Furnace (non) operation

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Furnace (non) operation

August 25, 2010, 11:34:07 am

Since I bought this in Phoenix, who knows when it last ran. I fiddled with the thermostat and finally the blower came on, but it never tried to light, and the blower just kept running. I did the carbon monoxide/LP detector tests, and the water heater and burners work so I'm assuming the lack of propane isn't a problem. The valve switch on the furnace itself is in the on position and the breaker is in. Anything else I can check before taking it to the shop?

Re: Furnace (non) operation

Reply #1 – August 25, 2010, 12:14:22 pm

Quote

I fiddled with the thermostat and finally the blower came on, but it never tried to light, and the blower just kept running.
Anything else I can check before taking it to the shop?

A few resources that might help:
http://www.marksrv.com/furnace_trouble_shooting.htm

http://www.rvmechanic.com/current_category.181/Forum.21957/offset.1290/forum_thread_full.html

http://www.rverscorner.com/articles/furnace1.html

Re: Furnace (non) operation

Reply #2 – August 25, 2010, 01:06:17 pm

I presume you have two furnaces. Does neither furnace light? If you have one that does light and another that does not it may be a thermocouple. If your furnace is like mine, there is a thermocouple under the furnace cover and under the flame shield that goes bad frequently. It looks kind of like a diode, acts like a fuse and is connected with a brown wire as I recall. Use a continuity tester to see if the thermocouple conducts electricity on both sides. If not, they are readily available at the RV store. Just unplug the old one and take it with you for comparison.

If both furnaces don't light, it still could be the thermocouples but it is less likely. I also had an issue where a mouse got into my coach and chewed a wire between the thermostat and the furnace. That took weeks of looking before I found it so if you not totally anal like I am and you don't have the patience of job, take it to an RV repairman if you can't zero in on the problem. Take you checkbook too.

Re: Furnace (non) operation

Reply #3 – August 25, 2010, 01:19:31 pm

I suggest that you remove the thermostat from the wall and give it a good cleaning with an electronic cleaner spray or ether to get rid of any accumulated crud. Then, run a piece of rough paper or contact burnisher between the contacts on the spring, and also clean between the contacts where the main switch is on the bottom left corner. Contamination in either of these places will cause operational problems.
After that, if it still doesn't start, check the 12 volt source at the furnace and make sure you have at least 12.5 volts. The motor sail switch will not activate if there isn't adequate voltage to spin the blower fan fast enough. Listen to the fan motor as the motor may have all the lubricant in the bearing dried up. If it ever screams, replace it, and you WILL hear it, if it screams. There are other switches in the furnace that can also cause problems which you can replace, if you are handy. You will need some LONG Allen wrenches to get the motor and fan out. Not rocket science but every thing is crowded into a small space and it can be frustrating. Good Luckl
Regards,

Re: Furnace (non) operation

Reply #4 – August 25, 2010, 03:25:01 pm

No, only one furnace. Since I had to "fiddle" with the thermostat to even get the fan to run I think that's a good place to start. I take it it's not unusual for the fan to keep running even if no ignition?

Re: Furnace (non) operation

Reply #5 – August 25, 2010, 06:12:29 pm

No, that is NOT unusual.Regards,
JON TWORK KB8RSA

Re: Furnace (non) operation

Reply #6 – August 25, 2010, 10:32:42 pm

I would guess the most probable problem is the circuit board connection. It's easy to clean. The single edge connector gets fouled with minor oxidation. Open the outside door, then the inner black plastic door and the connector is on the left. Just plugging it in and out a few times can do the trick. As a preventative measure add a thin coat of dielectric grease to the board contacts.

Re: Furnace (non) operation

Reply #7 – August 26, 2010, 08:49:19 am

John, please educate me. I have seen dielectric grease recommended several times to prevent future corrosion on electrical connections. Why use a non-conductive grease? It seems you would want a lubricant that conducts electricity.

Re: Furnace (non) operation

Reply #8 – August 26, 2010, 08:57:26 am

Quote from: Kent Speers – August 26, 2010, 08:49:19 am

Why use a non-conductive grease? It seems you would want a lubricant that conducts electricity.

Conductive grease would act as an electrolyte solution (think of electroplating). Electrons would migrate through the grease, cause corrosion, and could also lead to shorting.

