This System was Setup to Fail! HVAC Tech Saves 15-$20K Trane Variable Speed System On Maintenance

I made this video to show the importance of doing thorough maintenance, whether the system is new or old. I ran across this Trane XV variable speed system that was set up to fail from the start. It ran with 700 CFM of airflow on a 4 ton system for about a year due to improper setup in commissioning. The installers forgot to connect the BK terminal and cut the BK jumper for Variable and Airflow signal to the board.

[@iseeyou9078]

Yep i see the fan speed not set up correctly alot on 2 stage and variable speed . Also people still just going off pressures instead of checking subcooling and superheat. If you hook up your gauges then check sh and sc. The same old saying ive been doing it like this for 5, 10 years. Good Job

[@HVACTechKnowledgy]

Thanks a lot! Appreciate the feedback.

[@adamcraig1568]

So many units and so much to learn lol don’t see many Trane units like that one in the video in my area (West of Charlotte).

[@danpmatz]

You can set up the cfm per ton on the board. It ask what size outdoor unit Then how many cfm you want in cooling and heating

[@Bennys-Life]

Looks like the evap coil close to freezing

[@97Napkins]

Was thinking maybe coil inside partially frozen

[@BenHC]

Recently found a similar install issue with my furnace in the house I just bought. Not the weird common wiring, but the lack of wiring BK, mine didn't have the jumper cut. I noticed it when trying to test out the various fan settings and noticing that it only seemed to work at one speed. This sent me down the path of reading the manuals and contacting the original installer (no longer does HVAC) and eventually getting a new tech on the phone who confirmed my suspicions and said he could fix it for $200 or I could do it myself. I found your video when looking for confirmation of my plan and it gave me the confidence to do it myself. My fan speed now clearly is different at 50/75/100%. Any idea of what percentage it defaults to if bk isn't wired? It feels like 100% is a lot higher than it used to run and I'm curious how much fan performance I've gained lol.

[@ddcws1]

I set up an S9V furnace with a Honeywell 8321 stat. Jumped R/U1 and connected other U1 to BK at board and cut jumper. Programmed thermostat to dehumidify with equipment in A/C with low fan and set contacts a normally closed. It was definitely running lower cfm but showed it was also running 2nd stg as well. Honeywell instructions stated dehum would run if 2nd stg was calling. So a little confused. Does the logic on board override that or did I not program it properly?

[@nathanhurst5155]

I work primarily on trane as well and quite often find suction line temp higher than I would like to see as well slightly higher superheat. On those coils they have a sticker in regards to that as well. It says something like when measuring outside ar the condenser the superheat may measure 15-25 degrees. So it must be normal even tho I don’t like it, it is what it is. Depending on line length it can measure better with a real short lineset.

[@allanbrito13]

Too much airflow causes a higher suction pressure

[@HVACTechKnowledgy]

True but the suction pressure wasn't High it was actually suction line temperature that was slightly high pressure was actually a tad low.

[@jeremiahmiller7796]

Was that a txv or exv? If it was a txv you should be able to adjust for proper superheat. With the exv systems sometimes it’s as simple as thermistor that reads a bit off.

[@HVACTechKnowledgy]

Oh yeah thanks I didn't even think of that. It was definitely at the TXV

[@pubchat2913]

Nice vid man. What was outdoor and indoor temp? I was surprised at that super heat, how long of a line set?

[@HVACTechKnowledgy]

Thanks! The outdoor was 75 And the indoor was 71. Yeah the Superheat threw me off as well. The line set couldn't have been anymore than 60 ft or so...

[@pubchat2913]

@@HVACTechKnowledgy 60 feet is still a lot I’d say. Around here we typically don’t see anything over 30 feet, 20 is the average.

[@roberts1159]

So seeing the low airflow on the air handler board was what clued you in there was an issue? Thanks for sharing

[@HVACTechKnowledgy]

Yeah that and the 37 degree delta T.

[@HVACGUY]

What relay panel is that?

[@HVACTechKnowledgy]

Its the BAY24VRPAC52DB

[@abnergarcia6252]

So what does the BK terminal do? Cutting or not cutting the jumper?

[@HVACTechKnowledgy]

The bk terminal supplies a pwm(pulse with modulation) to the control board for fan speed control.

[@worlddemize]

all this time I thought that bk was fer BURGER KING

[@HVACTechKnowledgy]

lol

[@realSamAndrew]

At 11:17 what is return dp and supply dp?

[@HVACTechKnowledgy]

41 degree supply 45 degree return dp

[@realSamAndrew]

@@HVACTechKnowledgy what is dp? I.E what does it mean?

[@HVACTechKnowledgy]

Dew point. Its the temperature that the water vapor in the air condenses...

[@realSamAndrew]

@@HVACTechKnowledgy d'oh! Brain freeze. Thanks!

[@biblebloopers946]

So what exactly is BK?

[@HVACTechKnowledgy]

BK is a feature used on systems with variable speed blowers to either reduce the speed by a certain percentage, by cutting 24volts or sending a PWM signal to vary the fan speed based off load demand on communicating variable refrigerant system.

[@biblebloopers946]

@@HVACTechKnowledgy what's the chances of getting you to make a video explaining this in detail?

[@HVACTechKnowledgy]

Chances are pretty good, I was actually already planning on it : ) Im just waiting to come across a zoned variable speed system with a honeywell zone board to demonstrate how to use bk to slow down fan speed when only a single zone is calling. Thanks!

[@biblebloopers946]

@@HVACTechKnowledgy i look forward to it

[@elijahgoodman3140]

So do I. Good job

[@kenedward4585]

Can you tell me what these TAM7 + XR14 lights mean: kzbin.info/www/bejne/m6a9qahnYtaWp80

[@HVACTechKnowledgy]

If I'm not mistaken the top board is the air flow control board the green LED flash is 12 times which indicates 1200 CFM the blue led flashes once which indicates normal operation and the red flashes 11 time which indicates there's a evc fault The lower board is the EVC board (electronic valve control) Five green flashes indicate first stage Heating the single blue LED flashes normal operation and the Seven red flashes indicate high superheat. Could be a low on charge or restricted metering device.

[@kenedward4585]

@@HVACTechKnowledgy turns out the coil was replaced and the tech forgot to reset the fault.