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Discussion Starter · #1 · (Edited)
Hi, I have a Trane XL15i Heat Pump that seems to be generating less heat this winter (although it still does generate some heat although it seems to feel cooler than last winter). It is currently 40 F outside (humidity 85%), and it seems that every time it runs it ends up going into defrost mode about 30 minutes later which is probably ok given the high humidity?. I removed the panel cover and noted that the green LED was flashing 3 times per second. Normally it flashes 1 time per second, although I never verified it before in the winter. I had observed it earlier during the summer.

To test, I powered down the furnace (air handler) and the heat pump through my breaker panel, and then powered both back up. The LED at this point on the heat pump started flashing once per second (normal operation). I then increased the thermostat temps so that the heat pump can run. I observed, after about 10 minutes, frost covered the liquid line (after the Thermal expansion valve -TXV, I can see it through the grill), and some frost (but not too much) I could see on some areas (but very few perhaps 3 rows on one side) of the spine fins. After about 30 minutes, the system went into defrost mode, and the LED lights immediately began flashing 3 times per second. After about 5 minutes, the defrost operation completed, and the heat pump reversed and began normal heating operation. I could see that the defrost was gone, but LED lights kept flashing 3 times per second.
So it seems like everything seems to be normal except for the LED flashing 3 times per second, and the lower heat output.

I checked the demand defrost control checkout sheet from the unit, and it indicates that 3 flashes per second is:

635076


I am not sure I understand Fault B? Does that mean that the defrost took the maximum time? In any case, since I powered off/on the unit, does that basically rule out Fault B, since only 1 defrost cycle was executed after power on.

The Fault C (High Delta T) has a number of possible causes:
1) SOV stuck in heating we can rule out since the unit completed defrost successfully
2) OD fan motor failure or OD fan on in defrost can also be ruled out
3) I haven't verified the sensors but I am guessing they are ok since it is going into defrost mode and coming out of it?
4) Closed Txv, I guess unlikely since unit is still producing heat and also go into cool for defrost mode?
I guess that leaves that the unit is undercharged? But then why does it only detect this when it goes into defrost mode?

Thanks for any help, guidance.
 

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Discussion Starter · #3 ·
Thank you for your reply beenthere, do you mean Fault B or C comes up because it takes too long for the unit to defrost? I didn't time it specifically, but it seemed to be defrosting only for a few minutes (seemed like less than 5 minutes). But the code appeared when it went into defrost, not when it finished
 

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Discussion Starter · #5 ·
The temperature of the heat coming out of one of the registers is about 74 degrees Fahrenheit. I read somewhere it should be higher than this, closer to 90 degrees? I will check the sensors tomorrow
 

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Discussion Starter · #6 · (Edited)
I measured both the ambient and coil sensors with the unit off for a couple of hours. i.e. both sensors should be at outdoor temperature. The temperature outside was 44 F with humidity at 70%.
The ambient measured 22.6 KOhms, and the coil measured 23 KOhms which corresponds to ~ 44 F. So sensors are good. Unit still goes into defrost after about 15 minutes of operation with the 3 LED flashes, it then takes 3 minutes to fully defrost. Undercharged unit? I am hearing gurgling sounds when the unit shuts off, and the register temperature is only about 73 F.
Pictures of the frost below on liquid line after TXV, and only on one side of unit.

635196

635204


635205
 

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Discussion Starter · #9 ·
Technician came and verified that the system was on low charge and verified that it wasn't the TXV. Luckily he ended up finding the leak on one of the small copper distribution tubes after the TXV. He brazed the leak with silfoss, and after all said and done got the heating working again optimally (I see around 86 degrees at the register with 32 F ambient outside). After he left, my inquisitive nature had me verifying his work where I noticed an air bubble right next to the place where he fixed it (he had placed some leak detector liquid to check for the leak). I removed the bubble with my finger and it didn't come back. However, I took a hand liquid soap dispenser and sprayed some around the area. I could see a small bubble forming and popping, then forming and popping very slowly. I called the company back, and they will come back next Monday to verify this. I am wondering, should this whole part be replaced? Is it normal for distribution tubes to develop leaks after only 6 years in operation?
 

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It happens once in a while. Replacing distributor tubes and manifold isn't always an easy task. Its easier just to braze it.
 

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Discussion Starter · #11 ·
ok thank you. He has said something about vibration may have caused it. Its the small tube touching the larger one that had the leak. He removed the tie wrap and separated the tubes apart.
635490
 

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Discussion Starter · #13 ·
technician came back, saw the leak, and did the following:
1) closed off the suction and discharge valves coming from the air handler (ones at the entry point at the heat pump)
-- there were a few other steps prior to this which I didn't understand, he started the heat pump with the gauges on, and stopped it as soon as it hit a certain reading -- not sure what
2) loosened the valves (both the high and low pressure ones) inside the unit to remove the refrigerant (he took some kind of reading prior to that)
3) Put some nitrogen flowing in, re-brazed the leak
4) filled it up with nitrogen at 400 psi to check for leaks (none were found, used the leak detector fluid)
5) removed the nitrogen, then used a device to remove the moisture, etc for about 10 minutes
6) then once the system checked out, he closed the valves, re-opened the entry valves
7) then put his gauges on the high and low pressure valves inside the unit to verify the charge
8) He consulted the service fact sheet that shows for a given outdoor temperature what the pressures should be
9) He added a little more refrigerant (didn't seem like the same amount that he took out) and the pressures more or less matched the service fact sheet (temperature outside was 27 degrees Fahrenheit, service fact shows liquid line pressure of 76, and 300 for that temperature and 70 degree dry bulb (the indoor temperature from the thermostat was 67). The PSIs he stooped at were 76 PSI, and 315 PSI. He did check the temperature of the liquid line which was at 72 degrees F

Is this an OK way to verify the charge during winter? Shouldn't he have re-couped the refrigerant instead of dumping it in the environment, and measured the amount he took out and put the same back in?
 

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Discussion Starter · #15 ·
Maybe he pumped the charge into the indoor unit by turning on the heat pump and then closing the valves? He did open the internal valves and let them bleed for a while after that. I heard a hissing sound for about 5 minutes. I assumed this was refrigerant he was leaking out so he could braze the pipe. Perhaps by turning on the heat pump, he pumped most of the charge into the air handler, closed off the valves so none would come back into the heat pump, and then bled off the little that was remaining?
 

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Discussion Starter · #17 ·
Ok thanks. One last question. There was a black thin plastic film on the left side of the heat pump covering about 1/3 of the coil. The technician immediately removed it saying that it is not needed? Do you know what purpose it served?
 

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Ah, protects the joints of the aluminum coil. A lot of them don't have that cover. So its not 100% needed.

Originally I was picturing some huge black thing covering the entire left side of the coil. lol
 
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