-M

Re: Furnace (non) operation

Reply #9 – August 26, 2010, 09:37:52 am

Thanks for the input but I'm not sure I agree with using dielectric grease on metallic electrical connections. It seems that the non-conductive grease could interfere with the flow of current and could cause failure or an increase in the resistance of the wire or connector. In this case it could affect a circuit boards performance. In my past life in business, we used dielectric grease to lubricate rubber or silicon insulation around connectors but we did not apply it to the connection itself.

I'm probably nit picking but thought I would share my experience. Remember, my comments are worth every penny they cost the forum, Nada.

Re: Furnace (non) operation

Reply #10 – August 26, 2010, 09:41:28 am

Its purpose is to keep moisture off and prevent corrosion.

Contacts squeeze it out of the way when a plug is inserted.

best, paul
___

best, paul
"Thriving not surviving" <(*¿*)>
Paul Schaye (at 2008 NYC Marathon)
See our blog at LazyDazers.com

Quote

John, please educate me. I have seen dielectric grease recommended several times to prevent future corrosion on electrical connections. Why use a non-conductive grease? It seems you would want a lubricant that conducts electricity.

Re: Furnace (non) operation

Reply #11 – August 26, 2010, 10:54:14 am

And the answer is........the thermostat. I'll just look into a new one, they can't be that expensive.

Re: Furnace (non) operation

Reply #12 – August 26, 2010, 11:17:40 am

Quote from: Gayland Baasch – August 26, 2010, 10:54:14 am

And the answer is........the thermostat. I'll just look into a new one, they can't be that expensive.

Replace it with a Hunter electronic thermostat from Wallyworld. They work great. Do a search over on RV.net for the instructions. You can also use it to control the A/C.

But I think you should pull the circuit board from the furnace and clean up the connections. Just use a eraser on the end of a pencil to clean them up. That is often the big problem with our furnaces.

Re: Furnace (non) operation

Reply #13 – August 26, 2010, 12:57:27 pm

I began used dielectric grease a few months ago. I have used it on light bulb contacts, shore power connectors, small battery contacts, and toad connections. The lubricating effect seems good. It looks like there would be protections from moisture, resulting in less corrosion. On shore power connectors and toad connections, the grease with collect dirt, sand, and small debris.

I will continue to use it where protection from moisture or humidity might be an issue, but will refrain from using where it would easily collect debris.

Your post reminded me to run the furnaces and gas water heater at least once a month to verify that all works, and that the daubers haven't plugged the flues.

FOR PatC-Hunter Thermostat

Reply #14 – August 26, 2010, 08:07:48 pm

Do you happen to have a model number?
Apparently there are a LOT of different models.
Did several searches on RV.NET and got no results.
Regards,

Re: Furnace (non) operation

Reply #15 – August 26, 2010, 10:48:31 pm

I think the Hunter thermostats are like a lot of electronics and change models frequently. I don't think the brand is all that important. What I remember is that these are standard house thermostats which normally run on 24 volts AC. Many thermostats rely on this voltage to run (no batteries required because the 24 VAC comes from the furnace). The Hunters were unique in that they required two AA batteries and used relays to make contacts for control. Since our RV furnaces are are 12 volts a standard house thermostat (no batteries) would not work. To sum up, any house style thermostat that uses batteries to run should work - that's what I remember. I would be good if anyone else can confirm.

The hardest part about changing to a Hunter is figuring out the wiring. I did it by finding which wire is 12 volts (supply) and tracing out the circuit on the old thermostats and then testing. My coach has both the AC and furnace on the same thermostat. Some coaches have separate thermostats for each (I think mid 1990's due to the Coleman Penguin AC's unique ribbon cable control)

The other big advantage of the electronic thermostat (Hunter) is it controls the temperature swing much, much better - and they don't even cost much ($20 for one w/out a timed temperature function)

Re: Furnace (non) operation

Reply #16 – August 27, 2010, 02:50:40 pm

I guess I will add my two cents. I don't think the voltage makes any difference in a conventional thermostat and I am not sure it does even with an Electronic. The 24 VAC is simply the industry standard for residential furnace relays. A thermostat is just a switch that activates the relay. If it works on 24 VAC I think it should also work on 12 VDC.

If I am correct, any residential thermostat should work once you determine which wires are for heat and which wires are for AC. That can be done with the continuity function on most volt meters. If anyone knows better, please correct me.

