Older Harman Accentra vacuum tube question

[SciGuy]

I'm just wrapping up the rehab of an older Harman Accentra that I purchased with the intention of resale. The original owners has been rather lax on maintenance. At some point they removed the vacuum switch and jumped it. I've replaced the burn pot, flame guide, door glass and gaskets, hopper lid gasket, air grill, ESP and combustion blower. Today I fired it up to check the it for appropriate function. My Dwyer gauge indicated a vacuum or .40"wc and ignition occurred in just over 10 minutes. The flame increase for a few minutes but when I set the control to 5 in stove temperature mode the stove reached a point where the feed light would illuminate but the auger wasn't turning. I switched to room temperature mode with the same results. I began to worry that the computer had $hit the bed but decided that the most obvious thing that could cause the auger to not run when the feed light was on was the vacuum switch. Despite still showing a nice strong .40"wc of vacuum, I jumped the vacuum switch and low and behold the stove functioned perfectly. This outcome led me to imagine that the vacuum tube was partially blocked and at warmer temperature the draft it provided to the switch was just low enough to not close the switch. So I first blew on the tube with my mouth and then applied some canned air. In hindsight, the canned air might have been an over exuberant idea because when I did there was a "pop" that occurred with debris be dispersed from an unknown location. When I reconnected the vacuum switch to the system it no longer closed to allow the auger to function at all.

So perhaps I've split the tube or disconnected from where it's connected to in order to sense the vacuum.

So my question before I just tear into this willy nilly:

Where does the silicone tube connect to and is it possible to install a new one?

Thanks for any insights you might have. I'd really love to wrap this up.

Hugh

 

[tiger]

I"m curious what you find even if I can offer no useful input; but my mind went elsewhere when you said "older" and "vacuum tube", as in... exactly how long HAVE they been making Accentras?

 

[SciGuy]

I"m curious what you find even if I can offer no useful input; but my mind went elsewhere when you said "older" and "vacuum tube", as in... exactly how long HAVE they been making Accentras?

I believe they have been made since ~ 2002. The innards have evolved a bit over the years but the exteriors look pretty much the same.

 

[Washed-Up]

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[SciGuy]

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Thanks Washed-Up for the intended help. Sadly the Harman parts diagram which I have on hand doesn't seem to do me any good what so ever. Pellet parts does list 9mm silicone tube and sell it for $36 for 6ft but as I understand things the one I'm looking for is 14" and I really need to know its path and how to install it.

Still searching for that information.

 

[Washed-Up]

Are you talking about the “gummy fix” if so, this should help…https://www.hearth.com/talk/threads/harman-accentra-gummy-stove-syndrome-solution.45548/

 

[SciGuy]

Are you talking about the “gummy fix” if so, this should help…https://www.hearth.com/talk/threads/harman-accentra-gummy-stove-syndrome-solution.45548/

View attachment 285771

Not the gummy fix. Just where does the silicone tube that actuates the vacuum switch lead to when it leaves the vacuum switch. Rickwai is working with me on this via conversations at the moment.

 

[tiger]

I believe they have been made since ~ 2002. The innards have evolved a bit over the years but the exteriors look pretty much the same.

So, the vacuum tube involved did not look like:

 

[SciGuy]

So, the vacuum tube involved did not look like:

My father was a TV repair guy back in the 1950 when all TVs used such components. I can still remember him reaching into a turned on TV set in the living room with a kitchen knife and tapping several of the tubes in an attempt to improve their connection. I got the job os saying whether the picture was better or not after each tap.

I debated calling it a hose, pipe or tube thinking of just what you thought of. I believe Harman calls it a tube.

It's now looking like my problem isn't the tube itself as I'm seeing a decent measured vacuum at the tube when in "test mode high" but a very weak one when low vacuum is cycled to.

 

[Ssyko]

im not a harman guy but it should connect to the back side of the firebox or in the path ahead of the combustion blower. may take a good flashlight and a mirror, and probably a minor amount or contortion to find the nipple it goes on.

