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Old 02-22-2019, 11:53 AM   #1
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Please help me diagnose this !!


So, got a brand new 2-ton, Trane, R410A condenser, new air handler, and new flex duct, installed 6 months ago. Old line set was pressure tested OK (500psi) during installation, new prog. T/S installed (by me), and the system worked fine through the remaining of the SoCal summer, with the T/S set to 75F.

Started working fine in the mild SoCal winter (T/S set to 74F) but 2 weeks ago the following events transpired:

Feb 7:
8AM: cold air (measured 42F) blowing out of supply vents. Inspected condenser and saw nothing "frozen", turned system on and off several times with no luck.
11AM: Set the T/S to 76F and warm air started blowing again but only made it to 74F and then started blowing cold air again. Turned system off.
12PM: Set T/S to 78F, warm air blowing again. Worked fine after this.

Feb 12:
9AM: cold air from air vents. Re-installed old, basic, non-prog T/S: heat restored, all worked fine.

Feb 17: Re-installed original, prog. T/S to use advanced features: works fine, T/S setpoint 74F, 104F from air vents, 76F at return air.

Feb 19:
7AM: cold air from vents, re-installed old, non-prog. T/S, worked fine for 1 hour.
8AM: cold air (42F) from vents again, turned system off.
9AM: found that the large (C) wire (from the relay in the A/H cabinet) was not making good connection inside the wire-nut with the other 2 small brown wires (from T/S and to the condenser). Tightened all 3 wires, warm air coming from vents again (105F). Re-installed original, prog. T/S, works fine.

Feb 22, 6:30AM: cold air from vents again.

So, I am guessing that either, the loose C wire caused some damage, or that the refrigerant charge was not set correctly, or that the reversing valve is sticking intermittently. My main observations are that the thermostats seem to be working fine, the outside fan is working, the indoor blower is working, BUT it is intermittently blowing the cold air from outside.

What do you think? Currently using space heaters and waiting for the installer to call me back but I would like to get your perspective on this. TIA for any replies.

Last edited by paul_k; 02-22-2019 at 11:58 AM.
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Old 02-22-2019, 01:03 PM   #2
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Re: Please help me diagnose this !!


When it blows cold, you have to see what mode of operation it's in. It could be defrosting but the aux heat isn't coming on to temper the air.

Need meter to troubleshoot and may need to be done live - best to call the company that installed it out.
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Old 02-22-2019, 09:15 PM   #3
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Re: Please help me diagnose this !!


Quote:
Originally Posted by user_12345a View Post
When it blows cold, you have to see what mode of operation it's in.
By "mode" you mean, in heating, or cooling, or defrost, or ... ??

Quote:
Originally Posted by user_12345a View Post
It could be defrosting but the aux heat isn't coming on to temper the air.
Are you referring to the Aux heat in the Air Handler? If so, this is a single-stage, air-to-air heat-pump without any electric strips, since they are not normally needed in these mild winters.
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Old 02-22-2019, 09:36 PM   #4
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Re: Please help me diagnose this !!


Quote:
By "mode" you mean, in heating, or cooling, or defrost, or ... ??
Have to see what it's doing.

Could be defrosting or reversing valve is in cooling position when it shouldn't be.

Does the outdoor fan motor continue to run when it blows cold?

Naturally, it will blow cold during defrost cycles but shouldn't last more than a few minutes.
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Old 02-22-2019, 10:50 PM   #5
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Re: Please help me diagnose this !!


It sounds like its defrosting. Either the termination sensor fell off, otherwise not sensing right, simply ignored by the board, or actually working just right, and you're not waiting long enough.

Call the original company back out. This sounds like warranty.

Cheers!

Last edited by supers05; 02-22-2019 at 11:01 PM.
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Old 02-23-2019, 07:14 AM   #6
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Re: Please help me diagnose this !!


Instead of being a temperature hawk regarding the temps coming out of the vents at different times and modes. Why not just set it and forget it for a day or two and see how the set point holds at various places before breaking out the digital thermometer. Heat pumps are much different than ever day fossil fuel Heat and Air units. Defective thermostat?
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Old 02-23-2019, 07:41 AM   #7
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Re: Please help me diagnose this !!


Have you monitored your electric bill to determine if the new unit has saved the heating cost as advertised?
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Old 02-23-2019, 10:23 AM   #8
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Re: Please help me diagnose this !!


Quote:
Originally Posted by COLDIRON View Post
Instead of being a temperature hawk regarding the temps coming out of the vents at different times and modes. Why not just set it and forget it for a day or two and see how the set point holds at various places before breaking out the digital thermometer. Heat pumps are much different than ever day fossil fuel Heat and Air units. Defective thermostat?
Has nothing to do with the thermostat.