Re: Furnace (non) operation

Reply #17 – August 27, 2010, 08:31:04 pm

This is with the A/C being controled
this link opened a security warning about the security certificate being for another site, think it was because I used RV.nets blog for the search. I opened it anyway and had no problem.https://rv.net/forum/index.cfm/fuseaction/thread/tid/23068017/gotomsg/23073058.cfm

Here is another thread:http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/24185866.cfm

And another 7 page one:
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/23070072/srt/pa/pging/1/page/1.cfm

And hopefully here is the link to the complete search for Hunter Thermostats:
http://blog.rv.net/search-results/?cx=015803640118380677498%3Av9hxss1qjcq&cof=FORID%3A11&ie=UTF-8&q=hunter+thermostat&sa=Go#1896

Re: Furnace (non) operation

Reply #18 – August 27, 2010, 08:43:01 pm

VW TDI and late model VWs have one of the most sensitive electrical systems on the market. Use dielectric grease for the glow plug connections and the mass air sensor after the air cleaner and on other critical points just to keep them working properly. If I don't do it, have all kinds of problems with those items. This was one of the tricks I learned at the TDI Club which is the VW TDI owners group. If you have a connection with someone at a Chrysler/Dodge garage, they have some of the best on the market. But don't buy the whole pail cause it cost a small fortune. Just have them fill a small container for you.

Quote from: Kent Speers – August 26, 2010, 09:37:52 am

Thanks for the input but I'm not sure I agree with using dielectric grease on metallic electrical connections. It seems that the non-conductive grease could interfere with the flow of current and could cause failure or an increase in the resistance of the wire or connector. In this case it could affect a circuit boards performance. In my past life in business, we used dielectric grease to lubricate rubber or silicon insulation around connectors but we did not apply it to the connection itself.

I'm probably nit picking but thought I would share my experience. Remember, my comments are worth every penny they cost the forum, Nada.

Re: Furnace (non) operation

Reply #19 – August 27, 2010, 09:05:50 pm

Regarding the 24 volt thermostat question - a very wise question, I was about to ask it myself! Googleing it I find several references to using 24 volts in RV's, several with the exact model I just bought, Hunter model 42995. Here is a quote from one of the RV sites:

"Just be sure the thermostat you select is battery powered. Some residential thermostats use 24 VAC to power them. But if they have the battery backup feature, they can be used for RV 12-volt systems."

Unfortunately, or maybe it doesn't matter, but I see that it's for both heating AND AC, which I don't need. Have I added complexity to the installation? My setup to the old thermostat only has two wires and I thought HA, I can do this.

I haven't opened it yet so I could return it, but they seem to all be the combination.

Re: Furnace (non) operation

Reply #20 – August 28, 2010, 10:37:05 am

Gayland, I think the issue of 12 VDC vs 24 VAC is only pertinent to digital thermostats. The digital components probably require a 24 V power source unless the thermostat has its own battery power. If your new 42995 is a mechanical model, no digital readout, it should work fine on your 12 V system even if you don't want to use the AC function. I would agree that a digital without its own battery power may not function properly.

To figure out which connections to use, make sure the thermostat is set for heat and is set higher than the ambient temperature. Look on the back of the new thermostat for a screw connector marked G for ground. Hook the black volt meter lead to that connector and the other lead to the screw marked H for heat. This should complete the circuit and make the voltmeter beep if your meter has a sound function or read 0 on the dial or digital readout. If this procedure works with your thermostat leave the volt meter connected and turn the temperature up and down to insure it will turn on and off properly. If it does, you have the points of contact for the old wires. Use your volt meter to determine which of the old wires is the ground and hook up the new thermostat accordingly.

If you new thermostat doesn't have the connections marked on the back I just wasted a lot of typing. Let me know. We can probably still work it out.

Re: Furnace (non) operation

Reply #21 – September 03, 2010, 01:55:12 pm

To bring closure to this thread. I installed the new thermostat, Hunter model 42995. Simple to do with just two wires, heating only. Furnace still wouldn't ignite although the fan came on. Finally traced it down to the 5 amp automotive fuse on the circuit board not making contact. Only way I can get it to finally make contact was to pull the fuse partially out of the holder, about 1/8 inch. I'll have to use it awhile before I fully trust it.

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