goes to yellow and brown goes to brown...or you will have the same problems you are having.Ray
Hey Ray,
I am sorry if I didn't say this earlier, but as of right now my heater isn't actually in the bus. I have just been bench testing it and maybe the way I have hooked it to the battery is causing the problem. I am kind of a rookie at the gas heater scene. It has two wires, red, gray, that I hook via some alligator clips to the +, and then the main ground that I hooked to the - of the battery. This lets the heater kick on and run great until the air gets to a given temp where it then shuts completely down, I don't think the fan should cut off, but just the fuel pump. Maybe its the way I have it wired. I need to get my hands on one of the stock type timer switches to install this bad boy properly. Do you have one you want to get rid of or know anybody that does? My heater doesn't use any of the heater ducts on the bus, but just the main on that goes thru the firewall and then under the back seat. I don't have much need to have the stock fan cause I won't be using my heat exchangers when I get the engine back in. I got some 411 tubes that have been stripped down and a S&S header. But back to the heater... Maybe my wiring to the battery is the prob? Think the way I have it hooked up might be wrong?
Bob,
I had checked with heaterman for a bracket to mount my heater cause I didn't have one and he quoted me $45.00. I sent him an email saying I was interested and asking him about another part and he never got back with me. Also the next day after sending heaterman an email about the bracket Ken Madson at the bus co emails me and asks if I still need a bracket. I say yes. Bracket is on its way for 10 bucks. Quite a bit cheaper and he is very responsive. Easy guy to deal with. ([email protected]) I am also having him send me a relay just to try. For 10 bucks too. If its not the relay at least I have an extra just in case down the road something happens.
I think this problem is getting a little more complicated than it really is. Basic bottom line is that the temp reg switch located in the duct that is connected to the bowden cable is working, but for some reason the fan is shutting down along with the fuel pump, instead of just the fuel pump. If I "hot wire" that switch then heater runs no prob and just keeps getting hotter and hotter. So of course I shut it down. Something is causing the fan to cut off when only the fuel pump is supposed to. Also this heater is in no way associated with the stock heating ducts/fan or anything. It has its own duct and own fan. The blower fan in the engine bay that is on the bus stock plays no role in the operation of this heater.
Thanks for everyone's input.
Let me know if you come up with anything. And when I find the prob I'll post it here so if anyone else has the prob it might help out.
Thats a little more explanatory. You really need to have the full harness hooked up with all relays...and the timer switch. The auxiliary fan is a must....the crank fan even without heater boxes is not enough flow through at idle to keep the high limit switch from overheating. The heater appears deceptively simple...but I challange you to trace the overheat switch path down....its actually more complex than it looks within the quadruple relay you have in the system. The symptom you are speaking of is due to overheating. There is a high limit switch in a rubber plug in the top of the heater body. Its a little disc looking thing with two wires. It can shut the unit down dead. If you dod not have enough airflow...it will happen. Yes...you can swap power leads around to get it to stay on. I have been this route before....20 years ago. It burned the heater pipes off my 411 before I could rip enough wires out of the relay to shut it down. I would bench test for component testing...but I would for sure also put the whole harness and all components on line to be sure everything is wired up correctly. While you have the fuel pump out...it would be good to do the volume test on it to make sure it is not running too hot or too cold. When the unit shuts off...do you have to punch the reset switch on the black relay? And do you have the two in line fuses that goe back by the relays installed yet? One of those..the 25 amp one...is supposed to go to the olive green double wire that feeds from the high limit/overheat switch. Ray
Heater Problem solved. I had called a guy by the name of Robert Keezer that Ken Madson @ thebusco.com put me onto. Robert called me Sunday night and after spending a while on the phone with him and us walking thru the wiring and all to make sure it was all correct we found it was. Then from there with two heads working we found out that the flame detector switch wasn't pulling its weight. It was out of adjustment. It wasn't switching power off from the glow plug and then to the normal operating position. So with a slight adjustment it is working great. Thanks to all who gave me input on this. And thanks especially to Robert for spending the time over the phone to help me out. If anyone needs help with gas heaters he does this as a side/hobby thing and seems to know his stuff pretty well. He email is [email protected]. Really nice guy and super easy to deal with. I would recommend him to anyone!
