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Experience:  15yrs in the HVAC industry with certificates and degrees.
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Why Does My Lennox Dual-Fuel System with Harmony III Go Into

Customer Question

Why Does My Lennox Dual-Fuel System with Harmony III Go Into 3-Hour Furnace Lock-in?
My Lennox dual-fuel system with a Harmony III zone controller and 4 zones seems to work correctly with the one possible exception that on cold mornings it will often go into the 3-hour furnace lock-in mode after the Balance Point sensor turns off and the heat pump runs for 20 minutes. By the time this happens the outdoor temperature is typically in the low 30’s. The system seems to keep up with heating demand at all times; at least we virtually never see the indoor temperature fall below the temperature setting on any of the thermostats. The house is about 2700 square feet on the main above-grade floor and about 2300 square feet in the basement which is mostly below grade. We live in central Virginia and it seems that the 3-ton heat pump should have no particular trouble providing heat at these temperatures, and I would like to minimize the use of propane.
Indoor unit: EL296UH 070 XV36B-06 (120V, 12.0A, 1/2HP)
Outdoor unit: XP16-036-230-09 (230V, 1/4HP)
Zoning control: Harmony III
Outdoor Balance Point Sensor set to approximately 24 degrees on and 27 degrees off.
Thermostats: Honeywell TH522OD non-programmable set to 1 Heat/1 Cool conventional
Harmony Settings:
Heating Staging Temp: 90
Cooling Staging Temp: 55
Continuous Air Reduction: 0%
Heating Air Reduction: 0%
SYSTEM Configuration: HP, 2COOL, 2HP (all 3 jumpers set to the left)
E-HEAT Stages: DF
PIAB Settings: Zone 1 set to 70%; Zones 2, 3, & 4 set to 50%
DAS 140 jumper: Off
The indoor unit control board DIP switches all set to factory defaults except 11, 12, & 13. These are set to increase Heating Blower Mode Speed by 24%, although I think these are overridden by the Harmony board. A Pressure Switch is connected to the Harmony board but I have never seen the LED turn red. My questions are:
1. Is this normal behavior? If not, what might be going wrong.
2. If normal, is there any way to increase the default 20 minute timeout? I would be happy to give the system more time to meet its heating demand if necessary.
3. Is there any way to decrease the 3 hour lock-in period? It seems unnecessarily long.
Thanks for any advice you can give.
Submitted: 1 year ago.
Category: HVAC
Expert:  BillyHvac replied 1 year ago.

I am very sorry your question has not been picked up yet.

I just logged on and found you had not been assisted.

Please let me know if you still need help and I will do my best. Please do not "Rate" as we have not worked toward an answer yet.

If you would like to proceed let me know by replying. Once again use reply..not "rate".

Customer: replied 1 year ago.
I would like to see your answer. Thanks in advance.
Expert:  BillyHvac replied 1 year ago.


We have 2 different circuits here. One operates the board and thermostats with zones. The other operates the furnace. We will need to know what the led lights in the furnace do when unit is in lockout.

Also you can bypass lockout by turning off/on at furnace for a reboot.

Customer: replied 1 year ago.
During the lockout period, the furnace control board displays the normal sequence as for any other time it's running on propane ("H1" or "H2" followed by "Axxxx" where xxxx is the blower output in cfm). The Harmony III board's diagnostic LEDs show a flashing "0111" display just as the manual says it should. Sometimes there is also a stored "0101" (Insufficient heating) and/or "1010" (DAS detects high heating temp) error code. I assume the 0101 code is generated when the system goes into lockout mode, but I don't know this for sure.Yes, I know that rebooting the system will bypass the lockout mode. I would like to reduce the likelihood of the system going into lockout mode in the first place.
Expert:  BillyHvac replied 1 year ago.

Thank you.

Is air flow ok?

Filter clean?

Barometric bypass working?

Filter is not high efficiency restrictive?

If the das is coding you are running on limit....which is too little air flow for the amount of heat being generated

Customer: replied 1 year ago.
1. I've been keeping a close eye on the filter and changing it as needed.
2. I don't know what barometric bypass is; there's no mention of such in the manuals.
3. I suspect that if there is any actual problem with my system that it has to do with airflow. My blower tops out at about 1250 cfm. See the PIAB settings for the 4 zones that I listed in my original posting. Perhaps these should be increased.
Expert:  BillyHvac replied 1 year ago.

The issue is when only 1 or 2 zones are calling.

We have a furnace that is made to put out "X" btu's.

But then we zone it and say we only want to heat one zone....but the furnace still makes X btus.

If all zones are open we have a normally operating system. But when zones open and close it chokes the system down.....this is where a bypass comes connects the return to the supply.....if one zone calls..the extra air/heat circulates back through the supply to return and creates a loop. This is fine for air flow...but we still have X btu's circling through.

If you can post a pic of the furnace and close duct I will see if/what type bypass yo have. If you didnt have one the furnace life is drastically reduced....

Customer: replied 1 year ago.
The question is not with the furnace but with the heat pump; that is, why it sometimes can't meet demand within 20 minutes and the system goes into heat pump lockout mode. Note that the blower is variable speed and the Harmony board adjusts the airflow depending on the zones that are being fed. Therefore there should theoretically be no need for a bypass (assuming the zone-specific airflows are configured reasonably). There certainly isn't one in my system.I'm not concerned about the occasional "DAS detects high heat" code because this probably only occurs with the furnace running (the high heat limit is 165 degrees) and in any case the Harmony board just shuts off the furnace or heat pump until the temperature drops below a certain temperature.
Expert:  BillyHvac replied 1 year ago.

a high das...That is the number one thing we dont want to happen, whether you can live with it not. This means the furnace/heat pump is peaking to a safety shut down. Not a standard operation, but a safety.

I am speaking from an operational/safety mode and not convenience/inconvenience.

The el296 has a 2 speed (variable) motor...this does not mean it speeds up and down based on restriction or desired cfm. It has low speed for first stage heat and switches to high speed for second stage. You can choose these via dip switches..but it is not a true variable in that reacts constantly and simply targets the 2 different levels of cfm chosen.

I am going to opt out and see if someone can assist you more efficiently.

I wish you the best.

Expert:  HVAC Guru replied 1 year ago.

We are on the honor system for our time, all I ask is please rate my service using the STAR RATING SYSTEM on your page before you leave. If you are not happy with the service please let me know before leaving a negative rating. This is the only way I am paid or credited through the site for my time. This will also allow you to get directly back to me for FREE follow up questions and tips are greatly appreciated! Thanks

Customer: replied 1 year ago.
Billy: OK, thanks for your time. I'm not sure what to do about the rating process, since I have no complaints and I appreciate your efforts but we didn't arrive at an answer. I'll contact Customer Support and discuss the situation with them.

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