10 replies to this topic

[jb8103]

Model # might be MMHB.

Short cycling problem has been going on for a year but getting worse. No airflow problem. Main hi limit rated 140, seems fine, auxiliary limit shuts down everything nicely when disconnected.

T-stat Lux 500. Heat anticipator problem?

[Dan Webster]

[jb8103]

I doubt it's the flame sensor since it stays on for a minute or two, but it's worth checking the basics when I go back there. Didn't have much time last night.

[Dan Webster]

Let us know what ye find out.

[jb8103]

Can't find any literature on this model #. Also have a problem opening PDFs on NordyneU, not that they have the model listed anyway. There's no circuit board in the old beastie, therefore no codes, therefore I'm on my own.

Customer highly suspects the t-stat is goofy, can't say I disagree.

First thing I'll do is prove out the t-stat. Customer wants it replaced with a Honeywell T1 type anyway. If it's not that, then the gas gun and igniter come out for a look-see and cleaning. If it's not that then the limits come out one at a time, even though limits don't have this kind of fail mode, ya never know.

[RegUS_PatOff]

... Model # might be MMHB
.... There's no circuit board in the old beastie, therefore no codes,

1) yes, I believe
2) ... are you sure ?
... three blinks ... Ignitor Failure
That model uses the Igniter as a Flame Sensor ...
Was the Igniter ever replaced with a universal (flat) one ?
The original igniter is a small round coil 902661

wiring diagram
MMHB-070.pdf

click on picture

[jb8103]

Yep, that's very close, Reg, in fact looks like a revision of the diagram on the door, rendered on a 4x5 sticker, which I've been trying to decipher with the aid of a magnifying glass the last two evenings. I'd like to know how you found an MMBH wiring diagram when I could not, that might be the best learning experience for this episode. Second best would be if you could show me where the error code LEDs are on this diagram.

Note the fan switch, which is make on rise and adjustable from 90 thru 120, rather like an old fan limit switch. There is a little dial that can be turned with a screwdriver. I set it to 110. I pulled the old Lux 500t-stat off the wall and jumped R to W. I expected the blower to keep working but it did not. Still had flame.

I don't know the config for the igniter but from the drawing it should be a typical "glowbar", not a coil. Ohms out at 140, so there is definitely a problem there.

Edited by jb8103, 18 October 2011 - 10:00 PM.

[RegUS_PatOff]

... I'd like to know how you found an MMBH wiring diagram when I could not,
... Second best would be if you could show me where the error code LEDs are on this diagram.
... fan switch, which is make on rise and adjustable from 90 thru 120,
... a typical "glowbar", not a coil. Ohms out at 140

1) I could tell you, but then you'd have to kill me... . . . wait... that's not right...
p.s. it's MMHB (after a few hours of searching for MMBH)
just happened to find it.. you know, like when your searching for porn and all this other furnace info pops up
.. .. wait.. ahh.. I mean the other way..

2) Intertherm Ignition Control Module 626421 fits models MM(H,B)A and MM(H-B)B
RED Flash codes
1 Flash - the control is in lock-out because the inducer pressure switch is or was stuck closed
2 Flashes - the control is in lockout because the signal was not received by the control that the inducer pressure switch had closed within the time
3 Flashes - the control is in lockout because a failed ignition attempt, a gas valve error or a false flame sensed during the warm up period.
If false flame has been sensed, the control will return to normal operation, and repeat ignition sequence when the false flame is not present
4 Flashes - the control is in lockout due to a failure within the control board

3) bad Fan Switch ? . . . Does the Fan work when the Wall Thermostat is set for "FAN" ? . . . (or jumper G to W)

4) It IS a "typical" glowbar, but needs to be the round Carborundum type (140 OHMs is OK)
Flat Ignitors are Norton type
They have different characteristics and both types are used in household appliances.

[Dan Webster]

Dayum it boy I is gonna have ta start takin notes, they don't call you the Grand Master Funkaliciousness fer nuttin.

Edited by applianceman18007260692, 18 October 2011 - 11:27 PM.

[jb8103]

It is MMHB, I keep transposing those letters for some reason. Bad juju when searching model numbers. Even so I can't find what you found.

Instead of an Intertherm, this has a United Technologies Series 1018 Ignition Control, no codes. Just a black box. That's the other thing, too, there is no pressure switch on this gem of a furnace, when there really should be. If I'm not mistaken all the old Millers were forced draft, meaning positive pressure in the heat exchanger, which is awful.

For the igniter I'll have to have that gas gun out of there and take a look, I used my allotted time last night pulling more t-stat wire, his was chewed up.

I admit I am putting a little sales pressure on this customer, he really needs a better furnace. Besides this one is 16 years old and I bet we find a cracked heat exchanger anyway, which is what we're going to look for on my next visit before I order any parts. He's already got the new t-stat, that's a good start.

And the A-man is right, Reg, you is pretty dayum good.

Edited by jb8103, 19 October 2011 - 05:13 AM.

[jb8103]

Got it. Spiders in the orifice, loose connections in electrical box. Couldn't even sell an ignitor on this call.

Something else - Honeywell apparently makes two T87 types, for example a T87N heat/cool thermostat that I can get from my supply house, and a CT87N they market through Lowes and Home Depot.

The CT87s are junk. I've had two bad off the shelf. Get the T87.