Furnace not firing on 12V

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Furnace not firing on 12V

September 24, 2011, 05:21:34 pm

We did our first dry camp last night. Temp dropped to 40 out. Turned the furnace on and no heat. The fan comes on but the flame doesn't. I turned on the generator and I got flame. Any ideas?

I'm in Mesa Verde NP so no net access. I'm standing on a mountain to get this out! I'm pretty sure I'll be slow to respond.

See ya
Ken

Re: Furnace not firing on 12V

Reply #1 – September 24, 2011, 05:32:49 pm

Since the furnace worked with the generator running (i.e. 12 VDC house battery receiving a charge) but not on battery alone, the most likely issue is LOW BATTERY VOLTAGE.

The furnaces start sequence is:

Thermostat on
Fan starts
Fan moves enough air to close the SAIL SWITCH.
The sail switch circuit tells the PC board that there is enough CFM of air to open the GAS VALVE and trigger the IGNITOR.

Causes of open sail switch, so nothing but fan runs:
1. Low voltage-- fan turns too slowly
2. Restriction in air return
3. Restriction on outlet side such as crushed hose or too many closed vents.

Start by checking voltage at the house battery and also at furnace when this occurs. 12.7= fully charged battery. 12.2= 50% discharged battery.

Brett

Re: Furnace not firing on 12V

Reply #2 – September 24, 2011, 06:29:50 pm

Ken, if you need internet service go to Mesa Verde RV resort. Less than a mile down the road. The security code for WiFi is 9705337421. Sorry we missed you this A.M. We are now in Gallup. Just a might tacky...

Re: Furnace not firing on 12V

Reply #3 – September 25, 2011, 02:43:25 pm

Brett,

You where right about the batteries being low. We moved to a spot with hookups the next morning and after a couple of hours I switched off the breaker, turned on the furnace and it fired up with no trouble on the batteries.

So I pull the battery cover to check the batteries and now I think I have other issues...

When I opened the battery box one of the cells is leaking. You can barely see the on right most battery the right rear cell has fluid around it. That can't be good.

I assume that's from the cell boiling? I just installed a Progressive Dynamics Inteli-Power 9280 about 6 weeks ago. It's not supposed to do that! The batteries are fairly new installed in May this year at FOT. Deka 8D wetcells. Does that mean I have a bad cell in that battery?

Also I'm starting to think the batteries are not wired correctly. It looks like the right battery is wired solo so I figured this was the starting battery. When I pulled the negative cable on it all of the house 12v died but all of the dash lights where working. It looks like maybe the batteries are hooked up backwards? That is the 2 house batteries are hooked to the starter and the starter battery is hooked to the house?? I making the assumption that I should have 2 house batteries and 1 starting battery. That's the norm right? The 2 batteries on the left/middle have a jumper from positive to positive that ties them together in parallel which leads me to believe they are the house batteries. (in the pic the left terminal on each battery is negative)

Can anyone tell if the battery cables are attached correctly from the picture? I can post a higher res one if necessary.

see ya
ken

Re: Furnace not firing on 12V

Reply #4 – September 25, 2011, 03:24:29 pm

Since these are wet cell batteries, use a HYDROMETER (from any auto parts store-- under $10) to check the SG (Specific Gravity) of each cell. That will tell you very quickly if you have bad cell. The hydrometer is used on fully charged batteries.

Brett

Re: Furnace not firing on 12V

Reply #5 – September 25, 2011, 04:17:37 pm

Ken, my battery setup is entirely different than yours. I always thought you had a Detroit 6V92 350hp. Is that correct? If so, my coach has three red top starting batteries and 2, 8D Gel Cells for the house batteries. My starting batteries are located back in the engine compartment and the house batteries are behind the drivers real wheel.

Re: Furnace not firing on 12V

Reply #6 – September 25, 2011, 04:34:57 pm

Brett,
We have found over the years of playing battery games, the specific gravity test alone is near worthless, Can load test, but all this takes time. The big reason we have gone to the Sigtronics Electronic Battery Tester system, it is a digital sniffer, preset the CCA of the battery, and have never had it screw up. Surely do not know how it works, but is sure is accurate, the reason we use it, to determine if the lead acid battery in generators are capable of making it until next PM. Have reduced or eliminated our battery failure calls by a big number.
No one wants to buy batteries, Our policy is; Tester shows it needs replaced, and the customer says no, the 0300 phone call for bad battery gets very costly

Not to mention stupid, but we all know you can not fix stupid, Just charge for it.