A unit can also have problems and waste energy due to defrosting too long, not having the cycle terminate at the correct time based on coil temp so it's unwise to just ignore it.
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Last edited by user_12345a; 02-23-2019 at 10:38 AM.
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Old 02-23-2019, 10:45 AM   #9
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Re: Please help me diagnose this !!


Thanks everyone for the replies. It happened again at 6:30AM this morning and this time I let it run but it only lasted about 30 minutes. Previously I always turned the system off after 10 or 15 minutes of cold air because I felt there was something wrong. If this is typical of heat pumps in unusually cold weather (for SoCal, that is) then I am OK with it, since it is not a comfort problem, unless it blows cold air for several hours. It just doesn't seem normal to me, specially for a brand new system, and the installer is coming Monday morning but this intermittent behavior may not repeat when he is here. Please see comments below:

Quote:
Originally Posted by user_12345a View Post
Could be defrosting or reversing valve is in cooling position when it shouldn't be. Does the outdoor fan motor continue to run when it blows cold?
Naturally, it will blow cold during defrost cycles but shouldn't last more than a few minutes.
I only checked the outside fan the first time I noticed cold air from the vents and it was running but I didn't check it all other times.

Quote:
Originally Posted by supers05 View Post
It sounds like its defrosting. Either the termination sensor fell off, otherwise not sensing right, simply ignored by the board, or actually working just right, and you're not waiting long enough.
I didn't notice frost on the outside coil the one time I checked but I may have missed it. So far it seems to me that the only way to get cold air from the outside (~41F at the vents) blowing inside for 30 minutes is if the defrost cycle is running too long and the outdoor fan keeps running, both of which tell me something is wrong during the defrost cycle (???)

Quote:
Originally Posted by COLDIRON View Post
Instead of being a temperature hawk regarding the temps coming out of the vents at different times and modes. Why not just set it and forget it for a day or two and see how the set point holds at various places before breaking out the digital thermometer. Heat pumps are much different than ever day fossil fuel Heat and Air units. Defective thermostat?
Do you mean change the T/S set point for a day or two and see if the issue persists? As far as having a defective T/S, that was the first thing that occurred to me so I tried the old, non-prog, basic T/S but I still got the cold air behavior. It is still possible to have 2 bad T/S's but are we talking about a defective T/S just sending the wrong "O" signal to the reversing valve or also some other signal or voltage being wrong?

Quote:
Originally Posted by SeniorSitizen View Post
Have you monitored your electric bill to determine if the new unit has saved the heating cost as advertised?
I didn't have any expectations of lower heating (or cooling) costs since my 27-year old system hadn't been working at all for the last 2 years. During those 2 years I was running 2 small space heaters (720 sq ft condo) and my heating bills were significantly lower than with the old heat pump. So far this winter, based on 2 electric bills, it still costs somewhat more to run the new heat pump than 2 space heaters, but not enough to offset the benefits and convenience of running the HP. No such choice in the summer of course and that is the main reason for using the heat pump.

Quote:
Originally Posted by user_12345a View Post
Has nothing to do with the thermostat.
A unit can also have problems and waste energy due to defrosting too long, not having the cycle terminate at the correct time based on coil temp so it's unwise to just ignore it.
Is there a way to simulate or force a defrost cycle at the condenser in case it doesn't happen naturally when the installer is here?

Last edited by paul_k; 02-23-2019 at 10:56 AM.
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Old 02-23-2019, 10:52 AM   #10
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Re: Please help me diagnose this !!


Quote:
So far this winter, based on 2 electric bills, it still costs somewhat more to run the new heat pump than 2 space heaters, but not enough to offset the benefits and convenience of running the HP.
You were probably keeping most of the house cooler, running just two space heaters.

The heatpump should save a lot compared to straight resistance central heat. In a milder climate, could save 50% or more.

-------------

Something's wrong with the unit. It's abnormal for the outdoor fan to run during a defrost cycle. When it is running, it should be heating.

Either it's not shutting the fan during defrost or the reversing valve is going into the cooling position during a heating cycle for reason other than defrost.

Defrost is a/c mode with the outdoor fan motor off; it uses heat from the house and waste compressor heat to warm the coil and melt any ice.

The board has a relay which shuts the fan off. The cycle is normally initiated every 90 minutes or so of run time when the defrost thermostat is closed.

It terminates after a max time delay or the defrost thermostat opens, whichever comes first.

