Check Expansion Valve (Heat Pumps Only) - Lennox XP25-024-230-01 Installation And Service Procedure

Check Expansion Valve (Heat Pumps only)

The thermostatic expansion valve (TEV) controls the flow of liquid refrigerant by maintaining superheat of the refrigerant
vapor at the outlet of the outdoor coil during heating mode.
CHECKOUT:
Problem
Symptoms
Superheat is too low -
valve feeds too much
Superheat is to high -
Valve does not feed or
does not feed enough
No superheat at start-
up only - valve feeds
too much at start-up
Superheat is erratic or
hunts - system hunts or
cycles
Table 14. Expansion Valve Checks
1. Liquid slugging
2. Low superheat
3. Suction pressure normal or
high
1. Evaporator temperature too
high
2. High superheat
3. Low suction pressure
1. Liquid slugging
2. Zero super heat
3. Suction pressure higher
than normal
1. Suction pressure hunts
2. Superheat hunts
3. Erratic valve feeding
Causes
1. Oversized valve
2. Incorrect superheat setting
3. Moisture
4. Dirt or foreign material
5. Incorrect charge selection
6. Incorrect bulb location
7. Incorrect equalizer location
8. Plugged equalizer (balanced
ported valve)
1. Low on refrigerant
2. High superheat
3. Flash gas in liquid line
4. Low or lost bulb charge
5. Moisture
6. Plugged equalizer (conventional
valve)
7. Insufficient pressure drop or
valve to small
8. Dirt or foreign material
9. Incorrect charge selection
10. Incorrect bulb location
11. Incorrect equalizer location
12. Charge migration
13. wax
14. Wrong equalizer type valve
15. Rod leakage (balanced port
valve)
16. Heat damaged power head
1. Refrigerant drainage
2. Compressor or suction line in a
cold location
3. Partially restricted or plugged
external equalizer (balance port
valve)
4. Liquid line solenoid will not com­
pletely shut
1. Bulb location Incorrect
2. Too large a valve
3. Incorrect superheat setting
4. System design
Page 68
Corrective Action
1. Replace with correct size valve
2. Adjust the superheat to correct set­
ting
3. Replace the filter / driers
4. Evacuate the system and replace the
refrigerant
5. Clean out the material or replace the
valve
6. Select proper charge based on refri­
gerant type
7. Relocate the bulb to proper location
8. Relocate the equalizer to proper loc­
ation
9. Remove any restriction in the equal­
izer tube
1. Add correct amount refrigerant
2. Change superheat setting
3. Remove source of restriction
4. Replace power element or valve
5. Replace driers or evacuate the sys­
tem and replace refrigerant
6. Remove any restriction in the equal­
izer tube
7. Replace existing valve with properly
sized valve
8. Clean out the material or replace the
valve
9. Select the correct charge
10. Move the bulb to the correct location
11. Move equalizer to correct location
12. Move valve to a warmer location or
apply heat tape to the power head
13. Use charcoal drier
14. Use externally equalized valve
15. Replace power head or valve
1. Use Pump Down Control
2. Install a trap at the top of the Evapor­
ator
3. Install Crankcase Heater
4. Install Suction Solenoid
5. Remove restriction
6. Disassemble/Clean Valve
7. Replace valve
1. Reposition bulb
2. Replace existing valve with correct
sized valve
3. Adjust superheat to correct setting
4. Redesign system
XP25