heat-pump-defrost-issues

[grege]

Hi,

Had a new lennox xp14 heat pump installed and have a few issues since new (installed 2018):
1. even in warmer weather (ambient temperatures from 65 -70F), the system kicks into defrost mode. WTH? That can't be normal. Defrost board fault identified and replaced several months ago when system was defrosting at 55F. Now defrosts as well around 70F
2. again in warmer weather, outdoor compressor drips a lot of condensation (even at 60-65 degrees) - maybe that's normal for some newer units, but seems excessive.
3. colder weather, defrost mode is associated with a disturbingly loud elephant-like trumpeting noise. Mixing valve? But still, this level of noise cannot be normal.

Any guidance is welcome.
Thanks!
Greg

[pecmsg]

Why are you running it in heat mode at 70°F?

[ksefan]

The defrost sensor should have replaced with the board. Sounds like you might not have needed a new board.

[buford]

Some boards do a defrost on accumulated time even though the defrost sw has not initiated it. Kinda of a fail safe defrost.

[rundawg]

Any guidance is welcome.
Thanks!

Have the installation company verify the refrigerant charge, and the functionality of the two sensors that control the defrost cycle.

Should one of these sensors fail, the unit will defrost every 34 mins of compressor run time when the coil reaches the specified temp.

This units should shut the compressor down for 30 seconds during the switch to defrost, and then back to heating. This is what eliminates the "Moose Call" noise you are hearing. Have you tech verify that too.

[grege]

Why are you running it in heat mode at 70°F?

House is shaded with thermostat set to 68F (63F at night), so the interior house stays cooler than ambient until the afternoon when the system kicks in and starts defrosting.

Greg

[martyinlincoln]

The demand defrost board will go into defrost every 6 hours,even in mild weather, for oil return. Could be sensor problems or running as designed depending on how often it shifts over.
Moose call shifts are usually hot gas too hot and softens plastic in reversing valve. Tech needs to check refrigerant charge and temperature of compressor discharge line.

[grege]

The demand defrost board will go into defrost every 6 hours,even in mild weather, for oil return. Could be sensor problems or running as designed depending on how often it shifts over.
Moose call shifts are usually hot gas too hot and softens plastic in reversing valve. Tech needs to check refrigerant charge and temperature of compressor discharge line.

Oddly, when I first encountered this ealier this year, defrost was kicking in above 50F. My HVAC company's supervisor said it was normal as it related to programmed defrost cycles. An experienced technician I mentioned this to said, no, it isn't normal and only then found a defrost board fault. Since that was replaced, I just recently found the defrost cycle kick in above 65F which makes me think if 50-55F defrost was abnornal, then 65-70F is also abnormal. Refrigerant charge was reportedly normal, so...??? IDK. This, plus the moose calling leaves me completely unimpressed by lennox thus far.

Greg

[grege]

Technician checked it out and all pressures and specs are "normal". Replaced a pitted capacitor (just under 2 years old).

Other: Because the system would cycle on and off too much with the factory 1F temperature differential, I changed it to a 1.5F degree differential and when the house T-stat is set to 68F, auxiliary heat will kick in when the t-stat reads 67F, which suprises me because it will do this even when it's 40F outside.

Whole system uses an icomfort wifi lennox thermostat with lennox's CBX32-MV signature air handler. Not impressed with lennox if this system is "working per spec". It's been louder, less efficient, and far less reliable than the trane xl13i it replaced.

Greg

[BaldLoonie]

Time/temperature defrost control is furnished as
standard equipment.
Control initiates a defrost cycle every 30, 60 or 90
minutes of compressor “on” time at outdoor coil
temperatures below 42°F. Factory setting is 90 minutes.
Anti-short cycle, timed-off control (5 minutes).
Compressor delay (30 seconds, field selectable) for
cycling the compressor in and out of the defrost mode.
High and low pressure switch monitoring with five-trip
lockout.
Two diagnostic LEDs furnished as an aid in
troubleshooting.
Conveniently located in control box.
Anti-short cycle (5 minutes) incorporated into the board.
Diagnostic LEDs furnished as an aid in troubleshooting.

Only thing I see is the temp at which the defrost stat closes is 42° which seems high compared to most. But even if it is running in heat at 60 ambient, the outdoor coil shouldn't hit 42. Need to be sure it is on 90 minutes but still if the defrost stat is not stuck closed, shouldn't be defrosting.

[pecmsg]

GH

Technician checked it out and all pressures and specs are "normal". Replaced a pitted capacitor (just under 2 years old).

Other: Because the system would cycle on and off too much with the factory 1F temperature differential, I changed it to a 1.5F degree differential and when the house T-stat is set to 68F, auxiliary heat will kick in when the t-stat reads 67F, which suprises me because it will do this even when it's 40F outside.

Whole system uses an icomfort wifi lennox thermostat with lennox's CBX32-MV signature air handler. Not impressed with lennox if this system is "working per spec". It's been louder, less efficient, and far less reliable than the trane xl13i it replaced.

Greg

I love “Normal” pressure readings.............some day I may see them!