Some units may have demand defrost instead of timed which is more complex and uses thermisters rather than a defrost thermostat.

Yes, there's a way to simulate a defrost cycle but I can't advise without the make and model number, every board will be a little different. the manuals for most are easily found online.
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Last edited by user_12345a; 02-23-2019 at 10:55 AM.
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Old 02-23-2019, 11:21 AM   #11
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Re: Please help me diagnose this !!


You don't have to see frost for it to enter defrost.

You may have wired the thermostat up wrong. Post a picture of the thermostat wiring along with the model number of the thermostat and the heat pump.

Most units do have a defrost test function. Like user said, we need the model number.

Cheers!
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Old 02-23-2019, 11:23 AM   #12
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Re: Please help me diagnose this !!


Quote:
Originally Posted by user_12345a View Post
You were probably keeping most of the house cooler, running just two space heaters.
it's only a 2-room condo so 1 space heater in each room was plenty.

Quote:
Originally Posted by user_12345a View Post
The heatpump should save a lot compared to straight resistance central heat. In a milder climate, could save 50% or more.
If you mean strip heaters inside the A/H, there are none. There may have been other factors in the higher electric bills when the HP runs.


Quote:
Originally Posted by user_12345a View Post
Something's wrong with the unit. It's abnormal for the outdoor fan to run during a defrost cycle. When it is running, it should be heating.

Either it's not shutting the fan during defrost or the reversing valve is going into the cooling position during a heating cycle for reason other than defrost.

Defrost is a/c mode with the outdoor fan motor off; it uses heat from the house and waste compressor heat to warm the coil and melt any ice.

The board has a relay which shuts the fan off. The cycle is normally initiated every 90 minutes or so of run time when the defrost thermostat is closed.
So far it has only happened early in the morning and only during unusually cold temps in the last few weeks. Could these conditions cause the defrost thermostat to close?

Quote:
Originally Posted by user_12345a View Post
It terminates after a max time delay or the defrost thermostat opens, whichever comes first.

Some units may have demand defrost instead of timed which is more complex and uses thermisters rather than a defrost thermostat.

Yes, there's a way to simulate a defrost cycle but I can't advise without the make and model number, every board will be a little different. the manuals for most are easily found online.
Just in case, condenser is Trane 4TWR4018G1000AB, so it's 1.5 ton not 2 ton. I will try to find the schematics online but if you have any suggestions on simulating the defrost cycle I would appreciate it if you could share.
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Old 02-23-2019, 11:49 AM   #13
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Re: Please help me diagnose this !!


Quote:
Originally Posted by supers05 View Post
You don't have to see frost for it to enter defrost.

You may have wired the thermostat up wrong. Post a picture of the thermostat wiring along with the model number of the thermostat and the heat pump.

Most units do have a defrost test function. Like user said, we need the model number.

Cheers!
from top to bottom:
  • Old T/S wiring (Emerson/White-Rodgers UNP310: RC/RH jumpered inside T/S; reversing valve set to "O" in configuration menu).
  • New T/S wiring (AprilAire 8600: blue jumper is between RC and R terminals, internal equipment type switch set to "HP").
  • New T/S screen.
  • Trane condenser tag.

System works fine in cooling and heating modes, most of the time. Recent intermittent cold air issue, in heating mode, with both thermostats.

Thanks.
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Please help me diagnose this !!-old_ts_wiring.jpg   Please help me diagnose this !!-new_ts_wiring.jpg   Please help me diagnose this !!-new_ts.jpg   Please help me diagnose this !!-trane_model.png  
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Old 02-23-2019, 11:54 AM   #14
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Re: Please help me diagnose this !!


I am glad to hear you have a HVAC Tech coming Monday. That's the only true way to get your unit repaired. Please keep us in the loop after the repair . We can all learn by hearing from the on site Tech. Good luck.
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Old 02-23-2019, 01:16 PM   #15
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Re: Please help me diagnose this !!


Quote:
So far it has only happened early in the morning and only during unusually cold temps in the last few weeks. Could these conditions cause the defrost thermostat to close?
Yes.

The thing is, it should be shutting the fan during a defrost cycle and the cycle should be short.

There may be an issue with the defrost board. Or another problem causing the reversing valve to be in cooling position.

It needs to be tested when it's cold enough for defrost cycles to occur - run through heating and defrost cycles.

Reversing valve and o wire connections should be checked.

Trane/american standard may very well have demand defrost - their units are premium.
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Last edited by user_12345a; 02-23-2019 at 01:20 PM.
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