Getting complaints from teachers about humidity and unable to reach thermostat set point. Brand new units installed by…

Had one of the install/commissioning techs tell me that “you charge the old 410a systems by sub cool, but 454b is charged by line set. 454b is different because it’s mostly gas.” At which point I restrained myself and kept it as professional as possible while pushing back on such a wild statement.

Have you confirmed your airflow. Any Test and balance been performed yet or planned to be performed.

Not on my end. Needing to add to the tool bag soon. I’ll have to get specifics from the contractor the next time we meet, as to what’s been done. As of now, their manager has gotten involved and reaching out to Lennox to verify how the unit is to be charged which leaves me doubting everything they’ve done Forgive this question, as I’m newer to this, but can airflow be so bad that it creates a 10 degree false read (ie reading 4 when it may be properly charged to 14)?

UPDATE: I was reading that Lennox includes a factory jumper from R to Ds on the RDS board. Without that jumper and not running a “D” wire from thermostat to board, the system will always run at dehumidification speed. It appears they removed that jumper and never wired in the thermostat correctly. That might explain why I noticed the systems running low speed all the time, despite thermostat reading 4-5 degrees away from set point? Coupled with severe undercharge, might be the issue? Just spit-ballin

Great job finding the jumper! Yes put that jumper back on. You should find your pressures a bit different now with higher airflow. Your total enthalpy will tell the tale. I’m not sure how to get that value from MQ. (Delta 7 btu/lb) I know it’s pretty easy on the Field piece job link app. You have to input the airflow value to get that reading though. Can you try that?

Thanks. Yes, MQ has enthalpy (delta btu/lb). At the moment, my employer has me tasked out with other duties so I wasn't able to address the jumper yesterday. I did address another setting at the condensing unit. Adjusted the "operation mode" pin from "efficiency" to "comfort". That ramped up the compressor and fan motor, moving suction sat from 56 to 45 degrees. Enthalpy from 2.41 to 5.46. Indoor temp split from 8.5 to 14.1. If I had been able to put that jumper back in at RDS board, I think we would've seen further improvement with the increased air flow, but I was pulled off. Subcool measuresd only 3.2 so I'm still thinking undercharged, as well. For context, I work for a school (facility maintenance) and we are undergoing a large new construction project. Multiple new buildings. Of course, the builder subbed out this HVAC company and now I'm told a Lennox rep is coming out next week. Looking forward to that meeting.

Lennox rep (sales) came out with an independent tech whom he subs out. The R to Ds jumper is in. Apparently the installation company didn’t run Y2, Only Y1. The new tech hooked up Y2 at the air handler control board, thermostat (Lennox cs7500) and condenser. Condenser wasn’t getting the Y2 call even though thermostat was calling for 5 degrees cooler than current room temp. He had to go to another job so decided to jump out Y1-Y2 so the unit runs second stage all the time. The result has been much better cooling and dehumidification. I also measured 7-8 degrees subcool vs the previous 3-4 degrees. Likely due to higher stage. Still not close to the target 14 degrees that the manual calls for. However, the liquid line is no longer “pulsing” at the air handler when you grab it. Of course everyone inside is happy but we will need to figure out why stat isn’t getting Y2 call to the unit. I haven’t had much time to go assess but plan to soon.