Nordyne E2EB 015 Sequencer not sequencing

[jgolomb]

Hi! Our troubles began when the heat wasn't coming, fan worked fine when turned to on and with the a/c - nothing with heat setting. So after some diagnosis and searching on here I narrowed it down to the sequencer (or so I thought)
Ordered a new sequencer, while waiting for it, took the whole blower out and cleaned it per instructions found on this site. My only issue there is that I'm not 100% sure if I hooked the capacitor leads back to the correct places on the cap itself although it does not appear to be a polarized cap.
Got the new sequencer in, d/l'ed the schematic and manual for my model from Nordyne and followed it to the T. Installed new sequencer and the fan and heat were coming on as soon as power was applied from the breakers - would stay on until power was shut off. With power at the breaker off (leads still conected on sequencer) I checked for continuity across M1 and M2, M3 and M4 and was showing continuity across both but not across M5 and M6. So I thought I got a bad sequencer out of the box, called and got a new one sent right out. Meanwhile was controlling heat with breakers to stay warm and it was working fine, all coils getting hot.
Also replaced the t-stat with a digital model and replaced the fan relay (wanted a new t-stat anyway).
Got the replacement sequencer and went to put it in. Made sure power was off and pulled the leads off the sequencer that was currently installed, checked it with my meter and it checked ok - very odd I thought. So... I hooked it back up and turned the power back on - fan and heat coils did not come on right away as they had been, thought that was a good sign and sent a call for heat from the t-stat. Fan came on but only the third coil came on, checked for power off M1 and M3 while it was on, no voltage out of sequencer on those terminals. Thought, ok maybe it is a bad sequencer after all. Swapped it out with the 2nd new one and it is doing the exact same thing.
I have checked the coils, good contintuity (very low resistance), none of them are grounded. I've rechecked the wiring about 50 times to the schematic, all is as it should be.
Also checked the control from the t-stat, turns on and off by temperature control as it should, stays off when switched to off, a/c works normal.
Checked for 24volts across the sequencer - good.
What am I missing here? Surely I can't have two new sequencers be bad...
How do I check the limit switches? They are the self-resetting type.
Any guidance will be very appreciated, the wall is starting to look tempting to the noggin'....

Thanks! - Jeff

[jgolomb]

Meanwhile back on the ranch.... Talked to a friend in HVAC, was told to check the heat coils and limit switches.
Pulled the heat coils out (3 coils), cleaned them up and there are no problems - each meters about 12 ohms across from one end of coil to the other.
Metered the limit switches, they are closed as they should be with no resistance, also tested them while I had the coil assembly out with a heat gun, they open like they should and close again when cooled down.
Powered back up again and still have the same problem - no power to the first and second coils, coming off M1 and M3 respectively from the sequencer. Checked limits with power on and call for heat, still good with no resistance. I'm callin' the limit switches good.
Did some further metering with the sequencer - with nothing hooked up all terminals are open, the 24V connections show about 24ohms reisitance across. However, with ac leads connected to sequencer I get about 180ohms reistance across M1-M2 and also M3-M4. M5-M6 stays completely open. M1 also has a lead off it that goes to the connector 5 on fan relay. M4 has a lead to the com of the 24v transformer. This is correct according to the Nordyne schematic.
24V connections at bottom of sequencer only show voltage (24v) when t-stat calls for heat, as it should.
Almost forgot, when testing I have been letting it run for a few min each time to give sequencer plenty of time to operate.
So far, the furnace is still winning this battle - I swear it's starting to laugh at me, please help!

Jeff

[Robert]

Hi Jeff,

Go here to read about and pay my $20 fee if you want step by step email troubleshooting help:

http://www.mobilehomerepair.com/Order4b.html


Otherwise, I can give ya the basics, but it sounds like you have traveled that road a few times.

24vac from transformer to t-stat to sequencer bottom terminals. Common wire back from bottom to common on transformer secondary side.

120vac from breakers to M1, M3 and M5.


When the M's close, 120vac goes to left end of the 3 element coils.


120vac from breakers through limits and connected to far right end of the 3 element coils.


240vac across each element coil and 120vac to ground from each end when working correctly.

Wire from M2 to fan relay terminal 5.


Thanks,
Robert

[jgolomb]

Hi Robert, thanks for the reply. This is actually the first time I've ever looked at a furnace, just did a lot of reading.

Got a question about the basics you covered:
You stated 120v from breakers to M1, M3, M5 (assuming then M2, M4, M6 go out to left side of coils)
The schematic from Nordyne says the opposite: 120v from breakers to M2, M4, M6 - M1, M3, M5 out to left side of coils.
Which is it and does it matter? The sequencer is basically a series of relays, if so it shouldn't matter which way you go across from what I know about relays - they are non-directional. Is this not the case with these?
I only ask for support because I bought the parts from your store and I've got two of the same parts that are not functioning correctly straight out of the box which seems very uncommon.
What do you think?

Jeff

[jgolomb]

Final chapter to this story:
As it turns out, sequencers are indeed relays that work sequentially (took one apart), the M's do not matter which side faces what as far as in and out.
What does matter is this:
Inside the sequencer between the two bottom connectors is a round brass plate that holds the bi-metal contactor. The bi-metal contactor is a cup shaped thin metal disc that when heated up by the 24volts across the terminals flattens out. There are small plastic rods that hit this cup shaped disc, normally held up by the disc - these plastic rods break the connection between the M's, when the cup shaped disc flattens the rods move down slightly (approx 1/16in) and allow the M's to connect.
Where am I going with this?
The orientation of M1, M2, M5 on the replacement sequencer was not the same as the original. On the original M1 was at the top when installed, the replacement has it at the bottom. The wires that go from the coils to the M's are not very long at all, using the replacement sequencer made the wire going from M1 to the top coil a tight fit and was pulling a bit on the sequencer which was causing the bi-metal contactor not to function with the plastic rods to the M's correctly allowing them to make contact. That is why M1-M2, M3-M4 was not working but M5-M6 was.
I lengthened the wires giving some slack, reinstalled the sequencer and Viola!
Hard lesson, learned the hard way... Hopefully this will help someone down the road and be some tech insight about sequencers - tight wires from coils to sequencer will pull a bit on the sequencer and cause it to malfunction.
Man, I sure need a beer about now....

Jeff

[Robert]

Hey Jeff,

Nope it don't matter which side. IF wires are not long enough, make longer ones or turn sequencer around(may have to drill a small hole or two).


OR, just connect at M2 instead of M1.

Glad it's going again.


Just for the record for future reference, I do not own the store or the website, it belongs to Mark Bower.


Thanks,
Robert

[jgolomb]

Hey Robert!
Just wanted to say thanks for the help you did and continue to provide, in this post and in so many others that I read and learned a great deal from in what paths to follow for troubleshooting the beloved furnace. The service and help you provide here on your own time is certainly exceptional and not to commonly found these days.
Sure wish there were more out there like you in the declining 'service' industry!

- Jeff

[Robert]

Hi Jeff,

You're very welcome and thank you for the kind words.


Take care and best wishes,
Robert