Ch 7 Troubleshooting Flashcards
(55 cards)
- Cap tube system
- Low evap temp/pressure
- High superheat
- Low condenser temp
- Low subcool
Undercharged
- TXV system
- Low evap temp/pressure
- High superheat
- Low condenser temp
- Low subcool
- Bubbling sightglass
Undercharged
*does not always indicate a leak; if system was charged in warm weather it may be insufficient in cold
- Cap tube system
- high condenser temp/pressure
- high subcool
- slightly high evap temp
- normal superheat
Overcharged
*could have been overcharged in the cold, or mistakenly with normal sightglass bubbling
- cap tube system
- high condenser temp
- normal subcool
- high evap temp/pressure
- low to no superheat
Condenser airflow problems
- TXV system
- high condenser temp
- about normal subcool
- slightly higher evap temp
- normal superheat (unless extreme)
Condenser airflow problems
- cap tube system
- high condenser temp
- high subcool
- high evap temp
- low to no superheat
Noncondensables
*pulling a vacuum and weighing in refrigerant will prevent contamination
- TXV system
- high condenser temp
- very high subcool
- normal or slightly high evap temp
- normal or slightly low superheat
Noncondensables
- large system
- high side head pressure remains high for a few minutes after the compressor is turned off
noncondensables
- large system
- with refrigerant at ambient temps, condensing temp based on head pressure does not match chart psig at ambient
noncondensables
- cap tube system
- low condensing pressure
- normal subcool
- high evap pressure
- high superheat
inefficient compressor
- TXV system
- low condenser discharge pressure
- normal subcool
- high evap suction pressure
- high superheat
inefficient compressor
what is the primary indicator of an inefficient compressor?
higher than normal suction pressure WITH lower than normal head pressure
How can you check a compressor through vacuum testing?
It will be unable to hold a vacuum for more than a few minutes before the low side gauge rises. This does not show compressor damage from broken connecting rod or bearing wear. Use spec sheets to check amperage pull against pressures and temps
How can you identify a fully blocked cap tube?
- evaporator in vacuum
- head pressure and subcool indicate the presence of refrigerant in the condenser
- cap tube system
- low evap temp/pressure
- high superheat
- low condensing temp
- high subcool
Partially restricted cap tube
*does not increase head pressure
What are the possible causes of high head pressure on a cap tube system?
- high ambient temp
- condenser airflow problems
- overcharge
- TXV system
- low evap temp/pressure
- high superheat
- low condenser temp
- normal subcool
- clear sightglass
Partially restricted TXV
- TXV system
- low evap temp/pressure
- high superheat
- low condenser temp
- normal subcool
- bubbling sightglass
- temperature drops drastically across liquid line
Restriction in liquid line after the receiver
*most commonly a kink or a filter drier in need of replacement - more than a 3 degree F drop across the filter drier indicates replacement
-TXV system
-low evap temp/pressure
-high superheat
-high condenser temp/pressure
-high subcool
bubbling sightglass
restriction in the liquid line before the receiver
*very rare, most likely @ the receiver inlet. only other location is condenser U-bends
- cap tube system
- low evap temp/pressure
- low or no superheat
- low condenser temp/pressure
- normal subcool
Evaporator problems
*some superheat at the compressor suggests the refrigerant is vaporizing in the suction line but not in the evaporator
- TXV system
- low evap temp/pressure
- low to normal superheat
- low condensing temp
- normal subcool
Evaporator problems
What are the signs of evaporator oil logging?
- a history of not maintaining temperatures
- symptoms don’t fit with other issues
- TXV hunting, floodback, or can’t adjust superheat
- some U-bends near the evap outlet aren’t sweating or frosting like others
- history of compressor changes
- sight glass oil level varies a lot through cycle
- noisy or vibrating compressor
- evidence of flooding or slugging
- absence of a pump-down solenoid on a remote commercial refrig condensing unit
- freezer has only one defrost
- evidence of incorrect piping practices: no p-trap with compressor above evap, suction lines not sloped or too large
- diagnosis w/o pressure gauges
- low subcool
- low evap ΔT
- low condenser ΔT
undercharged
- diagnosis w/o pressure gauges
- slightly high subcool (7-10F)
- low evap ΔT
- low condenser ΔT
- suction line is only slightly cool
stopped cap tube
