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Cold Liquid Line & Bottom Coils

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BPet

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Hi, I noticed that our AC unit was not cooling well and determined that the copper liquid line going into the air handler, which is in a closet in the upstairs hallway, is very cold when the AC is running. I removed the front panel of the unit, and the smaller liquid lines feeding the coil get frosty when the unit is running. The bottom few inches of the coil also becomes cold, but the top 75% of the A frame coil is not cold at all. On the outside unit, the air leaving the top of the unit is also ambient temperature, it is not warm like it is normally. Replaced the capacitor on the outside unit just in case, but that did not help. Any suggestions on what could be the possible issue would be greatly appreciated. (The unit is a 3.5 ton and 12 years old.) Thanks in advance for any suggestions.
 

kok328

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going to be an issue with the freon level in the unit and/or the TXV.
only way to tell is to put gages on the unit and see what's going on.
 

BPet

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Thanks, I will have gauges in a few days and I'll report back. Thanks!
 

BPet

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As I'm learning about how to add refrigerant, I'm trying to determine what the Subcooling value should be on my unit. It is not listed on the tag on the outside unit. I found information in the product manual that indicates:
"Design Subcooling 7 +/- 2° F @ the liquid service valve: ARI 95° F test conditions"
Do I need to be concerned with the "ARI 95° F test conditions" or can I consider a subcooling value of 5-9°F acceptable on my system?

Thanks again!
 

BPet

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Also, do you use a vaporizer for r410A or do you just open and close the valve in short bursts?
 

kok328

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As I'm learning about how to add refrigerant, I'm trying to determine what the Subcooling value should be on my unit. It is not listed on the tag on the outside unit. I found information in the product manual that indicates:
"Design Subcooling 7 +/- 2° F @ the liquid service valve: ARI 95° F test conditions"
Do I need to be concerned with the "ARI 95° F test conditions" or can I consider a subcooling value of 5-9°F acceptable on my system?

Thanks again!
You'll need to reference an appropriate PT chart if your not 95 degrees.
 

kok328

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Also, do you use a vaporizer for r410A or do you just open and close the valve in short bursts?
short bursts and wait for gages to catch up. vaporizer if you going to invert your tank for quicker charging.
 

BPet

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I checked the system pressures/temps this morning. System Recap: 3.5 Ton HeatPump, 12 Year Old Unit, R410A with TXV, Mfg. Target SubCool 7°F +/- 2°F @ 95°F Outside Temp
Today's Outside Temperature: 80°F, Ran System 15 Min prior to recording measurements, no sweating on Suction Line.
Gauge Low Pressure Side: 82 PSI ~22°F, Suction Line 81°F - so SuperHeat of 59°F
Gauge High Pressure Side: 215PSI ~72°F, Liquid Line 80°F - so I guess that is a negative Subcooling: - 8°F

Is it possible that the system has a slow leak? I know we had it leak tested a few years back because it had lost some refrigerant; however, the leak was not found and it was only a small amount of refrigerant and so the thinking was that we recharge and see what happens. Its been a few years and we have 3 other AC units and this one is in the master bedroom. I think there has been a tiny leak for a long time and the unit has been very slowly leaking R410A this entire time. I don't think it was noticeable because we have other units, and we have the thermostat to raise the temperature during the daytime, and the temperature is lower at night so the unit does not have to be working perfectly in order for our bedroom temp to be fine. I think it may have just lost enough refrigerant to go over the tipping point to what was acceptable to where we are now. I would not even have noticed except that I noticed the unit running more often at night and then I felt the liquid line and it was cold, not warm.

or is that not a possibility?

Thanks again for any information you can provide! :)
 

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