Furnace Troubleshooting (the first step)
I recently had a furnace come in- complaint was that nothing happened- no fan, no heat.. nothing.
Whenever I have a furnace problem, the first step I take is to go to the thermostat. This one had a simple heat only, mechanical thermostat. I pull the cover off, switch my multimeter leads to read amperage and hook up the leads across the thermostat terminals.
On this furnace, I immediately read a 1 - 1.4 amp draw, which dropped quickly to around .2 amps. This told me the time delay fan relay in the furnace was good (on [b]most[/b] furnaces built in the past 20 years, this will be a valid test- the exceptions will be new models with “fan control” circuit boards, or models where the board has been retrfitted with a Dinosaur brand fan control board).
After about 40 seconds, the blower came on, and the amperage rose a bit to around .5 amps. After another 45 seconds, the amperage rose again to about 1 amp.
What these readings told me was 1- the relay was good and the furnace had power (the initial high amperage reading was the heating element in the relay heating up), the second amperage jump (after the blower came up to speed) told me that the limit switch and sail switch were both OK, and power was getting through to the circuit board, the last amperage jump told me that the gas valve was getting power, and the circuit board was opening it. (A side point is that the final amperage reading- 1 amp- is the setting that the “anticipator” should be set at on mechanical thermostats).
For that job, I was lucky- the only problem was a bad connection in the thermostat- I repaired that connection and the furnace worked fine, but I hope you can use this method of troubleshooting to diagnose furnace problems (if you have a combination heat and AC thermostat, the same method can be used, but you have to find and break the correct thermostat wire to the furnace, which is usually easiest to find right at the furnace, and will nearly always be one of the two blue wires).
–Chris
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February 5th, 2007 at 3:29 am
Was having problem with no air forced coming through ducts
in bedroom. Removed furnace to clean and check for duct blockage.
Found medal tape had fallen off and was restriction flow. Fixed that
problem, cleaned fan and reinstalled furnace. Hooked everything back
up except the thermostat wired. Learned long ago to jump the wires out at
the furnace and check it before closing the compartment. Worked fine. Finished
hooking everything up and closed compartment. Turned on thermostat and NOTHING
worked. No heat, a/c or fan. Pulled the thermostat, took off the furnace
thermostat wired and hooked them together. Furnace worked. Haven’t finished trouble
shootong the thermostat yet. Long process for a solid state thermostat with a/c,
fan and furnace all on one thermostat. Even with furnace wires disconnected,a/c
and fan will not work. Seems 12 vdc comes through furnace. Any sugestions? What
little troubleshooting I have done, nothing makes sense. HELP!!!
February 5th, 2007 at 10:00 am
Hi Charles- the first thing I would look at is which wire hooked to which from the furnace to the thermostat.
One thermostat wire out of the furnace will be “hot” (+12v), and if it is not hooked to the correct thermostat lead, the thermostat will not have 12 volt power to operate.
March 24th, 2007 at 10:02 pm
I use a heat pump/propane furnace. In this weather the heat pump always works but when it is colder the propane comes on and a blue light on my colemane revcon thermostat comes on. Lately a red light has been coming on. It says emg above it. It stays on and circulates the air to keep temp stable but is just blowing air. no heat. Any ideas?
April 9th, 2007 at 3:09 pm
Hi Jean,
I hate to say it, but I am unfamiliar with that type of thermostat in an RV, and cannot find any information about it on the Coleman website (or in my service documents).
