Forum Discussion

turbojimmy's avatar
turbojimmy
Explorer
Oct 11, 2014

Yet another furnace question

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?
Class A
  • turbojimmy's avatar
    turbojimmy
    Explorer
    Oct 24, 2014
    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's avatar
    turbojimmy
    Explorer
    Oct 24, 2014
    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's avatar
    turbojimmy
    Explorer
    Oct 23, 2014
    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's avatar
    turbojimmy
    Explorer
    Oct 13, 2014
    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.
  • turbojimmy's avatar
    turbojimmy
    Explorer
    Oct 12, 2014
    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's avatar
    path1
    Explorer
    Oct 11, 2014
    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-top-stripe-1&pf_rd_t=201&pf_rd_i=B003NTQCA2&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=1Z7S124V0C9CDJXZB366 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's avatar
    enblethen
    Nomad
    Oct 11, 2014
    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's avatar
    Grandpere
    Explorer
    Oct 11, 2014
    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

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