Service Manual
30
Evacuation
Proper evacuation of the system will remove
non- condensibles and assure a tight, dry system before
charging. The two methods used to evacuate a system are
the deep vacuum method and the triple evacuation method.
Deep Vacuum
Method
The deep vacuum method requires a vacuum pump
capable of pulling a vacuum of 500 microns and a vacuum
gauge capable of accurately measuring this vacuum depth.
The deep vacuum method is the most positive way of
assuring a system is free of air and moisture. (See Fig. 27.)
500
MINUTES
01234567
1000
1500
LEAK IN
SYSTEM
VACUUM TIGH
T
TOO WET
TIGHT
DRY SYSTEM
2000
MICRONS
2500
3000
3500
4000
4500
5000
A95424
Fig. 27 – Deep Vacuum Graph
Triple Evacuation
Method
The triple evacuation method should be used when vacuum
pump is only capable of pumping down to 28 in. of mercury
vacuum and system does not contain any liquid water. Refer
to Fig. 28 and proceed as follows:
1. Pump system down to 28 in. of mercury and allow
pump to continue operating for an additional 15
minutes.
2. Close service valves and shut off vacuum pump.
3. Connect a nitrogen cylinder and regulator to system
and open until system pressure is 2 psig.
4. Close service valve and allow system to stand for 1
hr. During this time, dry nitrogen will be able to diffuse
throughout the system absorbing moisture.
5. Repeat this procedure as indicated in Fig. 28. System
will then be free of any contaminants and water vapor.
CHECK FOR TIGHT, DRY SYSTEM
(IF IT HOLDS DEEP VACUUM)
EVACUATE
BREAK VACUUM WITH DRY NITROGEN
WAIT
EVACUATE
CHARGE SYSTEM
BREAK VACUUM WITH DRY NITROGEN
EVACUATE
WAIT
A95425
Fig. 28 – Triple Evacuation Method
TROUBLESHOOTING WITH
SUPERHEAT
This troubleshooting routine was developed to diagnose
cooling problems using superheat in TXV systems. It is
effective on heat pumps in cooling mode as well as air
conditioners. The system must utilize a TXV as the
expansion device in cooling mode.
Basic
Diagnostics
NOTE: When checking refrigerant charge and
troubleshooting operating systems, the indoor airflow has
significant effect on the determination. If you are at this
stage, it is assumed you have already checked the
subcooling once and believe the charge is correct. From this
point, the airflow must be verified prior to proceeding, hence
step 1 below.
1. Check or verify proper indoor airflow
S Indoor air filter
S Duct dampers and supply registers are open
S Indoor coil for debris
2. Check subcooling at OD unit liquid service valve
S Outdoor airflow (debris on coil, etc.)
S Set the subcooling at value listed on rating plate if
standard lineset
S Set the subcooling at the maximum of 10For
value listed on rating plate if a long line application
3. Check superheat at OD unit vapor service valve.
S If low (< 2F), proceed to Low SuperHeat section.
S If between 2 and 20F/11_C valve is probably
operating properly.
S If greater than 20F/11_C, perform Pseudo
Evaporator SuperHeat Instructions check as
follows:
Check refrigerant pressure at vapor service
valve and
refrigerant temperature at outlet of evaporator.
Use suction line geometry (diameter and equiv-
alent length), unit capacity and Tables 4 and 5 to
determine suction pressure drop.
S For standard lineset diameters (vapor service
valve diameters and larger) and lengths (less
than 80 ft), generally no pressure adjustment
(per Table 5 or 6) is required.
S For longer (greater than 80 ft) and small
diameter linesets (less than service valve
size), correct pressure (add to gauge
pressure reading) per Tables 5 and 6.
S If Pseudo Superheat is greater than 15, proceed to
High SuperHeat section.
S If Pseudo Evaporator Superheat is between 2 and
15, TXV appears to be functioning properly.
S If operation erratic (hunting), proceed to Hunting
Superheat
F Superheat in repetition section.
NOTE: Hunting is when the valve superheat swings more
than 10_.
Low Superheat with Normal or Low Suction
Pressure
NOTE: Normal or low suction pressure is considered for
R- 22: < 80 psig, R- 410A: < 135 psig
1. Re- check airflow and then check sensing bulb
tightness, orientation on vapor tube and is properly
wrapped.