Classic HVPA & HVPSA M&S 8.09-1
15700 - 21
HVAC Equipment
Flooding (cont’d)
Problem/Symptom
Likely Cause(s)
Correction
Poor system control
using capillary tubes.
Overcharge.
High head pressures.
Evaporator air flow too low.
1.
2.
3.
Check system charge.
Dirty heat pump.
Restricted air flow.
Recirculation of air.
Adjust air flow to 400 CFM/Ton.
1.
2.
3.
Thermostatic Expansion Valves
High superheat, low
suction pressure.
Moisture freezing and blocking
valve.
Dirt or foreign material blocking
valve.
Low refrigerant charge.
Vapor bubbles in liquid line.
Misapplication of internally equal-
ized valve.
Plugged external equalizer line.
Undersized TXV.
Loss of charge from power head
sensing bulb.
Charge migration from sensing
bulb to power head (warm power
head with warm, wet cloth. Does
valve operate correctly now?)
Improper superheat adjustment
(only applicable to TXV with ad-
justable superheat settings).
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Recover charge, install filter drier,
evacuate system, recharge.
Recover charge, install filter-drier,
evacuate system, recharge.
Correct the charge.
Remove restriction in liquid line.
Correct the refrigerant charge.
Remove non-condensible gases.
Use correct TXV.
Remove external equalizer line
restriction.
Replace with correct valve.
Replace power head or complete TXV.
Ensure TXV is warmer than sensing
bulb.
Adjust superheat setting counter-
clockwise.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Valve feeds too much
refrigerant, with low
superheat and higher than
normal suction pressure.
Moisture causing valve to stick
open.
Dirt or foreign material causing
valve to stick open.
TXV seat leak (a gurgling or hiss-
ing sound is heard at the TXV
during the off cycle, if this is the
cause). Not applicable to bleed
port valves.
Oversized TXV.
Incorrect sensing bulb
location.
Low superheat adjustment (only
applicable to TXV with adjust-
able superheat setting).
Incorrectly installed or restricted
external equalizer line.
1.
2.
3.
4.
5.
6.
7.
Recover refrigerant, replace filter drier,
evacuate system and then recharge.
Recover refrigerant, replace filter drier,
evacuate system and recharge.
Replace the TXV.
Install correct TXV.
Install bulb with two mounting straps,
in 2:00 or 4:00 position on suction
line, with insulation.
Turn superheat adjustment clockwise.
Remove restriction, or relocate exter-
nal equalizer.
1.
2.
3.
4.
5.
6.
7.
