: Service Manual
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20
Refrigeration System
Refrigerant
In an air conditioning and heat pump system, refrigerant transfers heat
from one replace to another. The condenser is the outdoor coil in the
cooling mode and the evaporator is the indoor coil.
In a heat pump, the condenser is the indoor coil in the heating mode and
the evaporator is the outdoor coil.
In the typical air conditioning mode, compressed hot gas leaves the
compressor and enters the condensing coil. As gas passes through the
condenser coil, it rejects heat and condenses into liquid. The liquid
leaves condensing unit through liquid line and enters metering device at
evaporator coil. As it passes through metering device, it becomes a
gas-liquid mixture. As it passes through indoor coil, it absorbs heat and
the refrigerant moves to the compressor and is again compressed to hot
gas, and cycle repeats.
Compressor Oil
Brazing
This section on brazing is not intended to teach a technician how to
braze. There are books and classes which teach and refine brazing
techniques. The basic points below are listed only as a reminder.
Definition: The joining and sealing of metals using a nonferrous metal
having a melting point over 800°F/426.6°C.
Flux: A cleaning solution applied to tubing or wire before it is brazed.
Flux improves the strength of the brazed connection.
When brazing is required in the refrigeration system, certain basics
should be remembered. The following are a few of the basic rules.
1. Clean joints make the best joints. To clean:
– Remove all oxidation from surfaces to a shinyfinish before brazing.
– Remove all flux residue with brush and water while material is still
hot.
2. Silver brazing alloy is used on copper-to-brass, copper-to-steel, or
copper-to-copper. Flux is required when using silver brazing alloy.
Do not use low temperature solder.
3. Fluxes should be used carefully. Avoid excessive application and do
not allow fluxes to enter into the system.
4. Brazing temperature of copper is proper when it is heated to a
minimum temperature of 800°F (426.6°C) and it is a dull red color
in appearance.
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 tubes.
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.
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.
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.
WARNING
!
UNIT OPERATION AND SAFETY HAZARD
Failure to follow this warning could result in personal injury or
equipment damage.
R-410A refrigerant which has higher pressures than R-22 and other
refrigerants. No other refrigerant may be used in this system. Gauge set,
hoses, and recovery system must be designed to handle R-410A. If you
are unsure consult the equipment manufacturer.
CAUTION
!
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment damage or
improper operation.
The compressor in a R-410A system uses a polyolester (POE) or
polyvinyl ether (PVE) oil. This oil is extremely hygroscopic, meaning it
absorbs water readily. POE/PVE oils can absorb 15 times as much
water as other oils designed for HCFC and CFC refrigerants. Take all
necessary precautions to avoid exposure of the oil to the atmosphere.
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