[cpncrunch]

We got a new heat pump a couple of years ago, and ever since we go it it has been doing this. What happens is that if the coil temperature is just above freezing (so it doesn't auto defrost), and then the ambient temperature warms up, the frost at the top of the coil never clears.

Today, for example, OAT was around 32F this morning (so no auto defrost), and then it warmed up but there is still frost on the top quarter of the coil, and on various pipes:

OAT sensor=50F (has been this temp for 3+ hours)
coil sensor=50F
indoor temp=71F
heat register temp=86F

Then, I decided to manually defrost for 5 mins which completely removed the frost from the fins, coils and pipes. Afterwards:

OAT sensor=50F
coil sensor=48F
indoor temp=71F
heat register temp=93F

I'm just unsure if this is normal, as it seems a bit odd that the top of the coil should be frosted up at 50F (so presumably the top of the coil is <32F), yet the coil sensor is showing 50F. Is there that big a temperature difference over the coil? I wouldn't have thought so, as none of the coil is normally frosted up at this temp.

The problem is that when the temp stays just above 32F the top half of the coil remains frosted up and reduces the efficiency by 50%, even after the temperature warms up. When it warms up the coil partially defrosts, but the top quarter always remains frosted up unless you manually defrost, or the heat is off for a few hours.

Installer has serviced it about 4 times since, and each time temps and pressures are 100% perfect (but it's never been frosted up). They say that this model (GSZC160241CA) has a big coil and can handle a bit of frost. That is true, but the issue is that I have to manually defrost when it's been cold in the morning otherwise it takes twice as long to heat the house up, and I'm wondering if there is some issue with it or if this is normal.

This model has a duct around the fan to supposedly increase efficiency, but I'm wondering if the fan duct reduces airflow to the top quarter of the coil and that's what is causing the problem.

Auto defrost is working 100% perfectly. The problem is only when the coil temperature is just above 32F and then warms up. It would be nice if I was able to adjust the defrost temp via comfortnet, but they don't have that feature.

 

[Juan Madera]

Had one Ruud, new out of the box, frosted several coils in the middle that did not defrost. Turned out to be a restriction in that circuit from the factory. H/O got a new one on warranty and I installed at no cost to H/O....

Might wanna mention this to your contractor.

 

[cpncrunch]

Had one Ruud, new out of the box, frosted several coils in the middle that did not defrost. Turned out to be a restriction in that circuit from the factory. H/O got a new one on warranty and I installed at no cost to H/O....

Might wanna mention this to your contractor.

With mine all coils defrost properly when the heat pump is in defrost/cooling mode. It's just that the top remains frosted up after the ambient temperature rises a lot, and the frost just stays there, dropping the heat output by a third to a half.

 

[Bazooka Joe]

“Installer has serviced it about 4 times since, and each time temps and pressures are 100% perfect.”

What does that mean? How did they charge your system initially and when did they initially install your system? In the winter or cooler temperatures, below 60 degree.

There is a very specific way Goodman wants their 2 stage system charged initially, system needs to run for 10+ minutes first, check/charge in cool mode with OD temperature above 60 degree and charge in 1st stage. Certainly need to set CFM , have matched systems helps. What is the model number of your indoor unit. If it’s a AR*F they are suppose to remove the piston metering device and install a OEM external mounted ( next to the Air Handler ) TXV to get the matched AHRI system. You got photos of the indoor section.

https://cdn.iwae.com/media/manuals/goodman/gszc16-installation.pdf Page 7 discusses the charging procedure.

How did they do the final field refrigerant charge. Did they leave your blower speed to factory default setting or set it to your system? Did they check your static pressures?

Have them call Goodman Technical Rep. with those pictures for feedback. Tech. Rep. does not deal with homeowners. Possibly the charge is off, they can possibly recover charge, blow out in both directions with nitrogen, evacuate, weight in charge ( including for lineset over 15’ ) then weight in virgin refrigerant. When warmer weather comes then check/charge to subcooling/superheat, exactly as the guide says, with one sensor 6”-8” from compressor. If you have a non adjustable TXV at indoor coil, they want system charged to subcooling only.

Here’s the install guide you can read the detailed charging procedure. Guide says you should have a minimum 10” clearance from a wall, yours looks closer than that. Guide recommends elevating unit 2 1/2” off ground if in area above +15 degree.

