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wells

@sonic.net

Single stage thermostat for a two-stage gas furnace?

I recently replaced my broken old thermostat with a new one (LUX TX1500E), and my gas heater (Trane XL-80) is now blowing cold air most of the time.
I noticed that on the heater's control border, the two contacts for wire W1 and W2 are connected with one wire.
Does this mean that the furnace has been wired to run on single stage, and as such, I should use a single-stage thermo?
Also, I noticed that the heater will give hot air when the temperatures between the room and the desired one on the thermo have a large difference.
Thanks.



cdru
Go Colts
Premium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:7

said by wells :

I noticed that on the heater's control border, the two contacts for wire W1 and W2 are connected with one wire.
Does this mean that the furnace has been wired to run on single stage, and as such, I should use a single-stage thermo?

With W1 and W2 jumpered, the first stage will always run for the first 10 minutes of a call for heat. Calls longer than 10 minutes will then switch to the 2nd stage. IF you get a 2-stage thermostat, remove the jumper and hook W1 and W2 to the thermostat's W1 and W2. The thermostat will then be in control of when the 1st and 2nd stages are used.

Also, I noticed that the heater will give hot air when the temperatures between the room and the desired one on the thermo have a large difference.

When there is a larger difference it means that it will probably run longer, switching over to the 2nd stage. You probably are feeling the hot air during the 2nd stage because it's hotter. If there is no heat for the 1st stage, you may have a problem with that. Or you just think it's not hot but it's sufficient for the majority of your heating needs for your location except the coldest days.


pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Reviews:
·Comcast

2 edits
reply to wells

Did the XL-80 blow cold air before you switched thermostats? Or is this a new problem and there is possibly a wiring problem or configuration problem with the thermostat?

Most new thermostats can be configured for a lot of different systems, gas/oil furnace only, furnace and Air Conditioning and heat pump with aux/emergency heat. Make sure the thermostat is defined for the type of system you have.

On the XL-80 there is a jumper on the board and dip switches that can control the second stage starting times. I don't have the service manual in front of me but they are marked on the wiring diagram on the inside of the cabinet. (edit) they are S1-1 and S1-2. The staging works as follows: a heat call goes to W1 terminal. If the thermostat is not satisfied before the onboard timer times down, the second stage will start and both stages will run until the thermostat is satisfied. This is the preferred way that MOST systems are setup if there is not a true 2 stage thermostat inplace. The advantage of this is more even room temperatures and some fuel savings.

The way you are wired, both stages should fire immediately.

It sounds like the igniter may not be working and the system is shutting down on a safety. Look in the little window on the side of the furnace and see if there are any codes showing from the blinking red light on the board.
--
The difference between genius and stupidity is that genius has its limits.



nunya
Premium,MVM
join:2000-12-23
O Fallon, MO
kudos:12
reply to wells

Call me mr obvious, but could it be the fan is stuck on (either switch or miswired).
--
If someone refers to herself / himself as a "guru", they probably aren't.



cdru
Go Colts
Premium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:7
reply to pende_tim

said by pende_tim:

On the XL-80 there is a jumper on the board and dip switches that can control the second stage starting times. I don't have the service manual in front of me but they are marked on the wiring diagram on the inside of the cabinet. (edit) they are S1-1 and S1-2. The staging works as follows: a heat call goes to W1 terminal. If the thermostat is not satisfied before the onboard timer times down, the second stage will start and both stages will run until the thermostat is satisfied. This is the preferred way that MOST systems are setup if there is not a true 2 stage thermostat inplace. The advantage of this is more even room temperatures and some fuel savings.

The way you are wired, both stages should fire immediately.

The way you describe it seems to be different than what is described here on page 15. Either there was a design change for the XL-80 line, or one of us isn't looking at the right manual.


pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Reviews:
·Comcast

1 edit

The manual I have shows a different wiring diagram. For 2 stage with a single stage stat, it shows no jumper, no note on w1-w2, and calls out the S1 switches.
"Design Features Subject To Change Without Notice".

The OP should pull the cover and look at his furnace.

Here is the one I found, see page #16: »www.bayareaservice.com/wp-conten···nual.pdf

Here is the wiring diagram showing S1 1&2 settings on page #6: »www.bayareaservice.com/wp-conten···acts.pdf

This one is a -24 rev and the one you found at munch is a -22, so they could have changed.

I do recall reading somewhere else that some high efficiency furnaces blowing cold air and then coming on much later is a sign the furnace needs some kind of service. IIRC from the discussion, , the furnace will blow air for a long time then try a restart. If successful, it will produce hot air and continue the heating cycle. This feature somehow is a warning to the homeowner that service is required. Like I say, I only read this and have never seen it occur.
--
The difference between genius and stupidity is that genius has its limits.



cdru
Go Colts
Premium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:7

said by pende_tim:

The OP should pull the cover and look at his furnace.

Here is the one I found, see page #16: »www.bayareaservice.com/wp-conten···nual.pdf

Here is the wiring diagram showing S1 1&2 settings on page #6: »www.bayareaservice.com/wp-conten···acts.pdf

This one is a -24 rev and the one you found at munch is a -22, so they could have changed.

Hopefully there's a wiring diagram on the furnace that can straighten it out. From the differences in the two manuals, it looks like there might have been a control board design change so that some operation parameters can be set by the dip switches. If there aren't any dip switches...


wells

@sonic.net
reply to wells

Thanks for all the replies.

I read the installation manual for LUX TX1500E again, and it said:

"This thermostat can be used with most single stage 24 volt: gas, oil or electric heating and/or cooling systems, single stage heat pumps, or gas Millivolt heating systems. It cannot be used with 3-wire zone valves, 120 volt heating systems, or multi-stage heat pumps. ..."

Does this --- the last sentence "It cannot be used with ... multi-stage heat pumps" --- mean I have used the wrong thermostat?

My heater had been working perfectly before the change of the thermostat.



pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Reviews:
·Comcast

Yes it can control a 2 stage Furnace if the furnace handles the upstaging from W1->W2

Ok lets take a step back.

Why did you replace the old thermostat? Was there a problem?

Can you post a picture of the thermostat wiring?

Do you have an Air Conditioner compressor/coil in the furnace in addition the the gas furnace? In other words is there a "Y" wire connected?
Do you have a heat pump? There would be a Y wire as well as a O/B wire?

Is the LUX new? This is a very old model and it is possible that it is defective.

The quickest way to test the system and isolate the problem would be to turn on the furnace's fan manually using the LUX and carefully move the wire on the W terminal to either of the R terminals. The Rc and Rh should be jumpered. This will force the heat to come on and verify the wiring between the thermostat and the furnace. If the heat comes on immediately, the problem is with the thermostat and it should be replaced. If it does not come on, the problem is with the furnace wiring or the furnace itself.. Try getting a Honeywell that will do 2 stage heating if there is an extra wire between the thermostat base and the furnace terminal strip. This wire will be used for the W2 connection. They are not too expensive and will give you better comfort and !economy ! than the timer control in the furnace.

Let us know and we can help you from there.
--
The difference between genius and stupidity is that genius has its limits.