Regular Guest
American standard Platimun ZM20 heat pump running excessively on aux. heat
We just had an American Standard Platinum ZM20 heat pump with a new Platinum ZV air handler installed to replace our aging Trane 24+ year old 13 seer heat pump. The new unit seems to be operating very often on the aux heat strips. I understand that heat pumps will run on the heat strips if there is a 3+ degree difference between the inside temp and the set point, but it runs on aux heat when the set point and indoor temp are the same at the thermostat (set point 68 and inside temp of 68). It doesn't always operate on the heat strips when the set point and temp are the same and it doesn't always operate on the heat strips when there is a temp differential- say set point 70 and indoor temp of 68. It does very often though on both accounts. Several times when I have checked and the aux heat strips were being used I walked away and checked a few minutes later and it was then not operating on aux heat, but still heating with no change to the set point or inside temp. We have the temp differential set for no more than 2 degrees, ie. sleep set at 68, wake set at 70.
Outside temp has been up to the mid 40's during the day and down to around 24 at night. It has been operating on the heat strips throughout the day- even when the outside temp is 40+.
The unit was installed Friday 1-18 with several error codes showing on the thermostat. Another tech came out Saturday and evidently fixed what needed to be fixed and there are now no error codes. It is a communicating system with an outside temp sensor. When I asked my salesman yesterday (Monday) I was told that I should wait a couple weeks to give the unit time to learn. I would like to know if I am being fed a line of BS. It seems to me that if the set point and temp are the same then it should not operate on the aux heat strips- ever!
If anyone could enlighten me on the learning process of the communicating system I would appreciate that too.
My salesman also implied that I could turn down the temp at night more than 2 degrees and it wouldn't be an issue with the heat strips, but it seems to me that the system will run much more on aux heat if I do that- especially since it is running on aux heat with little to no temp differential.
Outdoor Unit: Platinum ZM 20, 4A6Z0036B1000A
Indoor Unit: Platinum ZV AMSTAM8A0C36V31CA
Comfort Control: Yes (AMS) (ACONT900AC43UA)
Heat Strips Yes ABAYEVBC20BK1AA
Air Cleaner: Accuclean AFD235CLAH000C
Regular Guest
Went home for lunch and manually adjusted temp to 70 from 68. System operated in standard heat mode to bring temp up. I checked every 5 minutes to be sure. Towards the end of lunch about 45 minutes in, checked and the system was running on aux heat strips. Thermostat read 70 and 70- set point and inside temp. Outside temp was 39 degrees according to the thermostat.
Professional Member*
Do you know what the outside stat is set at? Is the outside unit in defrost mode when the stat shows heat strips are on?
Blue Fox
Regular Guest
I do not know what the outside stat is set at. I had considered that it may be in defrost mode. I'm not sure it needs to defrost that often, but being a smart, learning thermostat it is possible.
I went out of town Wednesday through Friday and when we got home Friday night we had new error codes showing (not the same as when it was first hooked up) and no heat. The tech came out and basically reset the system. It ran for a while but when we woke in the morning the same error codes were showing and no heat again. A different tech came out and found that two of the coil sensor wires were hooked up wrong. He thought that may have caused the excessive heat strip operation since the high and low pressure sensors were hooked up backwards. We hoped that was the issue and we would run trouble free from here on out, but 7 hours later the heat pump displayed the same codes again and no heat. This time it was 7:00pm on Saturday night so I just reset the heat pump (by turning the breaker off then on) at 10:30 before we went to bed. It is now 10:00am and the heat pump is still operating with no error codes yet. The error codes that it was displaying are 89 and 91- missing component and communication error.
Does anyone have an idea what is going on with my unit? Do I have a bad thermostat? Why would you just be able to turn the power off to the unit and turn it back on and have it run for 7-12 hours before a communication error occurred. Shouldn't it have a error right away if it can't communicate with a component of the system? Any other suggestions for troubleshooting?
Professional Member*
What t-stat do you have? There was a problem with Trane/American standard comm. air handlers paired with XL20 or ZM20 heat pumps. These was with the new 9500 series t-stat. I don't think it was for the 900 t-stat though. To tell the Diffrance the 9500 t-stat is in color with a lot more options compaired to the 900 t-stat that just has a green display. Both are comm. stats. Due to this problem we have only used the 900 stat on XL20 and comm. Hyperion air handlers.