– Chris
September 9th, 2007 at 7:18 pm
HI CRIS,
I HAVE A Coleman THERMOSTAT WITH A 2 AMP FUSE THAT BLOWS ABOUT IN ABOUT 5TO 10SECONDS AFTER THE FURNACE FAN 12 VOLT MOTOR STARTS.IT IS NOT CONNECTED DIRECTLY TO THE BATTERY. THIS THERMOSTAT ALSO WORKS THE AC WHICH WORKS FINE.ANY IDEAS AS TO WHATS BLOWING THE FUSE?? THIS IN AN RV. THE FURNACE IS A EXCALIBUR 8500
BOB
October 19th, 2007 at 12:38 pm
My father-in-law has a 37′5th wheel forgot the model? but it has a sububan lp furnace.We had it going and worked well but after we brought it to his lot now the pilot would not stay lit.After some investigating found a bees nest in the exhaust.We pulled it out with a bent clothes hanger then blew it out with air.Now it wont stay lit at all
November 11th, 2007 at 6:34 pm
Hello,
My propane furnace will not keep the pilot light lit after it is finished running. It will make a click sound and the pilot will go out. I just changed the thermocouple two days ago and it did not solve the problem. Any insight will be greatly appreciated. Thanks,
Jeffrey
November 14th, 2007 at 5:35 pm
Hi Jeffrey,
A couple of things to check- the pilot assembly may need to be cleaned, and sometimes if the pilot is set too high, it will starve for oxygen just after the burner shuts off, and go out. The flame should *just* envelope the end of the thermocouple.
But.. in some furnaces it is near impossible to actually see the pilot flame.
– Chris
November 15th, 2007 at 2:03 pm
I’ve got an old Coleman 4225A furnace in a 1976 Winnie. Was running great until this fall(deer season). It is burning very rich, soot coming out of exhaust and too hot in heat exchanger. Pulled unit to check for any blockage or obstructions. None found. Both fans working well, just replaced the motor two years ago. Can’t adjust for a good blue flame as before. Very tall flame too tall, which starts out blue but too much yellow. Could it be an air leak or has the General Control 4225A809 gas valve gone bad? Gas stove and frig work okay, which I think leaves out main gas regulator.
November 15th, 2007 at 7:35 pm
Hi Joe,
Generally that is sign of either too much fuel or too little air. Did it run OK after the motor change? If the motor was running backwards, it would still work, but not put enough airflow through. Likewise the combustion blower wheel could be installed wrong.
If I recall correctly, that unit has a cast iron burner- the slots in those burners are very prone to blockage by rust, which blocks the air flow as well.
–Chris
November 16th, 2007 at 1:24 pm
Thanks Chris.
The unit ran fine after the motor change out, good clean blue normal size flame on all three burner sections. It does have a cast iron burner. I’ll check for blockage there. The only other thing is can I still get a gas control valve for this unit or will I have to replace the furnace?
November 17th, 2007 at 7:41 pm
Hi Joe,
I really don’t think the gas valve is the problem- I would bet on the slots in the burner being plugged up.
It’s been a while since I services one of these, but I *think* that the slots are wide enough that they can be cleaned with a hack saw blade- you don’t want to make the larger, just clean them out.
– Chris
November 19th, 2007 at 7:33 am
Thanks Chris,
You were right on the slots being clogged. I remember cleaning them out when I replaced the motor. Unfortunately when I put the unit back together, the pilot won’t stay lit so I’m getting a new thermocouple today; hoping to fix all my problems. As for the valve, I was told that they are no longer available. I just wanted to know if I could still get one.
November 29th, 2007 at 9:31 am
I HAVE A WALL FURNACE AND A MECHANICAL THEMOSTAT. I CAN’T GET MY THEMOSTAT
TO COME ON. I CAN GET THE WALL FURNACE ON BY JUMPING IT. I CONNECTED A HOT
WIRE TO ONE OF THE PLACES WHERE I JUMP IT AT AND WHEN I DO THIS THE THEMOSTAT
WON’T TURN OFF. I HAVE TO GO BACK TO MY WALL FURNACE AND DISCONNECT THE
HOT WIRE FROM WHERE I JUMP IT AT TO TURN IT ON. MY THEMOSTAT IS A MECHANICAL
ONE WITH MERCURY. CAN YOU HELP ME OUT WITH THIS PROBLEM. I NEED TO BE ABLE
TO TURN MY THEMOSTAT OFF AND ON WHEN I WANT TO AND IF WANTED TO LEAVE IT
ON THEN I COULD ALSO AND NOT WORRY ABOUT IT. I JUST WANT IT TO WORK RIGHT.
