HVAC question

[vwhugger]

OK, in the huntin' shack, which is a mobile home, the furnace has been acting up this year. It's a 1966 and the furnace is an Intertherm(LP).

For starters, why are there two(2), what appears to be, thermocouples?

I can see the one by the pilot but can't tell where the other one goes unless I remove the whole burner assy. But it's near the other one.

I can light the pilot and it remains lit and the main burner will light also and everything seems to work normal and it will reach the thermostat setting and then it'll shut off. On the next cycle, the main burner may or may not reignite. Sometimes it works normal but sometimes there's a small explosion which blows the pilot out. It's a little unnerving so I quit using it.

A new furnace is in store for next year but if it's something simple I may fix this one.

Anyone got a little direction here?

 

[SDWhirlwind]

Re: HVAC question

The old Intertherm furnaces used a 2 stage gas valve. First stage came on when thermostat called for heat, a few seconds after burner lite the 2nd stage would open up to full burn. Probably a 100k BTU so first stage would be 30k or so and then rated capacity with 2nd stage as it increased pressure. The piece that sticks out at the back of the gas valve is what performs this function. No fix except a new valve!

The 2nd 'thermocouple' you see is only a vent tube. Vents LP from diaphram of gas valve as they operate on and off. Used on alot of the old chit! Should be a flame there at least part of the time but not full time.

That era of Intertherms were popular in trailers. Were inefficient and a pain in the ass. Especially to get it lite at times when there was a strong wind, had to climb a roof more than once and cover chimney until it was lite. Lost hair and whiskers more than once liteing those folkers.

Doubt you can find many of the parts for them anymore and replacement is the only good fix for the bastards. Cracked combustion chambers was also very common after 15-20yrs.

 

[DoubleBarrel]

Re: HVAC question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SDWhirlwind</div><div class="ubbcode-body">The old Intertherm furnaces used a 2 stage gas valve. First stage came on when thermostat called for heat, a few seconds after burner lite the 2nd stage would open up to full burn. Probably a 100k BTU so first stage would be 30k or so and then rated capacity with 2nd stage as it increased pressure. The piece that sticks out at the back of the gas valve is what performs this function. No fix except a new valve!

The 2nd 'thermocouple' you see is only a vent tube. Vents LP from diaphram of gas valve as they operate on and off. Used on alot of the old chit! Should be a flame there at least part of the time but not full time.

That era of Intertherms were popular in trailers. Were inefficient and a pain in the ass. Especially to get it lite at times when there was a strong wind, had to climb a roof more than once and cover chimney until it was lite. Lost hair and whiskers more than once liteing those folkers.

Doubt you can find many of the parts for them anymore and replacement is the only good fix for the bastards. <span style="font-weight: bold">Cracked combustion chambers was also very common after 15-20yrs.</span> </div></div>
read this as a "possible" carbon monoxide hazard. might want to get a co detector just for safety. my .02

 

[vwhugger]

Re: HVAC question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DoubleBarrel</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SDWhirlwind</div><div class="ubbcode-body"> <span style="font-weight: bold">Cracked combustion chambers was also very common after 15-20yrs.</span> </div></div>
read this as a "possible" carbon monoxide hazard. might want to get a co detector just for safety. my .02 </div></div>
Thanks for the concern but I'm quite cautious with stuff like this. Maybe near the point of paranoia.

I have numerous smoke detectors, co detectors and explosive gas detectors around the place. And I never use the furnace overnight when I'm sleeping. I use electric in that instance.

 

[vwhugger]

Re: HVAC question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SDWhirlwind</div><div class="ubbcode-body">The old Intertherm furnaces used a 2 stage gas valve. First stage came on when thermostat called for heat, a few seconds after burner lite the 2nd stage would open up to full burn. Probably a 100k BTU so first stage would be 30k or so and then rated capacity with 2nd stage as it increased pressure. The piece that sticks out at the back of the gas valve is what performs this function. No fix except a new valve!

The 2nd 'thermocouple' you see is only a vent tube. Vents LP from diaphram of gas valve as they operate on and off. Used on alot of the old chit! Should be a flame there at least part of the time but not full time.

That era of Intertherms were popular in trailers. Were inefficient and a pain in the ass. Especially to get it lite at times when there was a strong wind, had to climb a roof more than once and cover chimney until it was lite. Lost hair and whiskers more than once liteing those folkers.

Doubt you can find many of the parts for them anymore and replacement is the only good fix for the bastards. Cracked combustion chambers was also very common after 15-20yrs. </div></div>

OK thanks Dennis.

I think I'll disect the gas valve to see how it works. What about the possibility of putting a newer valve on it without that vent line? Lot's of them on eBay. I'll probably just turn this into an learning experience and replace it (furnace) next year though. I have electric and wood also so I can get along without it.