From the photo of the insides, it looks like there are several smaller thin bands ( 3rd picture ) of frost further down from the top also. Possibly a charge issue or OD metering device issue. Seems like it’s icing at the TXV ( 2nd picture ) and everything downstream ( heat mode ) of that value has frost on it going into the coil? The drier ( black canister in 2nd photo ) looks OK as no sweating or frost accumulation on it ( no partial restriction ) Errr if seeing and identifing everything correctly.....

Right or wrong my :.02: worth..

 

[cpncrunch]

The indoor unit is AVPTC25B14 and is matched to the outdoor unit. Same installer installed it a year prior to the new outdoor unit. I don't have all the info about how exactly they installed it, but they measure the pressures twice a year and it is exactly as per their charts. Does that mean the charge is correct?

Yes, it does look to me that it is frosting up below the TXV. But after I defrost it there is no frost there.

I think there is at least 10in of clearance from the wall. It just looks less in that pic due to where I took it from. No problem with airflow, except to the top of the coil (where it's frosting), due to the duct around the fan.

My problem is that I don't know if there is in fact a problem with this unit or if this is the normal way it operates.

 

[Bazooka Joe]

The AVPTC has a factory TXV, the T stands for TXV, don’t know if that Air Handler TXV is adjustable, as the install guide says to charge to subcooling in 1st stage in cool mode ( above 60 degree OD temperature ) if the metering device is non adjustable.

Yes putting it in defrost, reverse refrigerant flow and bypasses the outdoor metering device ( internally ) to melt the ice. But the OD metering device is functioning in heat mode.

Thinking maybe ride it out until warmer weather ( 70+ degree OD temperature , 70-80 degree indoor temperatures) let system run 15+ minutes then check/adjust while in 1st stage cooling. If your Air Handler has a non adjustable TXV check/charge to subcooling, providing CFM was set correctly, if the Air Handler has a adjustable metering device check/charge to subcooling/superheat as instructions says....what wrong with following the manufacturers install guide?

I would consider dropping this company and find a competent Tech. who is well versed in Goodman Heat Pump set up procedure. Then take it from there. Should not cost you more than 1-2 hours labor plus trip charge plus labor tax.

BTW your system is a AHRI matched system. Doesn’t quite give you 16 SEER thou, it’s 15 SEER, 8.5 HSPF, and 12.5 EER AHRI number 202541735 those numbers are not real world but you get a idea of the ratings.

To check certificate https://www.google.com/url?sa=t&rct...jALegQIQRAD&url=https://www.ahridirectory.org/&usg=AOvVaw1Psb39iTznxCFNAi8fJHHj

I hope you registered your system as Goodman gives a outstanding manufacturers warranty, if you failed to register your system initially chances your manufacturers warranty dropped significantly.

California and Quebec need not register system to receive maximum manufacturers warranty.

Do you live in a snow belt state, as that OD unit should be elevated off the ground for better water drainage during defrost.

 

[cpncrunch]

Yes, our system is all registered for the warranty. The install company is very competent and experienced with Goodman. We spent a long time going through the incompetent companies before spending a large amount of cash to install the system with this company. They have very experienced techs who know what they're doing. AFAIK they did follow the installer instructions properly, and they measure subcooling/superheat, etc every summer and it is all perfect. I'm just a homeowner, I don't have the ability to do any servicing myself. I can certainly pay them to look at it, but right now I'm uncertain if there is actually a problem. We don't get much snow here, and the heat pump is pretty well protected from snow due to the house on one side and trees on the other, so that's never been an issue.

Just looking for some steps to go from here.

 

[Bazooka Joe]

To me there is no reason to check subcooling/superheat every summer, if the charge was done correctly from initial install and system is working properly, and no complaints. One Tech. checking those numbers can be completely different from another Tech. numbers. What the purpose of checking if it’s working great?

Thinking they are checking subcooling/superheat ( again if the Air Handler has a non adjustable TXV at indoor unit any adjustment is to subcooling only as install guide says ) more for trying to figure it out instead of a PM check, as I’m sure your telling them about the icing issue, but they are not telling you that?

They may have experienced Tech. but Heat Pumps are another animal compared to straight cooling, who to say they have a lot of experience in this particular model Heat Pump. It’s not like you have a bare bone 13/14 SEER Uncomplicated single stage Heat Pump. Your system is not as complicated as a variable speed system, but more complicated than a bare bone unit.

“Just looking for some steps to go from here”

So again from me anyway in regards to your last statement in your last post that’s my :.02: worth.

