JanAndBill
Well-known member
That is correct I have 12 volt at the terminal next to the blower terminal. When I cycle the thermostat I get 12 volts on the blue thermostat wire but the blower terminal stays dead
Baby its cold outside - and inside
- Thread starter JanAndBill
- Start date
JanAndBill
Well-known member
That or pull the unit and put it on the bench. One thing I didn't mention is that the new board is different (manufacturer replaced the old number)
travelin2
Pennsylvania Chapter Leaders-retired
My replacement board has a "built in" in-line fuse...does your new board? Didn't blow that one by chance?
Also furnace has a small rocker switch the board plugs into...do you have a good connection there?
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JanAndBill
Well-known member
Dan - finally isolated the problem to a wiring problem somewhere on the furnace itself. Need to pull it so I can find the issue. I know this model pulls out the side after you disconnect the gas line, electrical and about 4 screws in the front. I'm not familiar with what's behind it though, and I can't find any detail online. Do you have to go in through the basement and disconnect the duct work, or is the duct work all connected to the outer cabinet?
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danemayer
Well-known member
It's a pretty tough squeeze to get to the duct connections. There's probably one duct connected on the front of the furnace. You might be able to pull the furnace a little, carefully, without disconnecting it - but to get it out more than a few inches you may have to take that one off. The ducts connected to the back of the furnace will probably pull out more without any stress.
JanAndBill
Well-known member
Found out the ducts are not a problem, turn the flange a 1/4 turn and they pop out. Getting the furnace out was a little more difficult, because of the way Heartland mounted the feet to the bottom of the furnace. That problem will be corrected when I reinstall the furnace.
In any case the good news, the furnace is out, bad news is with the furnace out and hooked up on the bench, it works perfectly. Soooo, now it's back to trace all the wiring out. At least now I have lots of room to work.
GETnBYE
Well-known member
Sure hope you find the problem without to much more trouble. The heat never goes out in the summer and the air never tears up in the winter!
JanAndBill
Well-known member
Finally, I think we've solved the problem. Not getting power from the coach to the furnace. Ran a another line straight to battery positive terminal, furnace worked fine. Turns out that Heartland mislabeled the fuses, or the installer swapped the wiring on the power awning and the furnace. Both use a 20 amp fuse. Once I pulled the fuse panel and traced the wire, I was able to determine the correct fuse. Pulled the fuse and in the light you could see a small burn spot in the fuse. Replaced the fuse, regained 13 volts at the furnace, and everything kicked on. Tomorrow I'll slid everything back in place and hopefully be done with this problem.
For those who need to pull the furnace. Here's some pointers on the SF42Q
1 .After you remove the metal cover from the outside, you have to remove the plastic trim around the hole to have sufficient clearance for the furnace case. Be careful, it's stuck tight with caulk. Work your way around it with a putty knife, it will break if you get in a hurry.
2. The duct work is connected to metal flanges, to disconnect from the furnace, turn the flange a 1/4 turn to line up tab with the cut out in the case and the flange pops out with the duct still connected. Neat and quick.
3. There were 4 screws driven through the case from the inside into the wall at the front of the furnace. that's all that hold's it in place.
4. Heartland "Engineering" came up with these snazzy little formed angle feet to support the furnace off the floor. Only problem is they turned the flanges out and attached them to the bottom of the furnace with screws. The furnace won't come out with them attached. To remove them you have to slide the furnace in and tilt it over so you can remove the screws. Not an easy task. Going back in I've reversed them pointing the flanges in so that you can slide the furnace in and out.
For those who need to pull the furnace. Here's some pointers on the SF42Q
1 .After you remove the metal cover from the outside, you have to remove the plastic trim around the hole to have sufficient clearance for the furnace case. Be careful, it's stuck tight with caulk. Work your way around it with a putty knife, it will break if you get in a hurry.
2. The duct work is connected to metal flanges, to disconnect from the furnace, turn the flange a 1/4 turn to line up tab with the cut out in the case and the flange pops out with the duct still connected. Neat and quick.
3. There were 4 screws driven through the case from the inside into the wall at the front of the furnace. that's all that hold's it in place.
4. Heartland "Engineering" came up with these snazzy little formed angle feet to support the furnace off the floor. Only problem is they turned the flanges out and attached them to the bottom of the furnace with screws. The furnace won't come out with them attached. To remove them you have to slide the furnace in and tilt it over so you can remove the screws. Not an easy task. Going back in I've reversed them pointing the flanges in so that you can slide the furnace in and out.
JanAndBill
Well-known member
The only other time I can remember something similar was on a 12 volt light circuit that had an open ground. Since the wires were all disconnected at the furnace end, I don't know if this had anything to do with it or not.
Rain and other problems delayed me in finishing up, but the furnace is back in place and working fine. Once that was back I was able to repair the dripping water line (that started leaking when i bumped it taking the furnace out). Finally everything buttoned up and back in operation.
danemayer
Well-known member
The LEDs on the fusebox that light up to let you know when a fuse is blown also allow a small amount of current to flow down the circuit. I've noticed that if the fuse for the TV signal booster is blown, the red light on the signal booster may still get enough power to light up. I've also seen LED overhead lights getting enough power to be dimly illuminated despite a blown fuse.
jimtoo
Moderator
Also to blow your mind a little... if you take a digital volt meter and check across a fuse to see if it is blown...and the LED is on ,,, your meter will read 12.5v on LED side of fuse and 13.5v on power supply side. (Normal 12v circuit voltage) So if your checking with volt meter it can make you think fuse is OK if your in a hurry and not looking at reading close... cause how can voltage go through a blown fuse??? It is voltage feeding backwards to the LED to make it turn on. ,, It almost drove me nuts a while back when I was checking for a blown fuse with meter. Of course most folks will say I am close anyway.
Jim M
Jim M
JanAndBill
Well-known member
I wondered if that was causing the voltage reading. I also don't understand why the red led was NOT lit on the blown fuse. In fact none of the led's would come on if I pulled a fuse out.
danemayer
Well-known member
The LED only illuminates if the circuit is turned on, providing a path to ground.
travelin2
Pennsylvania Chapter Leaders-retired
Here's a pic of one of my "blown" fuses. Enough voltage was passing thru to dimly light the led's in the kitchen slide even after I repaired wiring that had been compromised.
See how the filament is twisted back and welded itself to complete a circuit.
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See how the filament is twisted back and welded itself to complete a circuit.
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