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Old 04-22-2010, 09:39 PM   #1
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converter problem?

I have another thread on here about my Suburban furnace. I picked up the rig from the repair shop and was told that the circuit board tested fine, and all wires and connections were good, and the furnace ran every time they tried.

I was talking to the salesman, and he suggested maybe I have a bad converter. He says they tested the furnace on battery power only, and a fully charged battery was supplying the proper voltage. He theorizes that when I was plugged into shore power, making the converter power the furnace, if the voltage is too low coming from the converter the furnace blower won't start thereby stopping the furnace from running. Kinda makes sense to me. Does this theory hold any water? By the way, the converter is a WFCO WF-8900 series three stage converter according to the manual.
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Old 04-22-2010, 10:17 PM   #2
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I don't follow the salesman, but he may know something about your RV that's not common. For most RV's the batteries never leave the 12V circuit, they are in series and all 12V power comes through them.

Are you able to fire the furnace without being plugged into shore power, but not when you plug in? I wonder if they tested with their batteries, instead of yours. My 1st guess is that your batteries are failing and can't supply enough amps regardless of the RV being on shore power.

This site has a wealth of 12V info that may help you troubleshoot:

http://www.ccis.com/home/mnemeth/12volt/12volt.htm
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Old 04-22-2010, 10:32 PM   #3
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Originally Posted by grandpaofthree View Post
I have another thread on here about my Suburban furnace. I picked up the rig from the repair shop and was told that the circuit board tested fine, and all wires and connections were good, and the furnace ran every time they tried.

I was talking to the salesman, and he suggested maybe I have a bad converter. He says they tested the furnace on battery power only, and a fully charged battery was supplying the proper voltage. He theorizes that when I was plugged into shore power, making the converter power the furnace, if the voltage is too low coming from the converter the furnace blower won't start thereby stopping the furnace from running. Kinda makes sense to me. Does this theory hold any water? By the way, the converter is a WFCO WF-8900 series three stage converter according to the manual.
Grandpa. Furnaces have an air flow switch (sail switch) which senses that the main blower is running at a sufficient air flow to opperate. If it is then the rest of the ignition and run sequence will follow. If the switch does not have enough air flow to activate then the furnace will continue to run the blower for a set amount of time then shut down. Many older furnaces would just let the blower run until your batteries were dead. Newer furnaces will try the start sequence usually 3 times before they will "lockout" and the furnace will not come on again until it is reset by removing power.

Most all RV apliance circuit boards will not run at voltages under 10.4 volts.

You can test your converter/charger by plugging in your coach and then using a volt meter test the voltage at the batteries. You should have between 13.2 and 13.6 volts if the converter is functioning correctly. If you don't get that then something is wrong. You should also check the water level in all your batteries at least once a month if you leave the rig plugged in. Most converters in RVs are 2 stage and will just cook your batteries instead of maintaining them. WFCO builds a good converter/charger but I can't tell you without a little research if it is 2-stage or 3-stage.

It is possible for low voltage to cause the furnace to run eratically. If the conveter isn't putting out and your batteries are not charged then it could be part of your problem.
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Old 04-23-2010, 06:35 AM   #4
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The 8900 is three stage

http://www.wfcoelectronics.com/index...d=44&Itemid=77
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Old 04-23-2010, 07:48 AM   #5
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All good info. I have not yet tested the furnace shore power versus battery power. However, I can say that it failed while on shore power, and works every time (so far) on battery. I always camp on shore power. I store my TT at a storage facility and remove the battery when it is sitting. I put the battery on normal charge for deep cycle battery the day before a trip, otherwise it is not being charged or discharged when removed.

I will check the voltage at the battery and read up on the whole thing using the link provided.

Many thanks.
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Old 04-23-2010, 10:00 AM   #6
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Like Steve mentioned, if the batteries are connected and fully charged, you should have enough power for a while from the batteries alone to run the furnace. They are still in the circuit, even if the converter isn't doing it's job putting out the correct voltage. Maybe there is a short in the converter causing a voltage sag when plugged in and the batteries are feeding the converter instead of the other way around.

I would check your voltage at the battery and converter both when connected to shorepower and not. Then disconnect the converter output and measure the voltage there when plugged in. Also make sure the polarity is correct on the wiring but that should've blown a fuse.
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Old 04-23-2010, 12:30 PM   #7
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Jeeper,

I just re-read your reply and I caught something that I didn't the first time. If I had the gas to the rig turned off, and the thermostat set to "heat", the furnace would try to start but due to no gas would fail. It would try it three times then lock out. Do I have that right? Then the "remove power" step would occur when I remove the battery when I return the rig to storage (no shore power). If I have that right, it would explain why it worked when I took it to the shop and the power and gas were both available.

I am hoping I have this captured correctly and I really don't have an issue. Then it only cost me about $50 for gas and another $50 for 1/2 of shop time.
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Old 04-23-2010, 12:39 PM   #8
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Originally Posted by grandpaofthree View Post
Jeeper,

I just re-read your reply and I caught something that I didn't the first time. If I had the gas to the rig turned off, and the thermostat set to "heat", the furnace would try to start but due to no gas would fail. It would try it three times then lock out. Do I have that right? Then the "remove power" step would occur when I remove the battery when I return the rig to storage (no shore power). If I have that right, it would explain why it worked when I took it to the shop and the power and gas were both available.

I am hoping I have this captured correctly and I really don't have an issue. Then it only cost me about $50 for gas and another $50 for 1/2 of shop time.
Yes this is very possible. Luckily they have started doing the 3-start sequence on all furnaces now but not so long ago they would just run and run until the batteries were dead.

I have almost pulled my hair out in the past trying to troubleshoot furnace problems. There are so many fail safes on them that it can be very hard to pin down exactly what it is.
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Old 04-23-2010, 01:08 PM   #9
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I am going to run this by the service tech at the shop and the tech guy at Suburban. The first thing that I told both of them was I had this happen twice, and both times it was immediately after I switched out propane tanks and the gas was off.

I will also check the converter to make sure it is working properly, but I think my furnace problem may be resolved.

Thanks for all of the help.
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Old 05-07-2010, 10:09 AM   #10
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I set up camp last evening, the first time since the last post on this thread. The converter, leads from the converter to the battery, and the fully charged battery all test out at a steady 13.5 volts. I am not a skilled mechanic, but from what I have read that seems to be in the correct range.

Seems like my converter is working properly. Thanks for the help.
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