ANY SUGGESTIONS WOULD BE GREATLY APPRECIATED VERY MUCH.
THANK YOU VERY MUCH. I WAIT TO HEAR FROM YOU.
SINCERELY,
MARGARET,
mchwalowski@yahoo.com
November 30th, 2007 at 8:01 pm
Hi Margaret,
I guess the easiest thing would be to replace the thermostat, but you might take the cover off and look for a small adjustment called an anticipator- which will be a wire with a slide connector on it. Sometimes they are a round assembly, sometimes they are straight. If you move the slider down to zero, often that will “fix” a problem like that (the wire sometimes gets corroded, and moving the adjustment can help.
To replace it, a popular replacement is the Hunter model 42995, which is available at WalMart for about $20. It is an electronic model, but will work fine for furnace only- just hook the 2 wires to the RH and W terminals.
–Chris
December 3rd, 2007 at 8:38 pm
Hello, I have an Excalibur Hydroflame 8500 IV which seems to have lost it’s muscle. Everything works fine as it always has - with the exception that it doesn’t seem to heat my bus up like it used to without consuming excessive amounts of propane. I think that the flame must not be hot enough anymore but I can’t see it from any angle inside or out, I can however hear the difference if that makes sense? Every winter (this is the 5th) I acclimate to the familiar “tiger torch roar” but it is a sub-sound under the blower motor this year. Plus the air just doesn’t feel as hot as it used to coming out. From my RV repair books I think the burner/flame has issues but they don’t show how to get at the burner of this model, nor does the 3 page Atwood installation manual. Is there an easy way to determine if this is the problem? I live in the bus so leaving it at a shop is out of the question - and pulling the furnace out would have to happen while it’s snowing because it won’t be warming up here again until May… Thank you for any suggestions or directions on how to see or clean or adjust my Hydroflames Flames!
December 6th, 2007 at 1:12 pm
Hi, I have a Coleman [High efficiency gas-fired furnaces tubular heat exchanger series Model: P*UR / G9T-UP/ FG9-up (upflow) 40 - 140 MBH input] and it seems that our furnace turns on, but shuts off after 1 or 2 minutes of heating. it seems to give 6 red flashes when i check the furnace control dignostics, and in the manual it seems that 6 red flashes mean, the pressure switch opened 4 times during the call for heat?? and we have no idea what they mean by delay on or off mode. can you help me with this problem?
Sincerely James
December 11th, 2007 at 4:04 pm
I have an older Lennox forced-air furnace with a standing pilot. For days the pilot would randomly go out. I replaced the thermocouple, cleaned the orifice, and ajusted the small hood on the pilot flame opening.
The thermocouple it sitting nicely in a strong blue flame, and once the pilot is lit it will stay lit for five or so minutes and then you can hear the solenoid release the gas valve and it closes. End of pilot.
Any idea what this problem might be? When the furnace runs, it runs well. The gas valve just won’t stay open to keep the pilot going. I hope it’s not the gas valve.
Thanks!
Regards,
Michael
December 11th, 2007 at 4:17 pm
Hi James,
I’m afraid I don’t have any service information (or, for that matter, any experience ;)) with home type furnaces.
But.. Michael- I would almost be tempted to replace the thermocouple again, as I have seen brand new thermocouples fail. They wrok using two different metals, which generate current when heated, but every now and then the junction between these metals can open up when heated.
– Chris
December 11th, 2007 at 4:57 pm
Thanks Chris. I’ll try that. Ggrrr.
December 11th, 2007 at 6:15 pm
Hi Michael,
One more thought- the connection of the thermocouple at the valve is actually an electrical connection- if you look at the end, the very tip is insulated from the outside of the tube by a thin insulator.
