Multistage York Furnace with a Honeywell TH9421C1004 thermostat

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Old 11-20-11, 01:22 PM
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Multistage York Furnace with a Honeywell TH9421C1004 thermostat

I have a new dual fuel York 2 stage gas furnace/York single stage heatpump running on a Honeywell TH9421C1004 VisionPro themostat. I began having furnace problems the minute the installers left. It turns out there is a known issue with certain York furnaces run by Honeywell Thermostats where the fan will not come on when the thermostat calls for auxillary heat (in my case the gas furnace) - ( http://hvac-talk.com/vbb/attachment....1&d=1288030266 ). When the gas furnace came on the system would shut down with an overheat error. The supposed solution was to replace the main control board with a new (updated firmware) board.

The contractor did that but he also set the thermostat for a single stage gas furnace and then set the furnace board to control the second stage (comes on now after a certain amount of time - 15 minutes). He told me that the system would work better - he didn't trust the updated firmware.

My question now is which is better - to have the second stage heat controlled by the thermostat or by the furnace? Or does it really matter? It is currently running fine - heat pump comes on in the morning, 30 minutes later the first stage gas comes on, 15 minutes later the second stage kicks in (assuming the house hasn't reached set temperature first...). I want to know whether it is better (or more efficient) to have the thermostat control second stage heat. Thanks.
 

Last edited by ramsey248; 11-20-11 at 02:18 PM.
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Old 11-20-11, 05:15 PM
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How much detail do you want in my answer?
 
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Old 11-20-11, 06:06 PM
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As much as you are willing to give me... Thx.
 
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Old 11-21-11, 11:15 AM
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I'll write more in a couple of hours. Need to feed my face right now.
 
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Old 11-21-11, 04:31 PM
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The letter from York you linked to describes a specific problem with the control board not properly responding to receiving a simultaneous first and second stage heat call. This would apply to not just Honeywell thermostats but also to any other brand that did not have an internal timer separating first and second stage heat calls. I suspect that the new control board has addressed this fault by incorporating its own internal time delay.

To go into more detail concerning staged heating...

Staged heating with a gas furnace (without your heat pump, I'll address that later) is not really done for efficiency as much as for comfort. The difference in combustion efficiency (NOT system efficiency) between the two stages is minimal but the longer the furnace runs the greater will be the comfort level in the house. There is some efficiency gain due to reduced start/stop periods but mostly it is comfort due to more even temperatures throughout the home. To this end a two-stage thermostat will ALWAYS be better than using a timer to actuate the second stage.

Most multi-stage setback thermostats have an internal subroutine known "adaptive recovery" or some other proprietary name. This adaptive recovery routine "learns" the characteristics of the particular heating system and then adjusts the time when the system starts to "recover" to the daytime occupied temperature setpoint. In other words, when a person programs the thermostat they set the time they desire a specific temperature and the thermostat calculates how much earlier it needs to start the furnace at the lowest heat output to achieve that temperature at the correct time. This keeps the furnace blower in a lower and more economical speed, reduces noise and heats everything slowly and gently. If the thermostat senses that the proper temperature will not be achieved at the proper time it will energize the second stage shortly before the appointed time. It is easy to see that basing the second stage on just a running time could cause the second stage to energize just seconds before the entire furnace shuts down and THAT is to be avoided if possible.

Now with a heat pump it is a bit different. Heat pumps generally discharge lower temperature air than do combustion furnaces so the time to raise the temperature in the house is proportionally longer. Using deep setbacks with a heat pump is generally not a good idea because the recovery time is such that it causes the secondary heat source (usually electric heaters) to be energized and that action tends to erase any economical advantage offered by the heat pump. In your particular case that is not entirely true since your secondary heat source is from a gas-fired furnace but you still want to try to reduce the usage of the gas in favor of the heat pump. Having a thermostat with adaptive recovery along with specific timing before allowing the second (and in your case, the third) stage of heating makes a great deal of sense.

Depending on how the thermostat is wired to the furnace and heat pump (and how many wires are in the cable) you should have the ability to have a well controlled three-stage heating system. My personal opinion is that your heating contractor either does not have the expertise to properly set up your system or just plain doesn't care.
 
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Old 11-22-11, 07:37 AM
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Thank you for the great response - you have helped clear up several issues for me. Based on your information, I am going to change the setup - make the thermostat run 2 stage and disable the 2nd stage control on the furnace board.

Please explain something for me... When (and how) does the thermostat call for W2? Is it as a result of a large temperature difference (like after a setback) or is it timed (comes on if the temperature rise is not fast enough) or both? And, should I add a timer to W2 (3 minute 24 volt timer) just in case the York board still has an issue?
 
  #7  
Old 11-22-11, 11:34 AM
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Different thermostats have different methods of not using the second stage during a programmed return to higher temperature event.