“That is true, but the issue is that I have to manually defrost when it's been cold in the morning otherwise it takes twice as long to heat the house up, and I'm wondering if there is some issue with it or if this is normal.”


I would at the very least have them upchannel those pictures to Tech. Rep. and query them, course they may say all is OK when it’s not. It’s not like they are going to tell you that they made a mistake. Possibly there is a Technical Order ( TO ) as an example to move defrost sensors to a different location or what not? Proving refrigerant charge is dead on. Why would the system be OK if you say you have to manually defrost it??? To me that is not correct, thinking you have issues. IMO These guys don’t have the answer.



What does this mean?? What fan are you referencing?

This model has a duct around the fan to supposedly increase efficiency, but I'm wondering if the fan duct reduces airflow to the top quarter of the coil and that's what is causing the problem.

 

[cpncrunch]

They service the heat pump twice a year, and check the various temps and pressures (not sure exactly which) during that service. May or may not be necessary for a unit working properly, but for now I'm paying for that service.

The fan I'm talking about is the fan in the outdoor unit. It has a plastic or rubber duct/sheath around the fan, which you can see in the third pic. Our last heat pump didn't have this. I'm just suspicious of it, as the part that tends to stay frosted is the bit under the duct, where there is reduced airflow due to the duct.

I only have to manually defrost it to improve the efficiency, but it isn't strictly necessary, so I'm just wondering if this is normal or if I'm expecting too much, or if it's a design flaw or whatever. If the coil sensor was on the coldest part of the coil it wouldn't be an issue as it would just defrost the entire coil rather than leaving the top quarter frosted. But the sensor isn't on the coldest part of the coil, so again that might be a design issue. Right now I don't have enough info to know if this is an actual problem that can be fixed.

 

[Bazooka Joe]

You can get 4 or 5 different Techs. with different experience/skill levels and ask each of them to give you the subcooling and superheat number of your system and you could easily get several different numbers from each of them.

How experienced can they be, they couldn’t even place the unit 10” minimum from a wall ( at least from that view it does not look like the minimum 10” certainly could be wrong ) and elevate the unit off the ground like the guide mentions? Is your Air Handler in a attic? If so did they install the inverted trap that says your suppose to install on attic Air Handlers? Page 4 of the guide..

50 degree OD temperature and your only getting 15 degree split in your 1st post 1st line, then next line 22 degree split on 2nd line, heck my two 16 year old Heat Pump can easily reach high 20 to 30+ degree split ( return to supply register) at 50 degree OD temperatures. Even my attic unit ( in cold attic ) does better than those numbers. Basement Air Handler does well. Those numbers are nothing to write home about IMO....

What’s your defrost time set at? 30/60/90/120 says those time intervals numbers in the guide

 

[cpncrunch]

They use a digital gauge which shows both subcooling and superheat, so I don't think it's possible to measure it wrong unless you put the clamps in the wrong place. But I'm not an HVAC engineer, so I could be wrong.

I just measured the clearance, and the outdoor unit is 9-10 in from the siding. Indoor unit is in basement. Defrost time is set to 60 (which I can change). But that's not the problem. It works 100% when it defrosts automatically. The problem is only when coil temp is above 32F, which means auto defrost doesn't happen (as it is fixed at 32F and can't be changed).

The 22F split was for the clean coil, 15F was when it was partially frosted. But I was just comparing to thermostat temp rather than return inlet...I see it's 3 degrees colder, so 25F is more accurate. I'm getting similar readings at 41F OAT.

 

[Bazooka Joe]

The 32 degree defrost sensor, ( who told you it’s 32 degree, ) and not 27 degree as an example? It’s not like it’s stamped on the electrical data plate? Did not initially see it listed on the install guide, the Techs told you?

Did they verify the defrost sensor ( and any other sensors ) is reading the correct coil temperature? If it’s a sensor? and not a snap acting defrost thermostat, which is either open or closed. Still should be able to tell if it closes at 32 degree ( snap acting type ) if put in ice water.

Did they clamp 6”-8” from the compressor, guessing the answer is no as that would entail removing panels to get close to the compressor. Not sure why they want it clamped at that specific location vs further away. It says that in the install guide at that specific location.

“Today, for example, OAT was around 32F this morning (so no auto defrost), and then it warmed up but there is still frost on the top quarter of the coil, and on various pipes.”