The thermocouple should be hand tightened firmly, plus a quarter turn- if the pilot doesn’t stay lit, give it another quarter turn. Over tightening can crush the small insulator.
– Chris
December 17th, 2007 at 3:39 pm
Hey Chris,
Just bought a used RV, suburbane furnace. have got it to light off twice in two weeks of trying every day, 6-7 times a day. Removed furnace, removed board took it to RV repair shop, board tested ok. I get fan, I get spark, just not lighting the pilot.
December 30th, 2007 at 5:22 pm
I have a Suburban SF-30 in an Outback 33′ that is 1.5 years old and on it’s second cool season. It always seemed to a little temperamental when igniting but has generally been trouble free. Today, not so. Everything starts and runs but no ignition takes place. Coincidentally, I had a tank switchover take place about the same time it quit. The switchover appeared to be normal as I have gas at the stove, frig, and hot water heater. I broke the line at the heater and have it there as well. Both tanks share a common regulator on the output of the switch. As for correct pressure, I don’t have a manometer but judging from the stove burners, it looks okay. ( Side question, just how much of a pressure drop can a furnace stand before it refuses to work??) Could the switchover have starved the furnace and damaged a gas valve or something? Because of it’s location, it appears that it has to be completely removed to service the components so I don’t want to do that unless absolutely necessary. Any input to a possible solution would be appreciated. Thanks.
January 2nd, 2008 at 11:59 pm
I have the exact situation as Kenny above blower blows plenty of propane, igniter tries three times but will not fire furnace. Please comment, ASAP I’m getting cold.
thanks,
rick
January 3rd, 2008 at 9:50 pm
Well let’s make that 3 of us, I have 05 TT with a Suburban sf30f, stove work great, blower comes on then 3 or 4 popping sounds then the blower shuts off(this is in about 10 time span)…I going to wally world and buy a radiator heater
January 6th, 2008 at 10:55 pm
Make that four of us. I have a Suburban furnace that’s be working intermittently. Now it won’t work correctly. The fan comes on, I hear the igniter, smell the propane, but no ignition.
January 7th, 2008 at 3:23 am
For the guys up above:
Unlikely this could help all of you but may be of help so I offer it up - I had a similar problem with my furnace last year that was due to an overfilled propane tank. Electronic lockout can occur if the gas pressure coming is too high, it’s a built in safety feature. Another similar situation my first year way back was flies and spiders camping on the burner - they clog the combustion process - after I got it lit a dozen times or so (each time it stayed on a few seconds longer) they were burnt off and I had no problems.
Good Luck!
January 7th, 2008 at 10:24 am
FurnaceGirl,
Thanks, but no bugs in the burner and I’ve tried with two different propane tanks - one about 1/5 full and the other full (well, “OPD” full).
January 8th, 2008 at 6:38 pm
I have a 8500-iv hydro flame seies furnace in my 2003 Toy hauler.I have trouble shot to the best of my knowledge,the blower works,electrode works,but no power from ignition board to valve.also after electrode stops trying, red light on ignition board comes on.Any help would be appreciated.
Thanks,
John
January 9th, 2008 at 3:05 pm
Sounds like your board may have died - common problem, not too hard to fix. Go here and search your model number for T-shooting and repair help.
Cheers (-:
January 17th, 2008 at 1:22 pm
i have a Suburban model NT-34L furnace. initial problem was a popping sound each time the burner lit. As i sleep with my head over the furnace, this got to be old in a hurry. I initially replaced the gasket around the burner access thinking that an air leak might cause the popping. still popped. I pulled the furnace, cleaned the blowers (intake and exhaust), removed the mud dauber nests, removed the burner and cleaned it as it 4 slots blocked with rust. reassembled furnace, reinstalled and guess what- furnace still pops upon ignition. It also will pop intermittantly if i let the furnace run. Gas flame is blue, some orange/yellow above the burner, flame kind of ripples right on the cast iron burner. no separation between flame and burner. Please advise and thank you.