When the thermostat is being operated in manual mode or during an "occupied" (for want of a better term) period in programmed mode the second stage is controlled by a set differential lower than the operating setpoint.

(I know that might be hard to understand for most people without a controls background so I will give some details.)

As an example I will use my settings. I have a Robertshaw programmable thermostat although since retirement I maintain a "variable schedule" () and run it manually.

My second stage is set to "cut-in" three degrees below the first stage set point. This means that when I manually set my temperature to 70 that the furnace only runs on the first stage unless the room temperature drops to below 67. That would only happen if the weather was such as to drop the outside temperature something like fifty degrees AND blow off the roof of the house so the furnace never goes to the second stage during normal operation.

I manually set the temperature down to about 64 before going to bed. In the morning I manually turn it up to 68. If the inside temperature has dropped to below 65 then the second stage does cut-in and I get full output from my furnace and the house warms up to the setpoint (68) faster than if the furnace was running on just the first stage. After that initial warm up the furnace never again runs the second stage because the thermostat is set to maintain temperature within one degree. MAYBE if it was 50 below zero outside the heat loss from the house would be such that even with the furnace running constantly it couldn't maintain set point, the inside temperature would drop the requisite 3+ degrees and the second stage would cut-in.

In full programmed mode my particular thermostat "learns" the characteristics of the house and heating system. It "knows" how long it takes to raise the temperature from the night setback to the morning setpoint and it calculates when to actually move to the morning setpoint so that the morning set temperature will be achieved by the programmed time. This is the "adaptive recover" I previously mentioned. This feature is one of the most important in the evolution of the programmable thermostat. In older clock-thermostats the user had to try to determine when to have the thermostat change from night mode to day mode (they only had two setpoints back then.) so that the desired temperature was achieved at the proper time. This meant that most of the time the change came too early or too late.

Part of the adaptive recovery is that the "brain" of the thermostat will monitor both the time and the room temperature and if it senses that the programmed temperature will not be achieved at the programmed time then it will enable the second stage. In my thermostat this is done during the 20 minute period before the programmed time although different manufacturers may use different time frames.

So, for most thermostats a programmed temperature change will NOT allow second stage operation until a short time period before the programmed time for a specific temperature but manually changing the setpoint upwards more than the programmed differential WILL cause second stage operation.


Also keep in mind that your furnace is likely oversized for your house, most are. Even if it is correctly sized the sizing is based upon the coldest weather ever experienced in your area and probably contains a "fudge factor" just to be certain. That means that in all but the coldest weather the furnace is oversized and perhaps hugely oversized. In normal operation using a two-stage furnace with a two-stage thermostat means the furnace will never go into the second stage but might fire for longer periods of time. The result is more even heating and less wear-and-tear on the furnace from alternate firing and non-firing periods.

I would not add any timer to the control board UNLESS there is still a problem.
 
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Old 11-22-11, 02:17 PM
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Thanks again. This makes sense and explains some of the behavior I am seeing... Do you have any idea what the temperature differential is for this Honeywell thermostat (the difference in temperature used for 2nd stage cut-in)? I understand "droop" (currently set to 2 degrees) but if I read the manual correctly, that is used, as you point out, when the temperature in the house goes down while the furnace is running (your "blow the roof off"...).

What I want to happen is exactly as you describe - in the morning, after setback expires, if the temperature differential is greater than X degrees come on with 2nd stage heat otherwise heat pump/first stage.
 
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Old 11-22-11, 02:20 PM
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I am not familiar with your thermostat but ALL parameters are adjustable if you have the installation manual. You might want to post the question in the thermostats and controls forum at the bottom of the category page. Jay knows more about those thermostats than Honeywell.
 
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Old 11-23-11, 10:19 PM
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FWIW, I have a York TM8V 2-stage furnace and a VisionPRO IAQ thermostat. I have not had the blower problem, and my installer did not change the control board. I have also tried a jumper on W1 to W2 and had not problems.

I also checked the signals from the EIM. With a large difference between setpoint and indoor temperature, W2 does not come on immediately. There is about a 50 to 60 second delay between W1 and W2.

I think there is more to this story than what was in the York memo.
 
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Old 11-25-11, 10:33 AM
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Multistage York Furnace with a Honeywell TH9421C1004 thermostat - resolved

Thanks to everyone for the responses and help. I am posting this follow up in case somebody else has a similar problem. I should point out that my furnace is a York TM9V.

I have set the thermostat to control the furnace stage 2 instead of using the furnace board. This morning I was standing in front of the furnace when the setback expired and discovered two things. One - the delay from initial heat request for stage 1 and the fan start (variable speed fan) is about 20 seconds. And Two - the delay for the second stage start from the initial heat request is about 17 seconds. This means that the system has not started the fan before the second stage request is made. This trips the rollout switches... There is no problem with the unit if the fan is already running...

