Classic HVPA & HVPSA M&S 8.09-1
15700 - 22
HVAC Equipment
Thermostatic Expansion Valves (cont’d)
Problem/Symptom
Likely Cause(s)
Correction
Compressor flood back
upon start-up
.
Any of the causes listed under
symptoms of problem 2.
1.
Any of the solutions listed under
solutions of problem 2.
1.
Superheat is low to
normal with low
suction pressure.
Unequal evaporator circuit
loading.
Low load or air flow entering
evaporator coil.
1.
2.
Ensure air flow is equally distributed
through evaporator.
Ensure proper piston.
Check for blocked distributor tubes.
Ensure blower is moving proper air CFM.
Remove/correct any air flow restriction.
1.
2.
Superheat and
suction pressure
fluctuate (valve is
hunting)
Expansion valve is oversized.
Sensing bulb is affected by liq-
uid refrigerant or refrigerant oil
flowing through suction line.
Unequal refrigerant flow through
evaporator circuits.
Improper superheat adjust-
ment (only possible with TXV
having superheat adjustment.
Moisture freezing and partially
blocking TXV.
1.
2.
3.
4.
5.
Install correct TXV.
Relocate sensing bulb in another position
around the circumference of the suction
line.
Ensure proper distributor piston is
inserted.
Ensure sensing bulb is located properly.
Check for block distributor tubes.
Replace TXV or adjust superheat.
Recover refrigerant, change filter drier,
evacuate system and recharge.
1.
2.
3.
4.
5.
Valve does not regulate
at all.
External equalizer line not con-
nected or line plugged in.
Sensing bulb lost its operating
charge.
Valve body damaged during
soldering or by improper instal-
lation.
1.
2.
3.
Connect equalizer line in proper location,
or remove any blockage.
Replace TXV.
Replace TXV.
1.
2.
3.
