Honeywell MagicStat thermostat -> questions about jumper settings on the back

HVAC Guy · 2011-12-29T14:52:33+00:00

I've got a Honeywell MagicStat thermostat that has 2 jumpers marked as"A" and "B" that are opened or closed by a screw head that you tighten(to close the jumper) or turn out (to open the jumper). There are 2 other jumpers (C and D) - C is to set Celcius orFarenheight, but I don't know what "D" is for (there is no screw forthat one - so it's open). I can find no reference anywhere what D couldbe for.I'm not quite sure what exact model of MagicStat I have - there isabsolutely no number or name stamped or printed on this thing. Not eventhe word "MagicStat". I've seen models like 28, 1000, 2800 and 3200from web searches. I believe this one was purchased between 1996 and1999.This is the most similar picture I could find of the front panel: this is the best picture for the entire unit: thermostat is controlling a 20+ year-old GE "Whisper-heat" naturalgas furnace. This is NOT a high-efficiency (or condensing) furnace, butit does have an electronic control module, combustion damper gate andelectronic ignition.The furnace is cycling too often to suit me, and so I'd like to know ifthe thermostat can be modified to solve that.The written documentation for the A and B jumpers are as follows: Warm Air Furnace: Set at the Hot Water setting (A-out, B-in) Electric furnace: Leave at the Warm Air Furnace setting (A-in, B-in)(the way the second line reads is confusing)It also says: For high efficiency (>90% AFUE): A-out, B-inOn the back of the unit these instructions are stamped into the plasticcase: Warm Air Furnace: A-in, B-in, Fuel Switch F Hot Water Boiler: A-out, B-in, Fuel Switch F Electric Furnace: A-in, B-out, Fuel Switch EOn my thermostat, the current settings are: Warm Air Furnace: A-in, B-in, Fuel Switch FI believe that the only thing the Fuel Switch does is turn on the fanwhen heat is called for (in the E setting) otherwise the fan is turnedon by the furnace (in the F setting).So if anyone knows, I'd like some clarification as to how exactly the...

Dec 29, 2011 28 Replies

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Steve 14 years ago

Yup... big box store junk..... There is a sucker born every minute that will buy one.

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Grumpy 14 years ago

degrees, it is how this stat (RTH221) seems

expected, but when set to 3 or 1 CPH in my house

hours to adapt. I have a 90+

times per hour.

reading would swing from 58° to 65°

******************************************************************** Ok enough of this crap apparently your cheepy Tst is much more sensitive

Than the others, to make it more stable you can cover Tst with something

To see how much of effect will have, or/and if you have forced air heating

Make sure that your duct discharge is not blowing on to Tst.

********************************************************************** with each cycle while 3 other

thermometer, and an indoor/outdoor thermometer

show the swing as being from 61-63°.

reading quickly dropped to 61° and stayed

show 61° as well the RTH221 dropped to

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Daniel who wants to know 14 years ago

That's what I thought at first so I wedged some plumber's putty in the corner where the thermistor is located (it sits epoxied into a small recess in the bottom left corner of the plastic housing) to add thermal mass, this showed no change. Besides have you seen how fast a meat thermometer reacts to temp changes? In air it only takes a few seconds per degree for a small change, in meat they don't call them "instant read" for nothing.

I thought about also putting a clear storage bowl or one of those anti-tamper plastic boxes over it.

Nope, the supplies are on the other side of the room.

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The Daring Dufas 14 years ago

I'm afraid I didn't follow this thread that closely but did anyone mention making sure any holes in the wall behind the T-stat were sealed? That would be the first thing I always look for. I've found that even the tiniest holes can let in enough air to screw with an electronic sensor. Even air getting past/through the little plastic anchors for the mounting screws. o_O

TDD

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Daniel who wants to know 14 years ago

In my case that is covered too, the thermostat is mounted to a paneling wall of the closet that the furnace is in, the walls are bare studs inside the closet, and the furnace is direct return instead of ducted with 2 20x25 filters in an A frame shape on top (it is a downflow), IE the area behind the thermostat is conditioned space.

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