Nordyne C3BA-036C-B pressure switch and short cycles

[gregor]

I've got two issues, maybe related, maybe not. The first is the 2 flashes on the control board indicating pressure switch open. I've checked the venting, and ordered a replacement pressure switch (arriving tomorrow). This happens periodically, especially when it's really cold out (sub-zero the last two days). I can re-set this by popping off one of the tubes to the switch, replacing it, and waiting a little while. Sometimes it takes 3 or 4 tries to re-start.

The second, and potentially bigger, issue is that the furnace cycles quite quickly. The burner will only stay on for a minute or so, and the blower fan not much longer than that before the upper limit switch opens, the burner shuts off, the draft fan kicks in, and then the whole thing repeats.

Are these two things related? Will replacing the pressure switch fix the short cycling?

I've tried a couple of things for the short cycles. I have a Ritetemp 8050 electronic t-stat, so I can't adjust the anticipator (doesn't have one). I've switched the fan control on the t-stat from AUTO to ON so that it will blow all the time - doesn't make a difference, because when the upper limit switch opens, it shuts the burner down, and the blower and draft fan run until the switch closes again. Had an hvac tech out in nov. who said that I didn't have enough vents throughout the house open. I have all of them open (15 in all) and still have the short cycling.

Any other ideas? Any help would be gratefully appreciated. The furnace has been running non-stop for a couple of days and it's not more than 58 inside.

Thanks,

Greg

[Robert]

Hi Greg,

Look on furnace facing for data sticker with furnace model number.

The model number you gave is your A-Coil model number.


Also, look at your t-stat manual if you still have it and read every line to see if it tells how to access the heat anticipator.

Digital t-stats differ from manual t-stats.



Thanks,
Robert

[gregor]

Robert

The t-stat manual doesn't say anything about it, but on their website it talks about not having anticipators - they have a thermistor instead. From the website: "These devices track the air temperature very well so no anticipator is necessary. Ritetemp thermostats are specified and checked at +/- 1F."

The furnace is nameplated Maytag. The only other model number I can find is PGF1RL080C16B. There's also a sticker that has the PGF number with the numbers 903070P. Is any of this looking familiar?

I've done a little more investigating, and I think that I'm not getting enough return air to the furnace. I have a ranch on a slab, downdraft furnace with supply ducts in clay pipe under the slab. There have been two additions to the house, with supply added to them (one a continuation of the below slab ducting, the other added ducting in the attic), but there are only the two original 10" diameter return ducts in the attic.

Greg

[Robert]

Hi Greg,

How much sq. footage did the additions add ?


Did you upgrade/enlarge your hvac units ?



That's probably the model number (first one), I'll have to look tomorrow and see if I have any data on it.



Thanks,
Robert

[gregor]

Robert

The additions added about 700 sq. ft. All were done by prior owners. Total sq. footage is now about 2300. The furnace and ac were definitely upgraded, probably when the additions were done (maybe 1996?).

Thanks so much for the assistance,

Greg

[Robert]

Hi Greg,


I would immediately upon upper limit tripping feel sides and even front of furnace for excessive heat.


If you do not feel it to be overly hot, then may just be weak contacts opening in the limit requiring a new limit.


Can you read a part number on the upper limit ?



Thanks,
Robert

[gregor]

Robert

It does not feel all that warm. I thought that the upper limit was supposed to be around 140F for my furnace, but not sure if this is correct.

There are a whole bunch of different numbers on the switch. I think the part number is 626446B.

Thanks,

Greg

[Robert]

Hi Greg,

Limit Switch # 626446 (L140*) can be seen and ordered through

PayPal from left side of page here :

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



Thanks,
Robert

[gregor]

Thanks, Robert. I'll give this a shot. Hope it's just the limit switch. Next stop the blower?

Count me in with the humbly grateful. I appreciate your help!

Greg

[Robert]

Hi Greg,

You're very welcome, happy to help.


Thanks for ordering.


Take care and best wishes,
Robert

[gregor]

Robert

No joy. The new upper limit switch had no effect.

Other ideas? I've checked the coils, they're not dirty or blocked, I have a new filter. The only other things I can think of is an under-performing blower motor and a general lack of return air.

Greg

[Robert]

Hi Greg,

The a-coil can appear clean when it's not. At this point though, it would be best to let an hvac tech diagnose it with needed tools/equipment/experience to find the problem and not buy unneeded components.



Thanks,
Robert