Re: Furnace not firing on 12V

Reply #7 – September 25, 2011, 04:39:29 pm

Make sure your battery isolator is working and charging both batteries while engine is running. Leaking cell on the battery could be caused by it being low, shore power brings it back up but heats the battery a bit and the electrolyte expands and a little bit comes out the cap. So, your battery may be OK and just a symptom of another problem.

Can't really see which battery is leaking in the photo. When the batteries were replaced, it would not be the first time cables were put on wrong batteries. One of the members had a good point about taking a foto before taking off the cables to change. I use a labeler to make sticky labels to wrap around each cable. If you disconnect the engine battery, the ignition solenoid under the dash should go dead. If you disconnect the house battery, most of the fuses under the dash should go dead. Mine was wired incorrectly when the isolator was changed. You have a different model so fuses may be at a different location.

A fast charging battery produces a lot of hydrogen gas. Avoid removing battery cables until battery box has aired out a bit.

Another reason I like my two dash mounted digital voltmeters. I can see exactly what the voltages are at any time and see most problems coming a long way off (hopefully).

Re: Furnace not firing on 12V

Reply #8 – September 25, 2011, 05:10:29 pm

It would appear that they put the jumpers on the wrong set of batteries, based on your comments. The left battery is probably for the chassis and the right two batteries are for the house.
Regards,

Re: Furnace not firing on 12V

Reply #9 – September 25, 2011, 05:16:49 pm

At least on our 1993, the cables have labeles affixed by Foretravel. Pull out your wiring diagram and match the numbers to their correct location on the batteries (house vs chassis).

Too many years with likely too many different batteries installed by different people to KNOW what was OE. Make sure that you have enough CCA for your engine-- that may (or may not) require two 8D batteries as start batteries.

Re: Furnace not firing on 12V

Reply #10 – September 25, 2011, 06:21:58 pm

Brett,

Our 1993 U300 does have white labels on the cables but time has taken it's toll on the black printing. Under dash is fine but printing on battery compartment, isolator panel or engine compartment cables is long gone.

Yes, the Detroit does take three 34 or 27 series or two 8Ds. 19 to 1 compression ratio compared to 14/1 on a Cat makes it mandatory.

The wiring diagram is a life saver. Good to go to a print shop and have it made into blueprint size and then stored in a mailing tube in a cabinet. The stock size is almost impossible to read in low light or with ancient eyes.

Re: Furnace not firing on 12V

Reply #11 – September 25, 2011, 06:53:53 pm

Quote from: kenhat – September 25, 2011, 02:43:25 pm

Brett,

You where right about the batteries being low. We moved to a spot with hookups the next morning and after a couple of hours I switched off the breaker, turned on the furnace and it fired up with no trouble on the batteries.

So I pull the battery cover to check the batteries and now I think I have other issues... When I opened the battery box one of the cells is leaking. You can barely see the on right most battery the right rear cell has fluid around it. That can't be good. I assume that's from the cell boiling? I just installed a Progressive Dynamics Inteli-Power 9280 about 6 weeks ago. It's not supposed to do that! The batteries are fairly new installed in May this year at FOT. Deka 8D wetcells. Does that mean I have a bad cell in that battery?

Also I'm starting to think the batteries are not wired correctly. It looks like the right battery is wired solo so I figured this was the starting battery. When I pulled the negative cable on it all of the house 12v died but all of the dash lights where working. It looks like maybe the batteries are hooked up backwards? That is the 2 house batteries are hooked to the starter and the starter battery is hooked to the house?? I making the assumption that I should have 2 house batteries and 1 starting battery. That's the norm right? The 2 batteries on the left/middle have a jumper from positive to positive that ties them together in parallel which leads me to believe they are the house batteries. (in the pic the left terminal on each battery is negative)

Can anyone tell if the battery cables are attached correctly from the picture? I can post a higher res one if necessary.

see ya
ken

Ken, I just checked some photos I had taken of my old 93, U225 battery compartment. It looks just like yours. I determined that the there are Three positive cables, red end, and two negative cables, black end, coming through the back of the compartment. Where they are grouped with two positive, red, cables and a black coming out together they go to the starting batteries. Where you see just two cables close to one another, these cables go to the house. Considering the need for starting power for the 6V92, this makes sense.