I would ask the dealer to contact local support tech to come out to the home with them to trouble shoot the problem as it has been on going for quiet some time and I Am sure you are a little upset. Sometimes it just takes another set of eyes on the problem to correct it. Please keep us posted.
Regular Guest
I believe it is the 900 series T-stat. I was considering upgrading to the 9500 though. Has anyone else had problems with the 9500 and the ZM20? I assumed that it would be a better t-stat to pair with the unit since it does have more options and reporting. Should I stick with the 900, go to the 9500, or should I look at other options?
I have not had any error codes since I reset the heat pump Saturday night at 10:30pm- about a day and a half ago. I will be contacting my dealer and requesting a local support tech come out to help trouble shoot anyhow. I would think there has to be some issue if it shut down after 7 hours and all I did to "fix" it was turn the breaker off, wait a couple minutes, then back on.
Any thoughts would be appreciated.
Regular Guest
Well, the Heat Pump shut off again between 1:00pm and 5:15pm today. I am waiting to find out what my dealer is going to do.
It is a 900 series t-stat.
Professional Member*
20 kW strip heat with a 3 ton heat pump? Don't think you need that. Not in OR.
Keep us posted on what the dealer finds. I have a similar system (4 ton), and aux heat is only needed at cold outdoor temps (i.e., <35 deg), and even then only periodically as it maintains temp (I believe the factory setting is 5 cycles per hour [CPH] for auxiliary heat). The communicating thermostat cycles the heat strips in stages based on demand, and there is a CPH setting that can be adjusted. How large is your home (sqft)?
Like duckman said, I also did not want the 950 thermostat due to issues with the TAM8. The 900 thermostat is a fine, fully functional communicating thermostat. Understand that what you're seeing may be normal. The 3 ton ZM 20 is rated at ~34,000 btuh @ 47 deg F and ~27,400 btuh @ 37 deg F. Depending on your size home, setback conditions, outdoor air infiltration, etc., it could very well be normal for the thermostat to briefly cycle heat strips in an attempt to maintain setpoint, although with a 3000 sqft home and 4 ton HP in Maryland, I don't see auxiliary heat at 40+ deg F outdoor temp. Was a load calculation done on your home prior to sizing the new equipment? What is the total heat loss of your home (btuh) at design conditions?
Your system is under warranty. The refrigerant charge could be confirmed. Do you know if your installer charged the system using the automated ChargeAssist feature?
Last edited by RyanHughes; 01-28-2013 at 10:25 PM.
Professional Member*
Good to no that it is a 900 T-stat. We had no problems with that t-stat on XL 20i with variable speed comm. air handler. FYI Trane and American standard are the same so when you see me post Trane in the fourm I am talking about the same unit. You probley already caught that but wanted to be sure to state this.Originally Posted by RyanHughes
Ryan brings up some interesting points. 20kw for (3) ton system? Maybe 15 kw staged but without a load I am just assuming this is sized to big? That unit is designed to be charged with charge assist to ensure proper charge. This is one of the easiest units to charge if instructions are followed.
I am curious to see what the Feild tech support person along with the dealer come up with. As you have been doing keep a time line on how it has ran and is running. This can help them figure out what is going on with the system.
Side note/thoughts: I just wonder if the unit is wired to bring on all the aux. heat 20 kw at once and not wired to be staged? So when the t-stat and outdoor unit since that aux. heat is needed it is bringing on all 20 kw and possiable kicking out on overload on inside unit? Also what size breaker or breakers do you have for the system. If not sized properly for 20 kw should be tripping them once aux heat comes on. Just a thought though.
I must also agree with Ryan in that the system might be operating find to some degree but with the temps you are having I see no reason if set up properly why aux heat is coming on that fast with temps in the 40's. I have only seen my aux heat come on twice this year in my home with heat pump. I would recommend with any system specialy a heat pump to not use set backs. Find a set temp and leave it. One thing is if you like to sleep at say 65 degrees and get up and adjust t-stat to say 70. The unit would bring on aux heat to warm the house up as the t-stat will see that the heat pump can't bring that temp up that fast. It will bring on both till the point that the t-stat and units reach a certain temp then the heat pump will only run with the indoor unit fan motor on. So the aux heat (heat pack) will turn off at that point.
