Carrier 25VNA Service Manual page 35

6. Remove power from indoor and heat pump unit prior to ser-
vicing unit. The EXV will retain the open position.
NOTE: See service training materials for troubleshooting the EXV
using EXV CHECK mode.
FIELD
SIDE
SEAT
BAR STOCK FRONT SEATING VALVE
Fig. 28 – Suction Service Valve (Front Seating)
NOTE: All outdoor unit coils will hold only factory- -supplied
amount of refrigerant. Excess refrigerant, such as in long- -line
applications, may cause unit to relieve pressure through internal
pressure- -relief valve (indicated by sudden rise of suction pressure)
before suction pressure reaches 5 psig (35kPa). If this occurs, shut
unit off immediately, front seat suction valve, and recover
remaining pressure.
Reversing Valve
In heat pumps, changeover between heating and cooling modes is
accomplished with a valve that reverses flow of refrigerant in
system. This reversing valve device is easy to troubleshoot and
replace. The reversing valve solenoid can be checked with power
off with an ohmmeter. Check for continuity and shorting to
ground. With control circuit (24v) power on, check for correct
voltage at solenoid coil. Check for overheated solenoid.
With unit operating, other items can be checked, such as frost or
condensate water on refrigerant lines.
The sound made by a reversing valve as it begins or ends defrost is
a "whooshing" sound, as the valve reverses and pressures in system
equalize. An experienced service technician detects this sound and
uses it as a valuable troubleshooting tool.
Using a remote measuring device, check inlet and outlet line
temperatures. DO NOT touch lines. If reversing valve is operating
normally, inlet and outlet temperatures on appropriate lines should
be close to each other. Any difference would be due to heat loss or
gain across valve body. Temperatures are best checked with a
remote reading electronic- -type thermometer with multiple probes.
Route thermocouple leads to inside of coil area through service
valve mounting plate area underneath coil. Fig. 29 and Fig. 30
show test points (TP) on reversing valve for recording
temperatures. Insulate points for more accurate reading.
If valve is defective:
1. Shut off all power to unit and remove charge from system.
2. Remove solenoid coil from valve body. Remove valve by
cutting it from system with tubing cutter. Repair person
should cut in such a way that stubs can be easily re- -brazed
back into system. Do not use hacksaw. This introduces
chips into system that cause failure. After defective valve is
removed, wrap it in wet rag and carefully unbraze stubs.
Save stubs for future use. Because defective valve is not
overheated, it can be analyzed for cause of failure when it is
returned.
3. Braze new valve onto used stubs. Keep stubs oriented
correctly. Scratch corresponding matching marks on old
valve and stubs and on new valve body to aid in lining up
new valve properly. When brazing stubs into valve, protect
valve body with wet rag to prevent overheating.
STEM
SERVICE PORT
W/SCHRADER CORE
A91447
4. Use slip couplings to install new valve with stubs back into
system. Even if stubs are long, wrap valve with a wet rag to
prevent overheating.
5. After valve is brazed in, check for leaks. Evacuate and
charge system. Operate system in both modes several times
to be sure valve functions properly.
TO OUTDOOR
COIL
TP- -4
FROM COMPRESSOR
DISCHARGE LINE
Fig. 29 – Reversing Valve
(Cooling Mode or Defrost Mode, Solenoid Energized)
TO
FROM
ACCUMULATOR
OUTDOOR
COIL
TP- -4 TP- -3
INSULATE FOR
ACCURATE
READING
FROM COMPRESSOR
DISCHARGE LINE
THERMOMETER
Fig. 30 – Reversing Valve
(Heating Mode, Solenoid De- -Energized)
WARNING
!
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal
injury or death.
Before installing, modifying, or servicing system, main
electrical disconnect switch must be in the OFF position.
There may be more than 1 disconnect switch. Lock out and
tag switch with a suitable warning label.
35
FROM INDOOR COIL VIA
SERVICE VALVE ON
OUTDOOR COIL
TO
ACCUMULATOR
TP- -3 TP- -2
TP- -1
A88342
TO INDOOR COIL
VIA SERVICE VALVE
ON OUTDOOR COIL
INSULATE
FOR
TP- -2
ACCURATE
READING
TP- -1
ELECTRONIC
A88341