Doesn’t the defrost sensor 1st have to close ( after the 60 minute times out, as long as the defrost switch stays closed for that amount of time ) typically that’s what happens on a time/temperature defrost system what is the OAT, is that a sensor on the unit, or is that reading the ambient air and tied to your thermostat?

Anyway doesn’t hurt to call Technical Services, or if the distributor has a trained person ( which I doubt ) Goodman Tech. Service that can actually go to the site with the Contractor to check your system like other manufacturers have. It’s not like Goodman/Daikin is a small company, they are number one or two in residential sales. I would try to get Technical Services on the job if at all possible to check along with the Installing Contractor, to get another set of eyes.

 

[mgenius33]

Poor defrost control design, if this unit still uses the timed defrost. We had a lot of rain this winter with near freezing temperatures. We received quite a few defrost issues with this same design.
The defrost system uses outdated engineering with a bimetal switch. The switch is located on the second row from the bottom, so it never senses the top of the coil. While this isn’t an issue with many of the brands that used to use this old technology, I believe the coil design does not allow for equal refrigerant flow with 410A. This old defrost design seemed to work better on R22. Most brands have gone to “demand defrost” with the newer 410A equipment. Opposed to common belief, not all brands are the same...

 

[cpncrunch]

The 32 degree defrost sensor, ( who told you it’s 32 degree, ) and not 27 degree as an example? It’s not like it’s stamped on the electrical data plate? Did not initially see it listed on the install guide, the Techs told you?

It says that in the service manual, and it is working 100% for the past 2 years: it always defrosts at 31F and never at 32F.

 

[cpncrunch]

Poor defrost control design, if this unit still uses the timed defrost. We had a lot of rain this winter with near freezing temperatures. We received quite a few defrost issues with this same design.
The defrost system uses outdated engineering with a bimetal switch. The switch is located on the second row from the bottom, so it never senses the top of the coil. While this isn’t an issue with many of the brands that used to use this old technology, I believe the coil design does not allow for equal refrigerant flow with 410A. This old defrost design seemed to work better on R22. Most brands have gone to “demand defrost” with the newer 410A equipment. Opposed to common belief, not all brands are the same...

Yeah, that seems to be what's happening. Given that Goodman defrost sensors/boards are hard-wired to only defrost below 32F, what are my options? Get my installer to talk to Goodman and explain that it isn't always defrosting the top of the coil? They say it's working as designed. Or is there scope to move the sensor to a different location near the top of the coil or between the TXV and the coil in the area that frosts up first?

 

[Bazooka Joe]

It says that in the service manual, and it is working 100% for the past 2 years: it always defrosts at 31F and never at 32F.

You realize that the defrost thermostat is attached to a lower tube bend and senses coil temperature not OD temperature? in any way, once it initiates a defrost ( as long as that defrost thermostat stays closed and the board runs 60 minutes does it actually initiate a defrost, then once the defrost thermostat senses the tube temperature that it’s attached to reaches around 75 degree it terminates a defrost. If the defrost thermostat fails to open to take it out of defrost ( after tube temperature reaches 75 degree ) it will run for a total of 10 minutes whereas the defrost board takes it out of defrost under a safety condition. A normal defrost times could be a couple minutes to close to 10, the point is the defrost times varies and is not the same amount every time. I just threw out 75 degree termination, it could easily be a slightly different number. Also those defrost thermostat are not exact, so if it closes at 31 or 33 that’s falls under the acceptable range. Those defrost ( snap acting ones ) are not highly accurate right down to a fraction of a degree. They are just standard cheap controls.

Sounds like you have temperature control monitors hooked to your Outdoor unit Heat Pump, because how would you know it’s 31 degree coil temperature and never 32 degree as you state? ( in the above statement ) unless you and I are not on the same page.

So the techs used electronic equipment to check charge, I call that the dumbing down effect, they probably would be lost if they had to do it using non electronic equipment to get those readings. Reason I mentioned if you had several different Tech. taking readings you may get several I was thinking more old school methods. So my fault on that analogy.

 

[cpncrunch]

You realize that the defrost thermostat is attached to a lower tube bend and senses coil temperature not OD temperature? in any way, once it initiates a defrost ( as long as that defrost thermostat stays closed and the board runs 60 minutes does it actually initiate a defrost, then once the defrost thermostat senses the tube temperature that it’s attached to reaches around 75 degree it terminates a defrost. If the defrost thermostat fails to open to take it out of defrost ( after tube temperature reaches 75 degree ) it will run for a total of 10 minutes whereas the defrost board takes it out of defrost under a safety condition. A normal defrost times could be a couple minutes to close to 10, the point is the defrost times varies and is not the same amount every time. I just threw out 75 degree termination, it could easily be a slightly different number. Also those defrost thermostat are not exact, so if it closes at 31 or 33 that’s falls under the acceptable range. Those defrost ( snap acting ones ) are not highly accurate right down to a fraction of a degree. They are just standard cheap controls.

