REFRIGERATION AND AIR CONDITIONING
Technical information
Fault Location on
PL, TL, NL, FR Compressors
COMPRESSORS
This Hermetic Note is directed especially to the service network, for household appliances and similar. For detailed information on compressors see the
data sheets.
Compressors type PL, TL, NL, FR and partly SC are equipped with a PTC
starting device (fig. 1) or a relay and start capacitor (fig. 2). The motor protector
is built into the windings.
In the event of a start failure, with a cold compressor, up to 15 minutes can
elapse before the protector cuts out the compressor.
When the protector cuts out and the compressor is warm, it can take up to 1
hour before the protector cuts in the compressor again.
The compressor must not be started without the electrical equipment.
Before beginning systematic fault location, a good rule is to cut the supply
voltage for at least 5 minutes. This ensures that the PTC starting device has
cooled off and is ready for start.
A voltage drop or blackout within the first minutes of a pull down of the
appliance with cold compressor, can lead to an interlocking situation. A
compressor with PTC can not start at non equalized pressure and the PTC
does not cool down so fast. It can take more than 1 hour until the appliance
then operates normally again.
To avoid unneccessary protector operation and consequent waiting time, it is
important to carry out fault location in the sequence given below. Tests are
made according to desriptions on following page.
• Remove electrical equipment
• Check electrical connection between main and start pins of compressor
terminal
• Check electrical connection between main and common pins of
compressor terminal
• Replace compressor, if above connection checks failed
• Else, replace electrical equipment
If the compressor still does not operate, most probably it is no electrical
compressor failure. For more detailed fault location, see the tables.
General
Fault location
Electrical compressor
quick check
Fig. 1: PTC starting device Fig. 2: Starting relay
Fault location table :
Most common fault reasons, detectable before dis-mounting compressor.
Customer
claim
No/reduced
cooling
First analysis
Compressor
does not run
Compressor
runs 100%
Compressor
runs on/off
Possible cause
Compressor gets no
or bad power supply
Defective starting
equipment
Compressor with PTC
can not start at
pressure difference
PTC defective
Relay defective
Compressor
overloaded
Defective motor
windings
Defective protector
Mechanically blocked
compressor
No or low refrigerant
charge
Too high ambient
temperature
Too high condensing
temperature
Capillary partly
blocked
Valves coked or
damaged
Thermostat not OK
Wrong refrigerant
charge
Ice block built up on
evaporator
Compressors trips on
motor protector
Check
Voltage at plug and fuse
Aplicance energized
Thermostat function
Cables and connections in appliance
Voltage at compressor terminals
Relay function by shaking to hear if
armature is working
Start capacitor function
PTC by shaking
PTC resistance 10 to 100 Ohm
between M and S pin
Stop time long enough for pressure
equalization
PTC resistance 10 to 100 Ohm
between M and S pin
Relay function by shaking, to hear
moving of armature
Condenser pressure and ventilation
Ambient temperature too high
according to type label of appliance
Check winding resistances
Check protector with ohmmeter
Start with proper starting equipment, voltage and conditions,
windings and protector OK
Recharge and search for leaks
Ambient temperature according to
type label of appliance
Condenser and compressor
ventilation
Recharge and search for leaks,
measure suction pressure. Capillary
blocked, if pressure very low
Recharge and search for leaks
Thermostat type and function
Recharge and search for leaks
Check for ice on evaporator
Thermostat function and settings
Internal no-frost fan function
Compressor load, compressor and
condenser ventilation
Compressor voltage supply for
minimum 187 V
Compressor voltage supply for drop
outs. Check thermostat and appliance cables for loose connections
Motor windings resistance for partly
short circuit or earth connection
Activity
(depends on result)
Replace relay
Replace start capacitor
Replace if noise appears
Replace PTC
Adjust thermostat
difference
Replace PTC
Replace relay and
capacitor
Ensure proper ventilation
Replace compressor
Replace compressor
Replace compressor
Ensure leakfree system
and proper charge,
replace drieer
Ensure proper ventilation
and wall distance
Replace compressor, if
still not cooling properly
Replace thermostat
Ensure leakfree system
and proper charge,
replace drier
Defrost properly
Replace thermostat
Ensure proper ventilation
and wall distance
Ensure proper power
supply
Fix all connections
Replace compressor
Customer
claim
Noise
Fuses are
blown by
appliance
First analysis
Rattle or
humming
Banging at
start or stop of
compressor
Relay clicking
frequently after
start
Short circuit in
appliance
Short circuit in
compressor
Fuse blows at
compressor
start
Starting capacitor exploded
Starting relay
cap blown off
Possible cause
Tube touching cabinet
