Troubleshooting With Superheat - Bryant Base Series Application Manual And Service Manual

Residential Air Conditioners and Heat Pumps Using R-22 and Puron® Refrigerant: Application Guideline and Service Manual

TROUBLESHOOTING with SUPERHEAT

This troubleshooting routine was developed to diagnose cooling
problems using superheat in TXV systems. It is effective on heat pumps
in cooling mode as well as air conditioners. The system must utilize a
TXV as the expansion device in cooling mode.
Basic Diagnostics
NOTE: When checking refrigerant charge and troubleshooting
operating systems, the indoor airflow has significant effect on the
determination. If you are at this stage, it is assumed you have already
checked the subcooling once and believe the charge is correct. From this
point, the airflow must be verified prior to proceeding, hence step 1
below.
1. Check or verify proper indoor airflow
• Indoor air filter
• Duct dampers and supply registers are open
• Indoor coil for debris
2. Check subcooling at OD unit liquid service valve
• Outdoor airflow (debris on coil, etc.)
• Set the subcooling at value listed on rating plate if standard
lineset
• Set the subcooling at the maximum of 10°F or value listed on
rating plate if a long line application
3. Check superheat at OD unit vapor service valve.
• If low (< 2°F), proceed to Low SuperHeat section.
• If between 2 and 20°F/11°C valve is probably operating properly.
• If greater than 20°F/11°C, perform Pseudo Evaporator SuperHeat
Instructions check as follows:
- Check refrigerant pressure at vapor service valve and
refrigerant temperature at outlet of evaporator.
- Use suction line geometry (diameter and equivalent length),
unit capacity and Tables 7 and 8 to determine suction pressure
drop.
•For standard lineset diameters (vapor service valve diameters
and larger) and lengths (less than 80 ft), generally no pressure
adjustment (per Table 6
•For longer (greater than 80 ft) and small diameter linesets (less
than service valve size), correct pressure (add to gauge pressure
reading) per Table 6 and
• If Pseudo Superheat is greater than 15, proceed to High SuperHeat
section.
• If Pseudo Evaporator Superheat is between 2 and 15, TXV appears
to be functioning properly.
• If operation erratic (hunting), proceed to Hunting Superheat °F
Superheat in repetition section.
NOTE: Hunting is when the valve superheat swings more than 10°.
Low Superheat with Normal or Low Suction Pressure
NOTE: Normal or low suction pressure is considered for
R-22: < 80 psig, Puron: < 135 psig
1. Re-check airflow and then check sensing bulb tightness,
orientation on vapor tube and is properly wrapped. If OK proceed
to Step 2
2. Check superheat at vapor service valve and Pseudo Evaporator
Superheat.
• If both are less than 2°F, TXV likely not controlling properly, i.e.
stuck open -> REPLACE VALVE
• If superheat is higher than 15°F, proceed to Step 3
3. Perform TXV function check.
• With system running, place sensing bulb in ice bath for ~1 minute
-> superheat should increase.
– If no response, Replace Valve
– If OK proceed to Step 4
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
or Table 7) is required.
Table 7.
4. Check for even temperature distribution at outlet of each circuit of
evaporator
• If greater than 15°F between circuits, distributor or coil has a
restriction.
• If OK proceed to Step 5
Low Superheat with High Suction Pressure
NOTE: High suction pressure is considered for R-22: > ~80 psig, Puron:
> ~135 psig. An application issue or other system component failure
typically causes this condition.
5. R-22 Systems: Check that proper valve used (not an R-410A valve)
• If OK proceed to Step 6
6. Check airflow, sensing bulb tightness, orientation on vapor tube
and ensure bulb is properly wrapped.
• If OK proceed to Step 7
7. Check that compressor is pumping properly
NOTE: Loose Rules of Thumb: Is discharge saturated ~20°F higher
than ambient temperature? Is discharge superheat between 15 and 50?
• If OK proceed to Step 8
8. Recheck Airflow and Subcooling.
• If OK proceed to Replace Valve
High Superheat with Normal or Low Pressure
NOTE: Normal or low suction pressure is considered:
R-22 < 80 psig, Puron < 135 psig.
9. Check for restriction in liquid line (kinked line, filter drier
restricted, etc.)
• If OK proceed to Step 10
10. Check for restriction in suction line (kink, restricted suction filter
drier etc.))
• If OK proceed to Step 11
11. Check power element cap tube is not broken
• If OK proceed to Step 12
12. Check that equalizer tube is not kinked or plugged
• If OK proceed to Step 13
13. Check that inlet screen (R-22 systems) is not restricted
• If OK proceed to Step 14
14. Replace Valve
High Superheat with Normal or High Suction Pressure
NOTE: Normal to High suction pressure is considered
for R-22: > ~65 psig, Puron: > ~110 psig. An application issue or other
system component failure typically causes this condition.
15. Check airflow, sensing bulb tightness, orientation on vapor tube
and ensure bulb is properly wrapped.
• If OK proceed to Step 16
16. R-410A Systems: Make sure proper valve is used (Not R-22)
• If OK proceed to Step 17
17. Check for even temperature distribution at outlet of each circuit of
evaporator
• If OK proceed to Step 18
18. Check for high evaporator load: Return Air Leaks, high indoor wet
bulb and/or dry bulb temp, undersized system, etc.
• If OK proceed to Step 19
19. Check that compressor is pumping properly
• Loose Rule of Thumb: Is discharge saturated ~20°F higher than
ambient temperature? Is discharge superheat between 15°F and
50°F?
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