I hope this helps.

Re: Furnace not firing on 12V

Reply #12 – September 25, 2011, 06:57:34 pm

Pierce, Thought you would like a little info, on emergency generators, normal battery setup is a pair of Grp 31 batteries for a 6V-92. for 24 VDC setup.
Speaking of the 92 Series, I can not find the info in print anymore, but I seem to recall the turbo 92 at 17 / 1 comp ratio, and the N/A 18.7 / 1 Comp ratio.
Also found only the US Govt can get the 2 cycle DDC engines anymore, everyone else, nope. Since they have been outlawed and Damler took over DDC, all bets are off.
Cheers

Re: Furnace not firing on 12V

Reply #13 – September 25, 2011, 07:53:49 pm

Dave,

Never had a 24V setup like GM 4907 bus. As I remember all GM busses had two 8Ds also. Other busses too. While a Detroit (or most other diesels) will start in good weather with a single 8D, cold weather starts with a longer cranking time require two 8Ds or as Foretravel has done, three smaller batteries (for the U300). High altitude and cold weather can really make diesels difficult to start and require clean terminals and connections besides the right batteries (plus block heaters).

Emergency generators usually have VERY short cable runs to the starter motor so minimize the voltage drop.

If too small of a battery (CCA) is installed, extended or even normal cranking can cause cell connectors to fail. Naturally, it then becomes a zero volt battery. Also why you have to match engine to battery cranking amps.

Will have to find the source for compression ratio and forward when I get ahold of it. Not saying you are wrong at all but want to check where I got it.

While you may not be able to purchase a new, out of the box 6V-92TA, there are still lots of shops that rebuild them and tons of inexpensive parts available. The 6V-92TA has removable liners so may be rebuilt forever unless a main bearing has spun or the like. New heads/blocks are also available. Ebay also has a lot of parts including very inexpensive turbochargers.

Not all Foretravel diesels have liners so with major bore wear or any kind of cylinder wall damage, they may not be a candidate for rebuilding.

Re: Furnace not firing on 12V

Reply #14 – September 25, 2011, 08:39:32 pm

Pierce,
As for all I know, all buses were 24 VDC. on the MCI 7, it has a 250 amp alternator that had to pass a load test of 250 amp output at 27.9-28.0 Volt , weighted about 250 lbs, has 4 Vbelts on it with the air cylinder belt tightener .
I removed 99% of the origional electric stuff, and used a 70 amp 24 V Leese Neville alternator, more thanenough, to run lights and dash lights, that was the only 24 V items left. Heck the condenser fan was a 5 hp and the fan for air handling was 3 hp, so you get thepixutre why all the big amps needed, It all went out in the junk pile.

For sure, check out the comp ratios, I might have most a marble or two.
I am getting ready to escape out of here for a while 1 week or maybe a month of so, time will tell.
Cheers, and get a resonator on that 92.
Cheers

Re: Furnace not firing on 12V

Reply #15 – September 25, 2011, 09:42:46 pm

Thanks for all the comments guys. Although I think I'm even more confused now!

Gathered a few more facts for you.

Batteries are all Deka 708D CCA 1340@32° 1100@0°

Using the Rapid Test Battery Tester (cheap plastic hydrometer from AutoZone) on the house battery. The right most battery in the previous photo.
1.3+v 1.3-v
1.3+v 1.3-v
1.3+v 1.3+v
Top numbers are the rear most cells. The battery has been on the converter/charger approximately 7 hours and was running during tests. The tester only showed Good, Fair & Needs Recharging on the scale. 1.3 was the high end of the "Good" section.

Attached is the only wiring diagram I could find that showed the batteries. It shows 2 coach batteries and 1 starting battery but doesn't spec CCA or anything except - and +. Plus the drawing was done in 3/14/90 so not sure if this is just a generic wiring diagram of the time.