Please keep us posted as I know there is nothing worse then having a brand new top of the line system installed that is not working right. Just hang in their once field tech support person gets there with installer they should be able to figure out the problem. As this is his job to look for things that the installer might have missed or not thought of yet.
Regular Guest
The heats strips were sized down to 15 KW and supposed to be wired to be staged. We did not have the power to the unit required to operate the 20 KW strips and our previous unit had 15 KW strips so I figured it would be fine to install the 15KW strips in the new unit instead of the 20 KW.
Our home is 2050 sq feet and fairly well insulated and sealed. I believe a load calculation was done. I do not know heat loss of the home.
I do not know if the unit was charged with the charge assist. I was at work when that was done, but I will find out.
Unfortunately, the breakers are not tripping. That would be too easyThe breaker I referred to in earlier posts was the breaker on the indoor unit. It doesn't trip though. I observed the tech turn the unit off there when checking the unit after the 89 and 91 codes so that is where I have been "resetting" the unit.
I have to work during the day so it is difficult to log very much information, but I am attempting to keep an eye on it when I am home. It seems to be operating less on the heat strips and I have been checking to see if it is defrosting when I have been able to see it is operating on the strips. The last couple times that I noticed it was on the strips it was also defrosting. If the high pressure sensor and low pressure sensor wires were hooked up backwards could that cause the unit to operate the heat strips when it didn't need to? Unfortunately, the outside temp came up about the same time the wires were hooked up properly and the unit seems to be running less on the strips so it is hard to tell if it was the lower outside temp or the wiring that caused the issue.
Ryan- when you say the heat strips are set at the factory to cycle 5 times per hour do you mean when there is a need for aux heat to be on they will cycle 5 times per hour? I'm not following you on this.
I do set back the temp 2 degrees at night to 68 from 70. Temp set point is 68 from 10:00pm to 12:00 noon, 70 from noon to 1:00pm, 68 from 1:00 to 5:00pm, 70 from 5:00 to 10:00pm. Do you recommend leaving the set point at 70 all afternoon or is dropping to 68 fine? My dealer told me that with the learning and communicating thermostat that I can turn down the set point even further at night and the thermostat will bring up the temp slowly and not use the heat strips unless it is very cold outside. Is this true?
Thank you for all of your help with this. The information has been very helpful. I will keep you posted on how things progress.
Professional Member*
On average, yes. That is the basic function of the CPH setting. However when it is very cold out and the thermostat needs the auxiliary heat to approach the setpoint, demand overrides the CPH setting and the auxiliary heat will run longer cycles as needed. Effectively the CPH setting controls the amount of temperature droop allowed. Less CPH = less cycles longer in duration, and vice versa. I mentioned this not because I think it's a root cause of your problem but because you indicated you were noticing short cycles of auxiliary heat, and depending on what your installer left the CPH setting at, it may not be irregular to notice shorter cycles.
While we can throw out ideas here, this truly seems like an issue that will require an experienced technician working with your equipment to determine why it is bringing on the heat strips when the outdoor ambient temp is only in the 40s. Some people have their electric heat locked out well below those temperatures (so they wouldn't operate until the temperature was below 30 degrees, for instance -- the 900 thermostat has this capability and it may be an option you want to explore). I would also say to just keep an eye on it yourself. Your system has only be up and running for 10 days, so the thermostat may still be learning the needs of the house and the capabilities of all heat stages as it tunes its internal PID loop (its temperature control algorithm).
Good luck in resolving the issue, and thanks for keeping us posted.
Last edited by RyanHughes; 01-29-2013 at 05:58 PM.
Regular Guest
Thanks for the info Ryan. Is there a more desirable setting for the CPH? I will be keeping an eye on it-once it is actually up and running. It keeps throwing code 89 and 91 and shutting off. There will be a tech here in the next day or two that can hopefully shed some light on that issue and will hopefully be able to diagnose the heat strip issue as well.
Professional Member*
I would leave as is. The thermostat "auto discovers" the factory settings Trane/AmStd. has programmed. I just checked the manual again, and it looks like for electric heat, the defaults are 3 CPH for stage 1 and 5 CPH for stages 2 & 3. I see no reason to change these settings (I left mine at default). Perhaps someone will offer a different opinion.
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