Replaced the furnace control board

[danemayer]

Our furnace quit a few days ago. The initial symptom was that the blower would run for about 20 seconds and then shut off. Recycling the thermostat caused it to try again with the same results.

I investigated earlier, during blizzard conditions. Didn't go well - my bad. So today I took another run at it with help from a local service guy. We re-checked and verified all the wiring connections, and then located the sail switch and verified it's operation and that it and the high-limit switch were providing power to the control board. But alas, no power getting out of the board.

In preparation for this trip into extreme cold weather, a few weeks ago I ordered a control board to have on hand. In shopping, I found that Suburban had come out with a new board 521099 that is common to the furnace and water heater, and a little less expensive than the older board, 520820.

Installed the new board today and all is well.

 

[JohnDar]

Some time back, I was having trouble with the water heater on propane, so I bought another circuit board for it. Didn't cure the problem, but I kept the old one anyways. So, it looks like I now have a spare that might work in the furnace, as well. Nice.

 

[MCTalley]

Because I recently paid a mobile tech a total of $400 to replace the board on my furnace, I have to ask how difficult or easy it is to remove and replace the board? I had taken a quick look at it initially before just calling the mobile tech to repair it for me (money well spent since the overnight temp was going to be below freezing that evening).

 

[danemayer]

Because I recently paid a mobile tech a total of $400 to replace the board on my furnace, I have to ask how difficult or easy it is to remove and replace the board? I had taken a quick look at it initially before just calling the mobile tech to repair it for me (money well spent since the overnight temp was going to be below freezing that evening).

Once the cover is off, there are 2 easily accessible screws holding the bracket to which the board is mounted, and a couple of lock nuts holding the board to the bracket. The board and it's mounting bracket have to be carefully wiggled out. Pull the fuse (in the fuse panel) first. It's a relatively easy replacement IF nothing goes wrong, like wires coming off other components, or mounting clips breaking, or wires inside wire nuts coming loose. But if stuff goes wrong, it gets way harder. That's where the experience of a tech pays off.

 

[rpotter]

I had this exact same problem in an outback 260fl travel trailer. It finally turned out to be a tiny bit of dog dander that got sucked up in thru the intake slits in the trailer and had landed on the circuit board. The service tech vacuumed the circuit board and problem was solved.

 

[wdk450]

If dog dander getting across modern circuit board FET circuit paths causes problems, these boards should be sealed with coating sprays/dips by the manufacturer. This protects these circuit boards from debris, but makes component level troubleshooting and repair about impossible. This is O.K. because everyone replaces the entire board anyways.

I believe the Dinosaur Electronics boards are so protected. They have built circuit boards for NASA.

 

[rpotter]

This could be quite true. It was a mobile repair guy. He took out the circuit board, vacuumed it, put it back and the problem never returned. That was his explanation but it may have been that when he put in back a loose connection was inadvertently fixed.

 

[pegmikef]

Back in the 70s I had a tech fix one of my Data General mini computers by vacuuming the main frame cabinet slots and cards. I had them installed in mobile commo huts and according to the tech, the constant movement and bouncing had apparently caused a tiny piece of solder to fall in just the wrong place and caused a short. Of course quality nowadays is markedly different.