Lennox furnace: only wired single stage


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Old 03-29-17, 09:21 AM
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Lennox furnace: only wired single stage

Hi all

In a previous thread, I asked whether my furnace was 'behaving properly'-- it was letting temp drop 5-6 degrees before turning on (even though thermostat indicated it was calling for heat much earlier).

Well, I was sick last week and was freezing, so I called in a service. They took apart the thermostat and there was no battery. That said, once they put it back together, the furnace now kicks on before the temp drops even one degree from the setting--MUCH better. Suspect there was a bad connection in the stat itself...

They looked at the control board as well, and discovered that the furnace (while 2 stage) is only wired for one stage (the thermostat can only accommodate one stage).

I have a thermostat that I planned on installing after the heating season that will accommodate 2 stage furnaces, but I have to pull new wire (hence the wait). Here is my question: is there any reason to NOT wire the furnace for two stage? I am admittedly unversed in forced hot air, and am eager to learn more. I would think that two stage is supposedly 'more efficient'?

Appreciate any and all info on this. I hope to pull cable in the next month.

The furnace is a Lennox G60UHV-36A-070-06
 
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Old 03-29-17, 09:59 AM
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If pulling another wire is impractical or impossible, try this. You will need to set dip switch 2 to the ON position.
 

Last edited by skaggsje; 03-29-17 at 10:23 AM. Reason: added
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Old 03-29-17, 10:16 PM
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There is probably no "efficiency" to be gained by going to a two-stage operation but there IS often a significant increase in comfort from using the two-stage.

With the two-stage the furnace will fire at about 60% of its ultimate output making longer periods of time while running and this along with the lower temperature air being circulated makes for a more even temperature throughout the house. Note that while it runs longer it burns fuel at a lower rate making the actual fuel burned the same over the course of the day or heating season.

The second stage will only cut in IF the temperature does not rise sufficiently during the operation on the first stage. Some multi-stage thermostats will energize the second stage after a period of time running on first stage and not achieving the set temperature.

My system, using a Robertshaw thermostat, will cut in the second stage if the first stage has been running twenty minutes without reaching the set point. The only time this happens is when I first turn up the thermostat (from a lower setting) and it is relatively cold outside. Most auto-setback thermostats will have a function that holds it in first stage for a longer period of time on automatic (end of night setback) operation.
 
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Old 03-29-17, 11:35 PM
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Your furnace may actually be running in two stage even with a single stage thermostat. It changes by itself based on firing time.

In the diagram is the heating DIP switch.
Switch 1 off=two stage with two stage thermostat on=two stage with single stage thermostat.
Switch 2 off=10 minute delay from stage 1 to 2. on=15 minute delay from stage 1 to 2.
Switch 3 and 4 don't get changed.

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Old 03-30-17, 08:53 AM
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fascinating! I need to look at those DIP switches.

So, I know the thermostat in use had an issue (seems to be resolved...for now...) so I am definitely leaning toward replacing it. This is the thermostat I have sitting on a shelf

Would this be a fair assessment:
  1. Best option: pull a wire and run with two stage thermostat
  2. Acceptable option: replace stat with another single stage and leave furnace running in 'dumb 2 stage mode' via DIP switch
?
 
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Old 03-30-17, 09:13 AM
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If you can pull a new wire ,that is your best option. Have you checked behind the stat to see if you have a spare wire ?
 
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Old 03-30-17, 11:00 AM
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Yes, I am sure. Its only 5 conductor / all used. I need a C wire and the W2/Y2
 
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Old 03-30-17, 03:19 PM
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If pulling wire is a major job you might consider the Honeywell Redlink line of thermostats.

You can get a Honeywell EIM and a Redlink TH8321R stat and run up to 3 stages of heat and 2 stages of cooling using only 2 wires to the thermostat.
(It is the same EIM that the Prestige uses and wires up the same.)

This option would require a separate internet gateway if you wanted to add "WiFi" access.


A step up would be the Honeywell Prestige IAQ. It can control up to 4 stages of heat and 2 stages of cooling using only 2 wires between the stat and the EIM.

 
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Old 04-22-17, 11:07 AM
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Hi! So I'm finally tackling this.

One thing I noticed: the dip switches are not located where shown on diagram

They are on the right. There are only three

Currently, they are off-on-on

There is a jumper below it for single or double. Do I need to adjust that?

 

Last edited by PJmax; 04-22-17 at 11:22 AM. Reason: repaired link
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Old 04-22-17, 11:30 AM
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Look on the back of the blower door for further info.

Otherwise post the model number of the board.
 
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Old 04-22-17, 11:48 AM
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I think it's an ANSI z21.20?

Sure litetwo stage variable speed. White Rodgers


I see a white sticker that says 50U61-120-04
 
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Old 04-22-17, 11:59 AM
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Old 04-22-17, 12:13 PM
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Interesting.