February 16th, 2008 at 2:16 pm
Sounds like we may all have a similar problem. I have a Suburban N-30M furnace with the same problem as mentioned above. Solenoid energizes but propane is not flowing. I replaced the solenoid valve.. still not working. Tested ewverything on the bench and found that the solenoid although clicking when powered, is not allowing flow when energized under pressure. If solenoid is energized and then the propane is thurned on, I get flow. Confused as to why this is happening. I even tried botha 20psi and 10psi propane regulator. Any suggestions would be appreciated.
February 16th, 2008 at 3:54 pm
I found the answer to the post I made previously. The unit had been dropped off at my house by a friend who couldn’t fix it. I replaced the transformer and then ran into this “propane flow problem”. It seams he connected a supply line/regulator he had laying around to test the unit. This regulator was for 20 psi. Some research showed that the solenoid is only rated for 1.5 PSI. The hard piped line in the camper is regulated at this lower pressure and everything now works fine.
February 27th, 2008 at 4:46 pm
Chris,
My furnace blower fan just stopped working today. I tried/tested the furnace a couple more times with the thermostat igniting the furnacw with natural gas burning fine—just no blower fan. is the problem most likely a fan motor gone out or could it be something else.
February 27th, 2008 at 7:54 pm
Jack,
Is this furnace an RV furnace? The only reason I ask is that in new RV furnaces, the burner cannot ignite until the blower is running.
If it’s a house type furnace- I’m not that familiar with them, but usually the blower is controlled by a fan switch, which turns the blower on when the heat chamber reaches a set temperature.
If it’s an RV furnace, I would suspect the fan relay.
March 4th, 2008 at 11:00 am
I finally got the step working after another cleaning of the
large 4 way plug and the door switch. It seems to stay out now.
Thanks for the input.
March 4th, 2008 at 10:46 pm
I have a rudd furnece and it will be runing then it seems like a air pocket in the gass line and then theres 3 or 4 sucksons then the furnece shuts off then you here clicks then it starts back up right away and will stay runing and it will do this every now and then can you please help me thanks mike
March 16th, 2008 at 9:28 pm
Hello:
I have a Suburban SF-20F and nothing happens. No blower no clicking nothing and its just past the warantee. I checked that it is getting power and the power is there. The thermostat is putting out voltage when I switch it to the heat setting. I was going to bypass the control module and put the hot wire right to the blower but I dont want to try things without some advice. Thanks for any help!!!
Steve
April 3rd, 2008 at 12:14 am
I have a Suburban floor furnace in our 1992 Sandpiper. It has electronic ignition. When I turn the thermostat on the fan comes on and only blows cold air. I have been told this might be the thermostat but I do not know how to test it. Can anyone help. Thanks
April 3rd, 2008 at 5:38 pm
I wish that I would have found these posts before I tryed to fix my Suburban SF-30F furnace. The theromstat would start the fan, but there was no burner ignition. I removed the furnace. I took the burner apart and cleaned out the sand. I re-set the ignitor gap to 1/8 inch per the manual. After trying many different things, I jumpered the two blue thermostat wires instead of hooking up the thermostat. Then the furnace would start and light every time! Maybe a bad thermostat? I hooked up the thermostat again and found that the voltage to the limit switch was 7 to 8 VDC even when my converter was putting out 13.6 VDC, which is normal. I found a loose rivet in the Suburban thermostat, which I soldered (this can melt the plastic).
This fixed the problem, but I still couldn’t explain why the thermostat was only getting 11 VDC when the furnace was running (10 VDC at the limit switch. I found a two volt drop on the positive power wire to the furnace, but only 0.25 volt drop on the ground return wire. I replace the power two wires with about 10 feet of # 14 wire so the furnace now runs at full voltage.