I am going to install a delay on make timer onto stage 2 furnace heat to address this (30 seconds should do it). Apparently the new board from York did not fix the issue completely...
 

Last edited by ramsey248; 11-25-11 at 12:38 PM. Reason: resolved
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Old 11-28-11, 02:47 PM
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ramset248 -

FWIW, the information I have shows that the TM9V and TM8V use the same control board.

Now that you mention the timing again, I think I did my timing experiments with a Prestige IAQ. I'll repeat it with the VisionPRO IAQ I'm runing now. I have the one with the EIM.

As I mentioned before, I jumpered W1 and W2 and did not have a problem. So, I think it's a problem with timing, but NOT a simultaneous call for W1 and W2.

This is very interesting if you got a replacement board and it has the problem. Is your VisionPRO the one with the EIM?

Also, there's a 6-digit number printed on my board (near the top, center). If you can find it I'd like to know what yours is. Mine is 449572.

BTW, I think an ICM104 would work for your delay. I have one but didn't use it (yet). Pexsupply.com or ControlsCentral.com
 
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Old 11-29-11, 08:57 AM
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Update - test results

ramsey248-

I had based my earlier assumption that my furnace did not have the problem on test results with the Prestige. I did some testing last night with the VisionPRO and was able to produce the problem as reported by you and by York.

I didn't get exact timing, but it was about 30 seconds after the initial call for low stage heat when the VisionPRO EIM called for high stage. The fan failed to start. For now I'm running on the furnace upstage timer, set at 20 minutes. We don't use nighttime setbacks, and the furnace is moderately oversized, so in our case it doesn't make much difference. The only time we went over 20 minutes on low was last year when we had record low temp (this was a 30-year record). I may use the delay-on-make relay, but I'm not sure it's worth the effort on my system.

So, it IS the timing of the W1 and W2 calls, but it's not simultaneous as some have reported. The problem is the stat calls for high heat (W2) just before the control board would start the fan, and apparently this confuses the control board and it does not start the fan at all. With the VisionPRO, this is maybe 20 to 30 seconds. My earlier testing showed the Prestige energized W2 at about 55 to 60 seconds, explaining why it worked fine with that stat.

If Jay reads this maybe he has additional comments.
 
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Old 12-02-11, 04:01 PM
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Thank you so much for the effort. I was beginning to think I was doing something wrong and/or had a unique problem (or was nuts). Anyway, I have not had the problem since I put the timer on the system (extremely simple to install).

To answer your question, I do have an EIM. I happened to be standing at the unit the other morning with a meter and was able to capture details as the unit fired. I am convinced, as you are, that the issue is timing based and therefore the timer "should" address the problem.
 
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Old 12-02-11, 04:20 PM
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I just checked the board number - next to the bar code - 642768. I don't see any revision number on the board or any other identifier.
 
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Old 12-02-11, 09:50 PM
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Originally Posted by ramsey248 View Post
Thank you so much for the effort. I was beginning to think I was doing something wrong and/or had a unique problem (or was nuts). Anyway, I have not had the problem since I put the timer on the system (extremely simple to install).

To answer your question, I do have an EIM. I happened to be standing at the unit the other morning with a meter and was able to capture details as the unit fired. I am convinced, as you are, that the issue is timing based and therefore the timer "should" address the problem.
I'm curious how you wired the timer, and what timer you used. I was going to use a ICM104 and drive the coil (input) with the W1 signal and connect W2 on the output terminals. That way, it acts as a "W2 inhibit" for the time delay. So, W2 is not always delayed, just not allowed to connect until W1 has been on for a while (maybe 1 to 2 minutes). You could also just put the delay on W2 alone, but that does an unnecessary delay if W1 has been on for a while.

BTW, using a different brand as York recommended would NOT also work. If you happened to bump up the setpoint at the wrong time, the same problem could occur. The timer is the only real fix, for now.
 
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Old 12-03-11, 01:52 PM
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I used a Supco TD69 connected directly to W2. I live in the south (North Carolina) and doubt it will ever get cold enough to force W2 on while W1 is running. If it does happen though I don't think the few second delay I have set on the timer will make much difference...
 
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Old 12-03-11, 02:39 PM
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Thanks for the info on the TD69. I wasn't sure if the furnace board would draw enough current for that relay. I'm assuming that you tested it, right?
 
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Old 12-04-11, 02:13 PM
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Actually I didnt test it before I installed it (I didnt have the board specs...). I has worked fine since it went in...
 
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Old 12-04-11, 03:36 PM
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Yes, that's what I was wondering about. I think those relays were originally designed for contactor loads, but I guess they work fine for resistive loads as well.
 
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