It does seem that I have to move switch E20 to use dual stage thermostat. I can't tell if this person has same unit as me, but the switch E20 popped on a search

Lennox furance will not turn on. The fan will not even turn
 
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Old 04-22-17, 12:40 PM
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There are 3 pins. The jumper goes in 1 of 2 places.

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Old 04-22-17, 12:48 PM
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That's what I was thinking. I will be wiring for two stage heat/ one stage cool. I believe I need to more his jumper to the other position for the furnace to anticipate two stage thermostat?
 
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Old 04-22-17, 12:56 PM
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Yup.... that is correct.

I was still trying to straighten out the 3 position vs 4 position DIP switch issue.
The service manual says 4 and yet the board is 3.
The online service manuals aren't always the most up to date.
 
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Old 04-22-17, 01:12 PM
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Thanks! So, the HVAC guy advised me, if I wired a two stage thermostat, to put a jumper, at the board, for Y1/Y2, as the wire from the splice in the basement to the control board is only 6 conductor.

I assume this is required now as that jumper would cause the furnace to expect something tied to Y2 when set to two stage?

Initially, there was nothing connected at the board to Y2
 
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Old 04-22-17, 02:19 PM
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We were discussing heat. Are you now asking about two stage A/C ?
 
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Old 04-22-17, 02:33 PM
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I apologize for any confusion.

I am wiring my multi stage Lennox furnace to a new thermostat that is capable of multi stage control

My question was to confirm the need to connect a jumper from Y to Y2, as the HVAC tech suggested when he was out diagnosing our system no functioning properly

I am not trying to change the subject--just want to ensure I am wiring this properly. There was no connection to Y2 with the old stat

One other question: how doe I test that the new stat is properly controlling the two stages?

I see two LEDs that start blinking furiously when the heat is on... then blink slowly after something "clicks" at the furnace (maybe it reached temp at the stat?) but the fan is still on. Would this indicate whether stage 1 or 2 is running?
 

Last edited by sirk98; 04-22-17 at 02:37 PM. Reason: One more question
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Old 04-22-17, 02:37 PM
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You can change the subject. Just wanted to make sure you were discussing A/C now.

For two stage operation you would have two wires from stat to compressor. Y1 and Y2. No jumper.

I'm not exactly what two stage is for your unit.... possibly dual compressor ?
 
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Old 04-22-17, 02:44 PM
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Hi! I also edited my last post and added a question about testing the stat...

Regarding the AC:
I think I have been told its two stage as well--not sure how to test. But I am running it as single stage. My thermosat wire has two segments:

Segment 1: runs from stat to a splice near furnace

Segment 2: runs from splice to furnace

I replaced ONLY segment 1. As I ran 8 conductor, I DO have capacity to connect Y2 from stat to the splice, but I did not. The reason is Segment 2 is only 6 conductor--I needed those two for the C and W2.

So, stat is in two stage heat / one stage cool mode. The clarification I was seeking was because there was NOTHING connected to Y2 when I started this work, but I now have a jumper on it--based on HVAC guy's recommendation

I really appreciate the replies, btw! Thank you!!
 
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Old 04-22-17, 02:54 PM
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FYI
In staring at the board, it looks like there is a place for dipswitch 4-- it's just not there. 1-3, didn't adjust. OFF-ON-ON

That jumper is labeled E20-- I did move to two stage

I see dip switches 5-12 above the CFM light. Didn't touch them/don't know what they are for

This is very educational
 
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Old 04-22-17, 07:10 PM
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You need the Y1/Y2 jumper because your outdoor unit is single stage (or at least that's how it's wired). If you only connect the yellow to Y1, then the fan will run slower than it needs to, potentially causing your A-coil to ice up (since the outdoor unit is running at max) when it's really humid but not so hot out. It's basically there to trick the control board into running the fan at high speed for all cooling calls.

Can you give us the model number of the outdoor unit? How old is it? If it is in fact a two stage unit I'd be pissed at whoever installed it because they've been costing you a lot of extra money on your power bills.

Is there a reason you only reeplaced one part of that cable? You really should've run the new cable all the way from the stat to the furnace.
 
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Old 04-23-17, 07:20 PM
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Thanks for reply!

I need to get outside and hunt down the model number.

I need to buy more cable, then I can complete the run from splice to control board
 
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Old 04-23-17, 07:35 PM
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You really shouldn't have a splice. It should be a single continuous run from the stat to the control board. then anything else that needs to be spliced in (like the outdoor unit, a humidifier, etc) should be connected to the control board terminals. So make sure you buy enough to go from the stat to the furnace.
 
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Old 04-24-17, 08:57 AM
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ugh. This makes sense. I just based this off my previous house (had a splice above boiler) and this house also had the wire spliced. I assumed that was 'best practice'

I have no desire at this point to redo the job with longer cable.