One more question, does the combustion air come down from the roof jack? From what little info I could find, I got the impression that it serves a twofold purpose. I was thinking maybe a critter has a nest in the air intake portion causing combustion problems. Maybe when the main burner ignites, the whole system gets O2 starved and everything goes out.

Just a thought.

One more thing, I'm pretty sure the combustion chamber is ok. There's never been any indication of a problem.

 

[SDWhirlwind]

Re: HVAC question

The vent hole is only proprietary(think that is what I want to say) to that brand/year/design of gas valve. If a gas valve doesn't have one it is because design eliminates it, not a requirement unless it is actually tapped for such. However you MUST use a 2 stage gas valve and perferably for insurance purposes the brand/type the furnace was designed for. Some insurance companies can/will refuse coverage if this is not done. Probably moreso now but I have been out of the business for 10yrs so guessing it is worse now. A single stage gas valve will cause 'hard' starts and can occassionally or repeatedly blow out the pilot if they open @ full throttle! DO NOT buy a used one off Ebay as there is no way to verify history or operation issues. If you can find a new one that would be best but then again with manufacture date/shelf life issues even then an insurance company could make this an issue in event of fire, a death etc.

Second, yes the roof jack/chimney is designed to bring in fresh air/combustion air on the outside, flue gas on the inside. This design also helps to keep chimney pipe warm so it will draft better. ALL mobile home/trailer house furnaces and water heaters are different than other residential heating systems. They are all 'sealed' combustion, not completely air tight but pretty close. Furnaces usually bring in combustion air via chimney and water heaters either same or from underneath home.

These Intertherm furnaces had a built in duct from the chimney pipe to the bottom of furnace. A hole about 1" or a bit more was located at the bottom I think towards the back but different designs/years/sizes may vary. This hole brought the air into the combustion chamber. It was easy during the summer for mice to haul shit into this small passage way and block the combustion air or reduce it. This would cause suffocation of flame etc. Furnace might have to actually be removed to clean this out easily. Only seen it happen a couple of times.

As for combustion chamber you can check it easily because of the access door being as big as it is. Use a mirror and a flash light and you should be able to see entire surface area and determine if there are any cracks. Also removing the fan assembly makes it real easy to check top.

Just be carefull with how you repair, modify, repair these or any other LP items, especially older units as liability issues with 'do it yourself' repairs can get real sticky if something goes south.

HTH

 

[vwhugger]

Re: HVAC question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SDWhirlwind</div><div class="ubbcode-body">The vent hole is only proprietary(think that is what I want to say) to that brand/year/design of gas valve. If a gas valve doesn't have one it is because design eliminates it, not a requirement unless it is actually tapped for such. However you MUST use a 2 stage gas valve and perferably for insurance purposes the brand/type the furnace was designed for. Some insurance companies can/will refuse coverage if this is not done. Probably moreso now but I have been out of the business for 10yrs so guessing it is worse now. A single stage gas valve will cause 'hard' starts and can occassionally or repeatedly blow out the pilot if they open @ full throttle! DO NOT buy a used one off Ebay as there is no way to verify history or operation issues. If you can find a new one that would be best but then again with manufacture date/shelf life issues even then an insurance company could make this an issue in event of fire, a death etc.

Second, yes the roof jack/chimney is designed to bring in fresh air/combustion air on the outside, flue gas on the inside. This design also helps to keep chimney pipe warm so it will draft better. ALL mobile home/trailer house furnaces and water heaters are different than other residential heating systems. They are all 'sealed' combustion, not completely air tight but pretty close. Furnaces usually bring in combustion air via chimney and water heaters either same or from underneath home.

These Intertherm furnaces had a built in duct from the chimney pipe to the bottom of furnace. A hole about 1" or a bit more was located at the bottom I think towards the back but different designs/years/sizes may vary. This hole brought the air into the combustion chamber. It was easy during the summer for mice to haul shit into this small passage way and block the combustion air or reduce it. This would cause suffocation of flame etc. Furnace might have to actually be removed to clean this out easily. Only seen it happen a couple of times.

As for combustion chamber you can check it easily because of the access door being as big as it is. Use a mirror and a flash light and you should be able to see entire surface area and determine if there are any cracks. Also removing the fan assembly makes it real easy to check top.

Just be carefull with how you repair, modify, repair these or any other LP items, especially older units as liability issues with 'do it yourself' repairs can get real sticky if something goes south.

HTH </div></div>

Great info, thanks a lot.

My wood burner also uses outside air for combustion for mobile home use. I had to buy an extra little kit for it that goes thru the wall.

Thanks again, J. I'll let you know if I come up with anything.