April 4th, 2008 at 11:54 pm
In my ‘04 Arctic Fox 24-5N, there resides a Suburban Furnace. It heats the
5th very well and will be 5 years old in July.
Since this is my first experience out of a tent or house, I thought my
furnace was working properly all along, till late last year. That is when
the steps in the furnace’s processes changed and made me think it may have
been busted from the get-go.
With the thermostat set at a temp higher than the room temp, I switch the
thermostat from ‘off’ to ‘heat’. Here are the steps the furnace took the
first 4 1/2 years;
1. Instantly, the blower motor comes on. You can feel the air blow out the
heater outlets in the floor.
2. It heats the trailer very well and when it reaches the thermostat temp,
the gas turns off and the blower continues to run.
3. The blower runs for about 2 min. (I understand this to be the ‘cooling
down’ time so the furnace doesn’t stop hot) At the end of this 2 min, the
blower power goes off and the blower begins to wind down.
4. Before the blower stops, it kicks back on and runs for another 2 min, at
the end of which, it powers down.
5. Before the blower stops, it kicks back on AGAIN and runs for another 2
min at the end of which, it powers down and stops.
6. The heater is off, waiting for the thermostat to tell it to turn on
again.
What changed to make me think this wasn’t normal?
Sometimes, the heater will skip steps 4 and 5, or will repeat step 4 several
times. The heater will cycle at least once, mostly 3 times, but up to 7
times (that I know of). The air is blowing room temperature after the 1st or
2nd cycle.
Relay???
April 5th, 2008 at 8:08 am
Hi FMB-
I would guess that the furnace has been cycling on the limit switch- the thermostat is still calling for heat, but the furnace is getting to hot, shutting off and then cooling down and reigniting.This is usually caused by not enough ductwork or a disconnected duct pulling hot air back in to the intake.
Given that yours has changed, I would guess that it was not enough ducts, and one may have split open- or you had a register that was closed that is now open.
Sorry about that- I went and reread your post- it does sound like the relay- I’m assuming that you don’t have one of the newer models with the fan relay on the circuit board.
Steve P- if you have a heat only thermostat , which only works the furnace, you can just take the wires off the thermostat and hook them together- the thermostat is simply an on/off switch.
–Chris
April 10th, 2008 at 12:29 am
Chris, thanks for the reply. It is a SF30F and I don’t see a relay in the Installation instruction manual diagrams so I’m thinking it might be integral to the circuit board. I will have to pull the furnace out to determin that.
Oh, wow. Am I glad you only struck through and didn’t delete your first comments. I always thought the bathroom floor vent didn’t blow much and the bedroom vent blew less (barely felt air move). I took the cover off to measure voltage on either side of the Hot limit switch and it dawned on me the amount of air blowing with the front cover off was enormous. With the cover off heater on, the blower sends copious amounts of heated air into the room through where the cover and cabinet intake vent would have been. When it came time to turn off, it went through a ~2 min cycle and turned off. I repeated this several times. With the covers on, it cycled 3-5 times. Hmmmm…. plugged vent tubing somewhere I’m guessing now, cause when I remove the vents out of the system, the heater works fine. Back to looking at vent tubing tomorrow. Thanks.
April 23rd, 2008 at 10:47 am
I have a Suburban furnace in a ‘87 Winnebago.
It worked fine until the day I needed it and then
nothing. Any suggestions where to look first?
May 7th, 2008 at 10:42 pm
I need some help! I have an Atwood Mobile Products Furnace in an 04 Bayhauler Trailer. (Mod # 8520-IV-DCLP) The wall Thermostat control is a Duo-Therm by Dometic. The furnace kicks on, ignites and blows hot air, unfortunately it si for a very short peroid of time. The heater will blow for a few minutes and shut off. The camper never gets warm. The heater has worked fine and now all of the sudden isn’t working right. He have taken the inside and outside cover off and blown air around to see if it could be dirty. Any suggestions?