Yes, I'm aware of all that. Our system has coil and OAT sensors that I can see on the comfornet system (those are standard for this Goodman unit). It cleans the entire coil of frost when coil temp is below 32F, and the coil temp corresponds to the OAT sensor (within 2 degrees). You can see the coil temp increase during the defrost so the sensor is definitely attached to the coil somewhere, and it generally terminates within 5 mins except a few times a year when it reaches the 10 min cut-off and a DT (defrost termination) error is logged to the errorlog. And the defrost is also checked twice a year by the company who service the system. So I'm pretty sure the defrost is all working 100% perfectly.

 

[Bazooka Joe]

Yes, I'm aware of all that. Our system has coil and OAT sensors that I can see on the comfornet system, and I'm certain the defrost is working perfectly. It cleans the entire coil of frost when coil temp is below 32F, and the coil temp corresponds to the OAT sensor (within 2 degrees). You can see the coil temp increase during the defrost so the sensor is definitely attached to the coil somewhere, and it generally terminates within 5 mins except a few times a year when it reaches the 10 min cut-off and a DT (defrost termination) error is logged to the errorlog. And the defrost is also checked twice a year by the company who service the system. So I'm pretty sure the defrost is all working 100% perfectly.

IMO it should never ( defrost board you seem to indicate that it’s doing as your getting a error code, yes? ) take it out of defrost, that’s a safety only protection, last I checked, as you mentioned it doing that, so how can manually defrosting it ( as you say you do and the defrost board taking it out of defrost ( as a safety ) as you seem to indicate due to error codes be considered normal operation ) Hate to sound like a broken record but I would insist on getting Technical Service out with that information details that you mentioned and tell them. Put it in there hands, see what they say. Again Heat Pumps to a degree is its own career field. I was taught decades ago a split system heat pump are critically charged systems, you really need to dial in the charge down to the last ounce for optimal performance, everything needs to fall into place, correctly sized ductwork, static pressures, CFM of equipment, matched systems, correctly sized kink free lineset, etc. etc. it’s not as forgiving as straight A/C units where you can pretty much charge to a beer can cold suction line, lol.

 

[cpncrunch]

IMO it should never ( defrost board you seem to indicate that doing as your getting a error code, yes? ) take it out of defrost, that’s a safety only protection, as you mentioned it doing that, so how can manually defrosting it ( as you say you do and the defrost board taking it out of defrost ( as a safety ) be considered normal operation ) Hate to sound like a broken record but I would insist on getting Technical Service out with that information details that you mentioned and tell them. Again Heat Pumps to a degree is its own career field. I was taught decades ago a split system heat pump are critically charged systems, you really need to dial in the charge down to the last ounce for optimal performance, everything needs to fall into place, correctly sized ductwork, static pressures, CFM of equipment, matched systems, correctly sized kink free lineset, etc. etc. it’s not as forgiving as straight A/C units where you can pretty much charge to a beer can cold suction line, lol.

It only tends to hit the 10 min limit about once a year. That happens when it frosts up quite a lot when temp is hovering around 32F so a lot of frost builds up before it hits the magic 31F temp to start defrosting. I don't think this is anything to worry about, but hey I'm not the expert here.

Yeah, I likely will get them to contact Goodman, but I just want to get all my facts straight before I ask them to do that so I'm not fobbed off by anyone.

 

[Bazooka Joe]

It only tends to hit the 10 min limit about once a year. That happens when it frosts up quite a lot when temp is hovering around 32F so a lot of frost builds up before it hits the magic 31F temp to start defrosting. I don't think this is anything to worry about, but hey I'm not the expert here.

Yeah, I likely will get them to contact Goodman, but I just want to get all my facts straight before I ask them to do that so I'm not fobbed off by anyone.

Thinking I’ll tap out, not much more I can add, others here certainly can fill you in better than me.... If you do find anything wrong, or even if they say, hey continue to put in manual and let the defrost board take it out of defrost once in a blue moon as a safety only, is normal operation, please mention either way here as speaking for myself I’m curious what becomes of your system.