Compressor touching
cabinet
Broken internal
suspension spring or
discharge tube
Resonance
Fan noise
Compressor block hitting housing internally
Compressor overloaded
Relay defective
Defective cabling in
appliance
Defective thermostat
Ground connection
Defective terminals
Short circuit between
cables at terminals
Short circuit in
compressor motor
Supply voltage too
low
Fuse loaded by too
many appliances
Resettable fuse too
quick acting
Partly short circuit to
earth
Defective relay
Wrong relay type
Extremely many starts
and stops of compressor
Short circuit in compressor motor
Check
Tube placing
Compressor mounting and rubber
feet
Listen to compressor with screwdriver against compressor with edge
and to your ear with grip
Find vibrating mounting parts
Vibration of fan or fan mounting
Compressor overload by pressure
Fan function
Refrigerant charge
Pressure equalization before start
and number of on/off cycles
Ambient temperature according to
type label
Ventilation to compressor and condenser. Check fan function
Right relay type for compressor
All connecting cables and power
supply cord for loose connections,
short circuits
Thermostat connections
Resistance from line/neutral to earth
For burns on the terminal pins
Connectors and cables at compressor
Resistance values in windings
Resistance between terminals and
earth
Supply voltage at compresor start
>187 V
Total fuse load
Fuse load and type
Resistance between terminals and
earth
Relay function by shaking, to hear
moving of armature
Relay type
Relay type
Thermostat defect or differences too
small
Compressor motor resistances
Activity
(depends on result)
Bend tube to their right
place, carefully
Place rubber feet and
mounting accessories
correctly
Replace compressor, if
abnormal sounds
Place or fix correctly
Fix fan and blade, replace,
if defective
Clean condenser if dusty.
Make sure, that ventilation
gaps for air circulation are
satisfactory
Recharge, if too high
Adjust thermostat, if stop
time less than 5 min
Take appliance out of
function, if ambient too
hot
Clean condenser if dusty.
Make sure, that ventilation
gaps for air circulation are
satisfactory
Replace relay, if wrong
Fix connections properly
Fix connections properly
Replace electrical
accessories
Insulate cables and
connectors
Replace compressor, if
short circuited
Connect applaince to
different fuse
If possible replace by
slightly slower type
Replace compressor, if
short circuited
Replace relay and
capacitor
Replace relay and cap
Replace relay and cap
Adjust or replace
thermostat
Replace compressor
Resistance between pins M (main) and S (start) on compressor terminals is
measured with an ohm-meter, see figure 3.
• Connection: Main and start
windings normally OK
• No connection: Main or start winding
defective: Replace compressor
At cold compressor (ca. 25°C) the values are ca. 10 to 100 Ohm for 220-240 V
compressors. For partial short circuit detection, exact values are needed from
data sheets of the specific compressor, which can be found on the Danfoss
Compressors homepage.
Resistance between pins M (main) and C (common) on compressor terminals
is measured with an ohm-meter, see figure 3 and 4.
• Connection: Protector OK
• No connection: Compressor cold: Protector defective: Replace
compressor
Compressor hot: Protector could be
OK, but cut out: Wait for reset
Remove relay from compressor.
Measure connection between connectors 10 and 12 (see figure 5):
• No connection: Relay defective: Replace relay
Measure connection between connectors 10 and 11:
In normal vertical position (like mounted, solenoid upward):
• Connection: Relay defective: Replace relay
• No connection: OK
In top-down position (solenoid downward):
• Connection: OK
• No connection: Relay defective: Replace relay
Remove PTC from compressor.
Shake by hand. Pin C can slightly rattle.
• Internal rattle
noise
(except pin C): PTC defect: Replace PTC
Measure resistance between pins M and S, see figure 6.
Resistance value between 10 and 100 Ohm at room temperature for 220 V
PTC.
• Connection: PTC working: OK
• No connection: PTC defect: Replace PTC
Check main and
start winding
Check protector
Check relay
Check PTC
Fig. 4: Windings and protectorFig. 3: Compressor terminals
Fig. 5: Relay connections Fig. 6: PTC connections (backside)
Danfoss can accept no responsibility for possible errors in catalogues, brochures and other printed material. Danfoss reserves the right to alter its products without notice. This also applies to
products already on order provided that such alterations can be made without subsequential changes being necessary in specifications already agreed.
All trademarks in this material are property of the respective companies. Danfoss and the Danfoss logotype are trademarks of Danfoss A/S. All rights reserved.
Danfoss Compressors GmbH
Mads-Clausen-Strasse 7
Postfach 1443, D-24939 Flensburg
Telefon: (0461) 4941-0
International +49 461 4941-0
Telefax: +49 461 44715
Telex: 227 43 dancom d
CN.71.B5.02
Produced by Danfoss G1 Advertising Agency 01.07.UF.JN.AO
www.danfoss.com/compressors
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