Thanks- if you can help it would be great it sure is cold in Wyoming!
May 9th, 2008 at 2:58 pm
I have 86 winnie motorhome with Atwood 7912 Hydro Flame,blower(fan)runs continuously when thermostat is turn, on but no ignition(flame),gas is on,would you give me a step by step run down so I can find and correct the problem? Thanks Rod.
May 20th, 2008 at 8:32 pm
Chris: Have a Suburban SF-35F furnace in an 05 Hornet Retreat. Has worked fine for the last 3 years until last weekend. Turned furnace to Heat and instead of the blower coming on and running for 30 seconds to 1 minute before igniting all we got was a buzzing noise coming from the furnace. Turned furnace off and buzzing noise remained until approximately 1-2 minutes before buzzing noise turned off…almost like a blower cycle time. Waited about 30 minutes, turned back on, same buzzing noise occurred. Pulled furnace out, and with switch in heat mode buzzing noise occurred and noticed blower fan moving very slowly. Tried it the next weekend to see if there was any difference, furnace did nothing, no buzzing, no blower, nothing. Any ideas?
May 21st, 2008 at 2:02 pm
Hi Doug,
It sounds like either the blower motor or the fan relay. I would hook 12 volt power directly to the blower motor to see if it will run OK (make sure the blower will turn freely, as well).
If the furnace has the outside door, you should be able to do this without pulling the furnace out (IIRC).
May 21st, 2008 at 5:40 pm
Follow-up: Is the relay inside the furnace by the blower motor? No access door from the outside. Will there be 2 wires on the blower motor that I can hook 12v to, and is the white wire the ground on the furnace also?
May 23rd, 2008 at 10:10 pm
i have a wall furnace(no idea what the make is) and it is controlled by a wall thermostat. it started to make a popping sound and than a ball of fire would come out from the grill. turned it off and cleaned it up, called the gas co and they said to let the dust burn. turned it on after it had burned clean and it popped and fire came through again. we have been using it for the past 7 years and never had this occur before. any idea what it could be? thanks
June 1st, 2008 at 10:12 pm
Chris,
I have a Suburban furnace in my 01 Sierra. I have had an ongoing issue with the furnace that is frustrating me big time.
With fully charged batteries my furnace will run 2/3 through the night before it stops igniting and the fan runs cold. Last year my converter went on the fritz and I figured it wasn’t charging the batteries good enough. This year I installed a PD power distro center with the charge wizard. I still get the same result from my furnace. If I plug my truck into the trailer the furnace will run all night but if it runs off my batteries alone it will stop 2/3 through the night. I have two deep cycle batteries that load test really well and through all this the lights in my trailer never go dim so batteries are not on my list.
What is going on??
I replaced the blower motor
June 1st, 2008 at 10:15 pm
Continued:
I replaced the motor in my furnace, it was dirty and the bearings were rough. I figured this was my issue but it is not.
June 2nd, 2008 at 8:33 am
Hi Doug,
I would bet that there is a voltage drop somewhere in the system- probably several, so even when the batteries are still up, the voltage to the circuit board gets low enough that it will not operate correctly.
*If* the wall thermostat only works the furnace (and not the rooftop air conditioner), I would start there, but I’ve seen a lot of limit switches (which you access by removing the inside cover) with enough oxidation to severly drop the voltage- as well as the sail switch.
June 2nd, 2008 at 8:54 pm
My thermostat does control the rooftop A/C and the furnace. So I start by inspecting the limit switch(inside the furnace) and then the sail switch. What would the normal voltage drop across these components be?
Is it safe to say seeing how the system works with the truck hooked up that the circuit board is OK?
June 2nd, 2008 at 8:58 pm
My thermostat does control the rooftop A/C as well. I guess I will test the sail switch and the limit switch for voltage drops, what would you say is maximum acceptable across both these components?
Is it safe to say my circuit board is operational with no issues or may I have an issue there?