Munchkin 140M Air Switch

OldSkool

Homeowner with a Munchkin 140M installed in 2004.  This Munchkin has the Honeywell gas valve (it's called a Munchkin Gas Valve in the IOM Manual but it's Honeywell on the underside sticker) and a 925 controller; this 140M was manufactured 11/03 (s/n #K18J2227).  The original 925 control board failed in March of 2005.   Working with the wholesaler in Denver, I replaced the low voltage harness on 3/17/2005 and then the control board on 3/18/2005.  The unit has been functioning as advertised  since.

 

At the time that I swapped out new 925 control board for the original one, I made note of the fact that there was no Air Switch on the new 925  (P-04 version) control board.  It's been 7 years or so now, and to be honest I do not remember what steps I took relative to the Air Switch being deleted on the new board.  In the process of getting ready to clean the unit recently I noticed the pair of unhooked pink wires marked as BVP that I had zip tied together inside the unit back when I did the controller swap.  Since I had changed the low voltage harness as well at the time that I changed the control board I believe the designation on the harness for the air switch changed to indicate the Blocked Vent Pressure sensor (that this 140M does not have because of its age (built in 2003)), and that is now supported by the newer 140M 925 control boards.

 

In December of 2011, member IceSailor on the Heating Help forum here posted as part of a thread that he was helping out on, that he had smelled gas inside a Munchkin, and upon investigation (I'm paraphrasing here), had found that a rodent had chewed away the cap on the hose that was left over when the Air Switch on the unit he was working on had been removed.  That's the thing, I don't remember capping a hose when I did mine, and when I look all over inside this 2003 Munchkin I do not see any hoses anywhere.  I know that I had an Air Switch on the original control board.  Any ideas on where the hose for the now not present Air Switch ties in at the end opposite the control board?

Every so often, if I get right down and put my nose right by the joint between the case and the removable top/front, I can detect what remotely smells to me like gas (my wife can't smell it).  I have checked for leaks using leak checking liquid (not soap), and there are no gas leaks in the gas line, interior shut off valve, or the aluminum 1/2" NPT connector on the Honeywell gas valve... none.  So I'm wondering if I missed something way back when I did the board swap.  I know that the later models of the 140M have latches on the case cover, along with a gasket between the case and the removable top/front, and a longer postpurge fan run on the latest 925 (and 926) control boards, perhaps showing a recognition by HTP that a small amount of unburnt fuel/air mixture can still be present after the shorter postpurge fan-run in the older models.  I just don't know on that, but I would like to make sure I did the board swap completely.

 

Thoughts on any of this would be greatly appreciated.   Thanks.

Jr_12

OldSkool

The pressure switch hose connects to a nipple at the base of the Blower motor. By base I mean where it would connect to the spacer block on the right side(if you're facing it). If you have replaced the blower it might not have the nipple.

OldSkool

THANKS JR.

I had not looked there.  I'll take the cover back off and check around/under the blower motor, as you indicate, tonite.  Thanks again.

OldSkool

Photo of Air Switch hose boss

Here is a look at the location where the Air Switch would be attached to the blower motor.  As it turns out, this particular unit never had an Air Switch as it can be seen that the hose boss is not drilled out.  Thanks JR for helping me make sure I didn't have a leak source.

Jr_12

No Problem

Did you have a gas smell? Everything from the blower down to the combustion chamber is at a positive so you would only smell it while it's running. Glad I could help though!

OldSkool

Very minor smell

The smell, which is very slight, is just after the boiler has completed a call for heat.  I was just hoping this might have explained it., but the positive pressure, as you have noted, would result in a different timing of the smell.   The random smell seems to be dependent on the breezes outside, and the boiler just completing a call for heat (at least that's my impression).  It is not every time or even every 10 times, just randomly, every so often.

 

I've made a final improvement at the concentric vent termination just in the last few days, and that may have finally solved the random slight smell.  As background, I live on a ridge near the base of Pikes Peak, and several times a year I will have the Munchkin halt with an F10 error; the wind at a certain angles and velocitys is/ was actually blowing out the burn via the side-house mounted concentric termination.   This area gets what are known around here as Chinook winds, and they are really something.  It could very well be that several things are going wrong at the house sidewall at the the Concentric Vent Termination, including blowing out the flame, and in lighter breezes moving exhaust flue gasses back into the intake.  (Certainly the slight rust on the incoming gas line inside the Munchkin here may indicate this.)  I think I may start a new thread and try to see what steps may have been taken by someone else to cut down on the impact of wind and breezes, and to share what little I can on the subject.  Thanks again for your help JR in eliminating one important and possible culprit.