[beenthere]

The demand defrost board will go into defrost every 6 hours,even in mild weather, for oil return. Could be sensor problems or running as designed depending on how often it shifts over.
Moose call shifts are usually hot gas too hot and softens plastic in reversing valve. Tech needs to check refrigerant charge and temperature of compressor discharge line.

Not at outdoor Temps above 55°F.

[grege]

Between 55 and 60F today and sure enough, defrost kicked in again while I was home after work. A few minutes ago, I grabbed a temperature probe to measure the Y trunk interior duct temperature (just above and within one foot of the main blower cabinet-wyed trunk intersection) as well as the return duct next to the blower unit. The wye trunk supply heat measured 89F while the return measured 69F (holding the probe within each trunk for two minutes after the system was running for a few minutes already). House thermostat is set to 67/68F.

55F outside: isn't 89/90F supply temp that close to the blower pretty weak/low?

Thanks,
Greg

[beenthere]

Yeah, thats low for 55 outside temp.

[grege]

Quick revisit of Earlier response from hvac company supervisor regarding Defrost kicking in on during warmer days-
question: Even when 55F outside, the defrost mode will kick in - is that unusual at such warm ambient air temperatures?

Reply was:
"This is normal. Defrost can be triggered by 2 variables. The primary trigger is a coil temp sensor, when the coil sensor reads cold enough it will trigger. The secondary trigger is a timer. The timer can be set for 30/60/90 mins. If system has operated without a temp trigger for the set amount of minutes then the system will run a proactive defrost cycle just to be sure."

Even when it's 55, 60, or 65F outside??? Replaced defrost board did not change defrosting "abnormality".
Doensn't "demand defrost" 'know/do better' ??? Or is defrosting at 55, 60, or 65F sometimes "normal"???

Asking again for any more clarification because I'm about to send off a nasty-gram to the company to repair or replace. Tired of hearing something is "normal" when it obviously is not.

Thanks for your input as always!
Greg

[beenthere]

Time and temp defrost works by using a temp sensor/thermostat. When the coil temp is below usually 32°F(some lower). A timer runs whenever the compressor runs, and when the run time accumulates to the set amount of time, the board goes into defrost. The timer is reset once a defrost has occurred. It also resets if the coil temp rises above 32 degrees, or whatever its set temp is.

On demand defrost. Uses the outdoor air temp and coil temp to determine if a defrost is needed. When the coil temp drops more than X degrees below outdoor temp(different by manufacture and model) it knows the coil isn't transferring heat as well as it should. And goes into defrost.

It will also go into defrost once every 6 hours of compressor run time, when below X temp, and no other defrost have occurred. This is to protect the compressor from poor oil return if the outdoor coil were to become oil logged.

On demand generally won't go into any defrost above 55°F outdoor temp. 1, the coil won't be iced of frosted up. 2, the outdoor coil won't become oil logged due to the higher refrigerant velocity when its that warm outside.

As I recall. Lennox had a problem with their temp sensors or harnesses. So at one point, if you order a board due to defrost issues, they recommended that you order the defrost kit. Which included the board, and new temp sensors.

[beenthere]

From Lennox manual.

1.Frost Detection  If the compressor runs longer than30 minutes and the actual difference between the clear coil and frosted coil temperatures exceeds the maximum difference allowed by the demand defrost control, a defrost cycle will be initiated.

2.Time  If six hours of heating mode compressor run time has elapsed since the last defrost cycle while the coil temperature remains below 35°F (2°C), the demand defrost control will initiate a defrost cycle.

[rundawg]

Reply was:
"This is normal. Defrost can be triggered by 2 variables. The primary trigger is a coil temp sensor, when the coil sensor reads cold enough it will trigger. The secondary trigger is a timer. The timer can be set for 30/60/90 mins. If system has operated without a temp trigger for the set amount of minutes then the system will run a proactive defrost cycle just to be sure."

Do you have the full model number of this unit?

These Lennox XP14 series came in both "Demand Defrost" (revision -01 thru -07) and Time-Temp Defrost" (revision -08 and Later).

From what you are describing, it sounds like you have the "Time-Temp" version, which doesn't have the 6 hour defrost cycle if no defrost has occurred (as "beenthere" mentioned- only demand defrost units).

The defrost thermostat on these 'Time-Temp" units, does close at 42ºf (coil temp, not outside air temp), and start the defrost timings (30-60-90).

Sounds like your HVAC guy is telling you the features of both types of controls, so it would be nice to know the exact mode number you have.

Sidenote: you stated the defrost control has been changed, so it might have been change to a different type control than the original. The number on the defrost control board should solve that confusion.

[grege]

Thanks All !

I will look for a specific model number and post that. Since it was a new 2018 install, I expect it's the time-temp defrost.

Greg

[grege]

Just took plenum temperatures and will continue to track those over the next week.
45F outside. Wye plenum supply temperature just above blower 85F while return plenum temperature is 66F.

blower model #:
M/N CB32MXV-036-230-06
S/N 1617H 23978

exterior compressor model #
M/N XP14-036-230-10
S/N 5817H 15483

Greg