Yet another furnace question

[turbojimmy]

I've read a lot of threads on furnaces, but haven't come across one like this. Naturally the furnace worked fine last winter, but now that I'm actually camping in the RV it's decided to act up.

It will work normally every time on a cold start up. Fan runs for a bit, ignition fires, warmth ensues, it shuts off when it reaches the desired temp. The issue is when it restarts.

It first started doing it last weekend. In the middle of the night it felt cold. I heard the furnace "click" when the thermostat called for heat, but it didn't do anything. After shutting it off and turning it back on with the ON/OFF switch at the T-stat it fired up and was fine for the rest of the night.

This morning, however, it wouldn't fire up. I would shut it off and turn it back on, hear it click, but no fan.

I took the cover off and spun the fan with a long screwdriver. It seemed okay. I then turned it back on. The fan ran for less than a second. Shut off. It tried again by itself - fan ran for less than a second, shut off. I shut the switch off and turned it back on. It did the same thing. On the third try the fan ran as it should, burner fired up and we were off to the races.

So....failing fain?

[turbojimmy]

I swear this thing is possessed. I work from home a good chunk of the time, so I set my "office" up in the RV out in the driveway. When I'm in it, the furnace cycles on and off exactly as it should. All day long now.

But when I'm not in it, it gets ice cold until I cycle the thermostat a few times and the fan finally continues to run.

To be continued.....

[turbojimmy]

enblethen wrote:
An 84 rig should have a remote time delay relay which would start fan before power goes to the circuit board via the sail switch and thermal cutout. That would or should eliminate circuit board as primary problem.

I'm thinking this might be the problem. The thermostat is doing what it should. Something "clicks" loudly at the furnace, but I get nothing fan-wise. If I turn the thermostat down, and then back up (sometimes 2 or 3 times) it will function as normal until it needs to fire again.

The 24k BTU furnace in the rear is trying to pick up all the slack, which is not working.

[turbojimmy]

It started misbehaving again.

It's an NT-30S unit (30k BTU). In searching for a serial number, I noticed that it had been disassembled before. The fan is new, as is the control board. The control board is hanging from its wires - not even installed properly. So I think maybe someone was trying to solve a fan problem before I owned it.

A new board is only around $80.

I'm going to take it apart, check the connections and mount the board properly. Maybe that will fix it for now.....

[turbojimmy]

nomad297 wrote:
Did you get it figured out?

Bruce

Not really. It magically started working again. It ran all night Saturday without any problems. I don't know if it's worn windings on the motor or something else, but apparently a little exercise got it going again.

[nomad297]

Did you get it figured out?

Bruce

[RayChez]

Sounds to me like the fan motor is about to quit working.

[turbojimmy]

I haven't tried any of your suggestions yet, but I do appreciate them.

I stayed at a local campground last night. It got down into the 30s. Both furnaces worked fine. The front one, the one that had been acting up, ran nearly non-stop but when it did shut down it fired up again like it was supposed to. I don't know if it needed exercise or what. If/when it acts up again, I'll check the thermostat.

[path1]

Bypass the t-stat with piece of wire to make sure t-stat works before digging into further.

Check for loose connection to thermostat or system and clean contact points on t-stat.


My old mechanical t-stat likes clean contact points.

If t-stat is problem, before buying a new t-sat clean up the contact points one of two ways.

1. Remember exactly "anticipator" is before doing any cleaning. So you can put back in exact place, just in case you do move it.


2. "burnish" with stiff piece of paper (index card, match book cover etc)

3. If t-stat contacts has little nipple thing that you can't burnish without destroying nipple use a elec contact cleaner http://www.amazon.com/gp/product/B000BXOGNI/ref=pd_lpo_sbs_dp_ss_2?pf_rd_p=1944687682&pf_rd_s=lpo-to... or if nobody is looking I use "brake clean" from any auto part store, just a tab of spray on a Q-tip to clean.

[enblethen]

An 84 rig should have a remote time delay relay which would start fan before power goes to the circuit board via the sail switch and thermal cutout. That would or should eliminate circuit board as primary problem.

[Grandpere]

My guess is that it is the control board getting ready to go bad. It is going into lockout mode, and that is controlled by the control board. It could be the propane switch, but being mechanical they usually do not fail, if they do, it usually is an all or nothing type of thing. Ours did something similar and finally would not go into lockout mode, the fan just ran all the time. I have a new board ordered and it should be here next week. I got it from American RV, the least expensive place for parts that I have found.

Russ

[Sully2]

You need an RV furnace tech!

[enblethen]

The fan should run even with a bad sail switch or thermal cutout.
I would test the thermostat.
Remove the cover, locate the two wires going to the furnace. Connect them together. Fan should start, furnace should ignite and produce heat if 10-15 seconds. Run furnace in this mode for a few minutes. Separate the two wires, furnace should go into cool down mode and shut off in 15-30 seconds.

[turbojimmy]

rgatijnet1 wrote:
Sounds more like a failing switch/control board.

Any guess around which switch? There's 2 right - sail and high-temp cut out?

And...I'll pull the fuse just for fun to see if it clears up.

It's a 1984 vintage furnace, but I can tell the guts have been out of the case and replaced. Despite it's age, it is electronic.

[nomad297]

Pull any 12 volt fuses related to your furnace, wait for a minute or so, then put them back in. I don't know if this will work, but this procedure has "fixed" several problems with electronics over the years. In fact, it just worked for my friend who was having a problem with his brand new Norcold four door refrigerator.

Bruce