I will get back to this thread once I have model info from AC unit to see it I need to complete the run to make the AC two stage controlled as well

Thank you all so much for the help! I wouldnt have attempted this job without knowing about these forums. Really helps with the initial confidence factor! (knowing there are helpful experts out there when I run into problems, I mean)

 
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Old 05-19-17, 12:45 PM
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considering 'finishing the job'

Hi all,

Sorry for the delay. So, where we left off:
  • Furnace working beautifully wired as two stage
  • AC appears to be wired single stage

Wondering if I will get the same difference in terms of comfort improvement if I wire the AC to leverage two stages. Today, its pretty hot. Some rooms are quite cool, others (split level) are more toasty.

The request (below) was for the AC model info, here it is:


So, I have conductors in the wall, I can run Stat Y2 to splice. I can then replace the wire from the splice into the furnace control board so I have adequate conductors to go Y2 (at splice) to Y2 on board.

Are there other changes required?

Thanks so much for the help!
 
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Old 05-19-17, 05:08 PM
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If you have a split level home that was ducted for heat.... your single A/C will never cool the house evenly.

The only real way is to open the walls in the second floor and add high registers above the low ones. In the summer you open the high registers and close the lower ones. Opposite in the winter.

Secondly you need high returns to draw the heated air from the second floor ceiling. Due to the size of the ductwork needed..... this is almost impossible.

One reason why attic insulation is so important.

Looking at the service manual....... there is no second stage in that A/C condensor.
Lennox/HSXA15-HSXB15.pdf
 
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Old 05-20-17, 08:14 PM
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your a/c is not a 2-stage but is a nice unit, better than what's available today.

it's a myth that you can't cool two stories properly with one system provided it was ducted right, for whichever needs more air.

High level returns are necessary but you don't actually need high level supplies. as long as the supply has enough velocity to mix properly and you have returns pulling the hot air from near the ceiling it can work.

maybe not perfectly, you'll still see a 2 to 3f temperature difference, but good enough.

central air has trouble with 2 stories on one zone often because of lousy ductwork and/or unbalanced loads. (like where the main floor windows get shaded more so it cycles off, upstairs gets hot)

done right, it can work.
 
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Old 05-21-17, 03:14 PM
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provided it was ducted right, for whichever needs more air.
Correct.... but an old heating system was not designed to cool adequately. I know first hand in my split level home. The heating is very even. The A/C is lacking on the second floor.

Most split level homes don't allow for additional high return installation. I know mine doesn't.

My house was built in 1959.
 
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Old 05-22-17, 10:35 AM
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thanks for the replies!

Yes. All the supplies/returns are low on the wall.

There is a supply in the dining room that is the first supply once leaving the blower/furnace. I was playing with 'balancing' the system and closed that return--trying to get more air to the 2nd story.

After a few hours running set like this, I noticed that the thermostat (directly across the room from the supply) was showing setting 74, temp 78 in the dining room. I opened the supply 1/4 open, and it quickly dropped to 74 and turned off. It also WAS warm in that room. The second story was toasty as well (76/77 when the AC hit target 74).

This is why I was wondering if I needed to wire for two stage (thank you for resolving that for me!). FYI: I did upgrade attic insulation last fall with blown in cellulose.

@muggle: wondering what makes this AC much better than current ones? Always looking to learn!

Thanks, all!
 
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Old 05-25-17, 08:39 PM
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Lennox used to put the compressor in a separate insulated compartment. quieter and everything accessible for service. Large, low rpm fan too.

now they build them cheaper and it's under the fan. Smaller fan. suspect every brand has cut corners and it's a real shame.

Your unit uses the current refrigerant 410a and exceeds present efficiency standards but has the good build quality/design of older equipment. best of both worlds; don't part with it even if it needs a expensive repair, it's a really good machine.


to get better cooling on the second floor you would have to fix ductwork. without high level return you will always have trouble cooling second floor.

balancing should help.

another strategy if you have enough supply upstairs is having the cooling thermostat on the second floor (via remote sensor) and closing vents on the main floor until both are comfortable.

only works with generously sized ducts.

Heat rises which masks a lot of problems with ductwork; hence being okay in heat mode even if the second floor lacks sufficient airflow.


Well engineered ductwork will be sized based on room by room load calculation. and if cooling cfm required for a room is greater than heating or vice versa, the size gets bumped up and you damper down for the mode of operation which needs less.

Ductwork has to be engineered for ac, add it to an older house which wasn't designed for it and there will always be issues doing the second floor.
 
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Old 05-26-17, 07:08 AM
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wow! the one thing going for me on this house

thanks for the info--I'll defintely lean toward repair for any future issues

THe issue with cooling: basically I saw the AC was running pretty much all the time if I had the supply in the dining room (opposite thermostat) closed fully. Hoping things arent undersized or anything like that...

I have to play with balancing...
 
 

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