Thermo King UT-1200, Manual

Page: 157 / 169

157
Refrigeration Diagnosis
Rapid c
yc
ling between Cool and Heat
Unit c
ool
s i
n Heat and Defr
os
t c
yc
le
Unit heat
s in Refrigeration (Cool) c
yc
le
High head pres
su
re
Low head pr
es
su
re
No head pr
es
su
re
High s
uc
tion pres
su
re
Low s
uc
tion pres
su
re
N
o su
ct
io
n p
re
ssu
re
Unit operating i
n a v
ac
uum
Rec
eiv
er
s
ight gl
as
s empty
Suc
tion li
ne fr
os
ting bac
k
Unable to pump down s
ys
tem
Unable to pull
v
ac
uum in l
ow s
ide
Unable to hold v
ac
uum i
n low s
ide
N
oisy
co
mp
re
ss
or
Unit not refr
iger
ati
ng
Unit not heating or defros
tin
g
Sym
p
to
m
Possible Causes
• • • • Overcharge of refrigerant
• • • • • • Shortage of refrigerant
• • • • • • No refrigerant
• Air through condenser too hot (ambient)
• Air flow through condenser restricted
• • • Air through condenser too cold (ambient)
• • • Air in refrigerant system
• Condenser fan blades bent or broken
• Air short cycling around evaporator coil
• Air through evaporator restricted
• • • • Evaporator needs defrosting
• Compressor discharge check valve leaking
• • Scroll compressor seals leaking
• Too much compressor oil in system
• Faulty oil pump in compressor
• Loose compressor pulley
• Compressor bearing loose or burned out
• • • • • Broken discharge check valve in compressor
• • Expansion valve power element lost its charge
• • • Expansion valve feeler bulb improperly mounted
• • • Expansion valve feeler bulb making poor contact
• • Expansion valve open too much
• • Expansion valve closed too much
• • Expansion valve needle eroded or leaking
• • • Expansion valve partially closed by ice, dirt or wax
• • • Liquid refrigerant entering compressor
• • Restricted line on the low side