Pierce, Dave the flyers in my manual shows the 6V-92TA DDEC Parlor Coach 300-350HP at 17 to 1 compression. I like that name "Parlor Coach".

I'm open to any suggestions but now until I get home in November I'll keep a pretty close eye on the batteries, avoid dry camping and take it in to my favorite shop in Denver (Stewart & Stevenson) when home and have them take a look.

I asked this in another thread but didn't get a reply so I'll try again here.

Since the Progressive Dynamics Inteli-Power 9280 has the charge wizard that throttles back the voltage as the batteries charge would there be any problem leaving the boost on when I'm hooked to shore power? It's supposed to drop down to 13.2V when in storage mode.

see ya
ken

Sorry the photo is sideways. I had to use my iPhone to capture it and not sure how to rotate it.

Re: Furnace not firing on 12V

Reply #16 – September 25, 2011, 10:05:27 pm

Ken,
My '92 U-280 has the identical fiberglass case and three 8 D batteries; however, your cable setup is just the opposite of mine: The far left battery (on mine) supplies the starter and is the engine battery and the cables extend to the left just as you two left cables do. The center and right batteries (on mine) are connected in parallel (+to+, -to-). My engine battery has 3 cables leaving it, whereas house batteries have two exiting the case. I am attaching a pic of the arrangement in my coach. Understand, my LEFT battery is the starting battery.

Without seeing where the large cables go, it's impossible to be certain as to their destination, but your cabling is the reverse of mine.

Re: Furnace not firing on 12V

Reply #17 – September 25, 2011, 10:35:54 pm

Don you are my hero! You get karma points from me.

Looking at your battery setup I'm pretty sure mine are wired backwards.

When I bought the coach the battery box lid was missing. When driving my coach back to Denver from Corbin, KY (where purchased) I had a rather nasty meet up with a black pole in a black asphalt parking lot at night that putty knifed the drivers rear quarter of my coach. A very long whole other story that I won't go into now. The result was that I ended up taking the coach to FOT for repairs instead of Denver.

FOT replaced the battery box as part of the repairs. The batteries where shot so I had FOT replace them at the same time. I'm pretty sure this when the hookups where reversed.

Now I need to figure out what cable goes where and get dangerous!

see ya
ken

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Furnace not firing on 12V

September 24, 2011, 05:21:34 pm

Re: Furnace not firing on 12V

Reply #1 – September 24, 2011, 05:32:49 pm

Re: Furnace not firing on 12V

Reply #2 – September 24, 2011, 06:29:50 pm

Re: Furnace not firing on 12V

Reply #3 – September 25, 2011, 02:43:25 pm

Re: Furnace not firing on 12V

Reply #4 – September 25, 2011, 03:24:29 pm

Re: Furnace not firing on 12V

Reply #5 – September 25, 2011, 04:17:37 pm

Re: Furnace not firing on 12V

Reply #6 – September 25, 2011, 04:34:57 pm

Re: Furnace not firing on 12V

Reply #7 – September 25, 2011, 04:39:29 pm

Re: Furnace not firing on 12V

Reply #8 – September 25, 2011, 05:10:29 pm

Re: Furnace not firing on 12V

Reply #9 – September 25, 2011, 05:16:49 pm

Re: Furnace not firing on 12V

Reply #10 – September 25, 2011, 06:21:58 pm

Re: Furnace not firing on 12V

Reply #11 – September 25, 2011, 06:53:53 pm

Re: Furnace not firing on 12V

Reply #12 – September 25, 2011, 06:57:34 pm

Re: Furnace not firing on 12V

Reply #13 – September 25, 2011, 07:53:49 pm

Re: Furnace not firing on 12V

Reply #14 – September 25, 2011, 08:39:32 pm

Re: Furnace not firing on 12V

Reply #15 – September 25, 2011, 09:42:46 pm

Re: Furnace not firing on 12V

Reply #16 – September 25, 2011, 10:05:27 pm

Re: Furnace not firing on 12V

Reply #17 – September 25, 2011, 10:35:54 pm

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