 

[SciGuy]

im not a harman guy but it should connect to the back side of the firebox or in the path ahead of the combustion blower. may take a good flashlight and a mirror, and probably a minor amount or contortion to find the nipple it goes on.

Hi Ssyko,

Rick Wai tells me that it enters the air intake pathway and snakes a ways down the corrugated tube that runs down into the firebox.
This morning I ran the stove in test mode where it alternates between high and low draft. I was seeing ~.57"WC in high draft mode and then a drop to ~ .10"WC at low draft . Draft reading taken at the end of the tube where it mates with the vacuum switch the values where ~.40"WC and .05"WC respectively. The vacuum switch requires .15"WC so it was dropping out the auger at the low level.

Harman calls for a high draft of .50-.60"WC so the stove looks good. For the low draft reading they call for .35-.45"WC which is way higher then the stove is producing. It's got me stymied at this point. I've got a new control board on hand but hate to install unless all else fails.

 

[Ocelot]

I don't have an Accentra, mine is a P43, but that's weird that it drops so low. When I tested and adjusted mine to spec with the little adjustment pot screw, mine was initially too high, like .72 or so and the low in the .50's on low, and that adjustment pot was really sensitive Just a maybe 1/6th turn on the screw would drop or raise it noticeably. Anyway, point being I had to turn it down to get .5 to .6 on high and the low followed accordingly. I wonder if you have a leak somewhere in the firebox not far from where the tube connects? That may explain the difference in draft on the tube itself vs the test port and lower everything overall.

 

[SciGuy]

I don't have an Accentra, mine is a P43, but that's weird that it drops so low. When I tested and adjusted mine to spec with the little adjustment pot screw, mine was initially too high, like .72 or so and the low in the .50's on low, and that adjustment pot was really sensitive Just a maybe 1/6th turn on the screw would drop or raise it noticeably. Anyway, point being I had to turn it down to get .5 to .6 on high and the low followed accordingly. I wonder if you have a leak somewhere in the firebox not far from where the tube connects? That may explain the difference in draft on the tube itself vs the test port and lower everything overall.

Rick W. and I have both come around to thinking that the problem is likely a control issue i.e. computer board. My next step before replacing the board is to test voltage at the combustion blower to see how much drop off is occurring in test mode when the stove cycles from high to low draft. It doesn't seem to make sense that the high draft is appropriate but the low is so low.

 

[Mt Bob]

Draft readings should be taken at the test port.

 

[SciGuy]

Draft readings should be taken at the test port.

Agreed, but if for some reason the vacuum switch isn’t seeing more tha ~ .15”wc you won’t have feed occur. With a new board installed my high draft at port is .57”wc and low draft is now .44”wc so all is right with the world

 

[Ocelot]

Agreed, but if for some reason the vacuum switch isn’t seeing more tha ~ .15”wc you won’t have feed occur. With a new board installed my high draft at port is .57”wc and low draft is now .44”wc so all is right with the world

Glad to hear it's finally all worked out!
Does yours have the little adjustment screw? If so it might not be a bad idea to check it again after the new combustion motor is broken in. Mine actually went up a little after a couple days of running. Then adjust it right to the middle of the recommended range. As long as the flame is good, I like to keep mine no higher then middle of the range to save a few BTU from going up the vent.

Ray

 

[SciGuy]

Glad to hear it's finally all worked out!
Does yours have the little adjustment screw? If so it might not be a bad idea to check it again after the new combustion motor is broken in. Mine actually went up a little after a couple days of running. Then adjust it right to the middle of the recommended range. As long as the flame is good, I like to keep mine no higher then middle of the range to save a few BTU from going up the vent.

Ray

Yes it does have the classic low draft adjusting screw. I plan to run the unit a few hours tomorrow to check for perfect function and will tweak it if needed.

Thanks for the advice.

Hugh