mobilehomerepair.com

I had trouble getting to any archives and hope I searched far enough in past posts. If I missed one please redirect me, I don't want to repost an issue that has been solved - thanks

I have a Coleman 7700A-856 gas furnace in my 77 Shulte mobile home. I've been here 3 years and every winter the pilot blows out about 3 or 4 times and then works fine the rest of the winter. This year, it works fine when I'm in the house and moving around, but if I leave or go to bed for the evening, I wake up to a 40° house or come home to one.
I change the filters regularly, but I've never opened up all the panels and cleaned the whole thing out. my house is very dusty, could this be as simple as a thorough cleaning? The blades on the squirrel cage blower are pretty dirty.

Decided to replace thermocouple since i was disassembling this beast anyway. When I removed sight glass mounting ring to access the thermocouple, I found a bunch of what I call Rusty furnace dust. I vacuumed out the burner box and see no apparent holes or cracks. I am currently looking at how to remove the blower assy. the control box and switches are mounted on the front of the blower, it may have to be removed to facilitate blower removal.

Slid Blower assy. out of holders and found fins in squirrel cage 99% clogged with very fine dust. I think I should have cleaned this thing out when I first moved in, yuk! Used brush and shop vac to remove dust. No holes or damage to heat exchanger, very good news.

Opened cover exposing the A-coil, just what I was afraid of, really fine dust clogging the fins. I used a brush and the shop vac and got what I could. I brushed and vacuumed everywhere and really cleaned it up a lot. The cover to the A-coil is a little southern engineered, so after reattaching it the way it was originally, i used good metal repair tape and sealed it all up.

I fired up the pilot and called for heat, yee haaa... works great. It had cooled off enough while I had it dis assembled, it took about 1/2 hr to warm the house back up to 68°. When it got to temp, it shut down, I peeked, the pilot is still lit, I'm waiting to see if it will call for heat again and really fire up. It's almost 60° outside today, so I may have to wait till the sun goes down.

Now that I'm familiar with it, I'll probably order some cleaner for the A-coil from these guys and service it again in the spring.

Hi,

Maybe this will help :

http://www.mobilehomerepair.com/hvac/articleshvac.html


You can click Search in upper tool bar underneath HOME and type in related words.


If it can happen, I've most likely covered it a time or four, LOL.



Holler if you need anything.


Thanks,
Robert

Thanks for the reply Robert,
After the great cleaning i gave the whole unit yesterday, I thought my problem was solved. When it finally called for heat, all went well through the night until about 3:00 AM this morning, it felt a little chilly so I got up to check it out and the burner lit as I was walking up to it and then the blower came on, I was so happy it made it a whole night without relighting. it went through it's heat cycle and then went off.

Only 15 minutes later, it did it's usual spin up to get ready to fire up, then nothing, pilot light out again. What is making the pilot go out?

The only symptom I can tell you is, when I try and relight the pilot, it's awfully breezy in there, and my matches keep blowing out before I get it lit. Could my roof cap be damaged?

Hi,

That's a good possibility.Shouldn't be any breeze.


Make sure roofjack extends above roof peak and weather car/crown are on tight and all is straight with no damge inside or out.


Thermocouple, gas valve, gas pressure and downdraft are only possibilities.


When you installed the digital t-stat, what didn't work or was not right ?


Thanks,
Robert

The roof jack and cap are in great shape and in good position. This may be a stupid question - there is a guard by the pilot light, I may have (pretty sure) bent that out of the way when I changed the thermocouple the first time. What is the proper position for this guard in relation to the pilot and the thermocouple? Is it a wind block?

Part II -The thermostat I bought was a ac/heat digital unit. It appeared i was going to not use the AC half of the thermostat because of my furnaces on board fan and heat/cool controls. Since it was kind of an expensive unit, I opted to look for a heat only digital. Not finding one readily, I swiped the one out of my camper, and it works so well, I just left it alone. I'm selling the camper and will need to re investigate getting a digital unit for the house, any suggestions? Do you sell a heat only unit that is compatible with my furnace?

Hi,

You can use what you had in most cases. You wire the two wires to RH and W.


Set t-stat switches to Heat and Auto ALWAYS in both seasons.


Set furnace switches to Auto always and then heat/cool depending on season.


Set temp lever where you want it to stay.


Furnace and a/c will cycle as supposed to. Instead of switching from heat to cool and vice versa at t-stat, you do it at furnace.



Honeywell and White Rodgers, preferrably from an hvac supply is best.



Thanks,
Robert

Thanks for the info on thermostats. My furnace stayed lit all night last night and into today, then about 6:30 this evening and ever since, pilot light gets blown out after it warms up the house once.

When I cleaned out the fins in the main blower motor, I held it in place with one arm, and rested it on the ledge on front of furnace. This way I didn't have to disconnect all the wires to the motor. The bad part is, I couldn't get to the booster blower and clean it.

Is there a sail switch on the booster motor?
Does anyone have an exploded view of my furnace?
Is there a sail switch of some sort on this furnace?

I'm also going to locate a post on how to trouble shoot the gas valve. I saw it here somewhere the other day.

Hi,

Call Mark toll free after 9 AM CST Monday to purchase a wiring and parts diagram.


Booster Motor has a centifugal switch inside and it cannot be bought seperate from motor.

Booster motor is easily accessible, remove screws around wheel housing, disconnect wires and voila.


Gas valve testing needs input gas pressure check, 24vac at gas valve entire cycle, manifold gas pressure check.


Thanks,
Robert

EDIT - Thanks Robert, You're the greatest. After today, if I don't get it going, I'll call a professional. There is still a definite breeze inside my burner box, but i can't find the hole anywhere.

I Had one more observation - After lighting the pilot and screwing the sight glass back on, i bump the thermostat up to call for heat. looking back into the sight glass, i see all the flame hitting the deflector but it seemed like the pilot light was lighting and going out, lighting and going out. If it is out when the gas valve shuts off, no heat next time.

Is this the sign of a dirty pilot or a gas valve going bad?



Again, Let me say thanks for all your help and timely answers. The internet and people like you, helping others out is what it's all about!!

Hi,

Thanks for the kind words and you're very welcome, happy to help.

Aside from downdraft through roofjack blowing pilot out, here are other possibilities:

Damaged or dirty/clogged pilot burner

Damaged, dirty or clogged pilot tube

Bad thermocouple

Bad gas valve

Hole in heat exchanger



Thanks,
Robert

Solved -
I called an HVAC guy out and after inspecting my furnace he won't even relight it.

He used a mirror and looked behind the collector on top of the furnace, hooked to the triple wall and found a bunch of holes. He quoted mt $2000 for new furnace installed and $2000 more for a new AC Compressor, installed. That includes fixing the floor around the furnace where it's rotted out.

I really appreciate you taking time from your day to help poor idiots like me out. I have told several people about your site, keep up the great work. Thanks again, Rick

Hi Rick,

Thanks for update, sometimes the hvac tech route proves best for real, huh ?

You're very welcome, happy to help.

Thanks for the support, the site, online store and MH Parts Store is owned by Mark Bower.

I'm a moderator for the hvac forums and am an employee there and through private emails and parts sales from online and public stores.

I also run service/repair calls aside from this, so do stay pretty busy.


Take care and best wishes,
Robert