Troubleshooting the system
Unit does not start
Check disconnect , breaker or fuses. Lets not forget about that switch at the bottom of the stairs.
Check Contactor If the contactor is pulled in, then the problem is most likely a line voltage problem. If the contactor is not pulled in the problem is in the low voltage side of the unit. Check to see if the coil is energized.
Check low ambient stat. If open you can temporarily bypass it.
Check time delay relay If open you can temporarily bypass it.
Is the low pressure control open ? See low suction pressure. DO NOT BYPASS
Is the high pressure control open ? See high head pressure. DO NOT BYPASS
Insufficient Cooling
Check refrigerant charge Either an undercharge or over charge can cause this.
Is the condenser restricted ? Look for leaves, paper ect.
Is the condenser clean ? Clean it out with a garden hose. TURN OFF POWER FIRST. to clean it spray the water through the fins in the condenser.
Is there frost on the suction line ? This is usually a sign of either loss of refrigerant charge or most commonly lack of air flow. See the next questions.
Are the filters plugged ? result will be an extra cold suction line and low back pressure.
Is the evaporator clean ? result will be an extra cold suction line and low back pressure.
Do you have sufficient air flow ? result will be an extra cold suction line and low back pressure.
How many air diffusers are closed ? Too many closed will result with extra cold suction line and low back pressure.
What is your Supply air temperature ? Look for a TD of 15 to 20oF
Is the compressors drawing RLA ( rated load amps) or less ? If it's less are valves ok ? look for low head and higher than normal back pressure.
Check the compressor contactor Are the contacts welded closed
No load on the evaporator Dirty filters, closed vents, dirty coils , incorrect fan speed , all will be noted with low back and possibly frost.
Compressor valve damage Diagnosed by low head, high back and low current draw
Check refrigerant charge Overcharge will reduce the capacity of the condense Is the condenser restricted ? Look for leaves, paper ect. Is the condenser clean ? Clean it out with a garden hose. TURN OFF POWER FIRST. to clean it spray the water through the fins in the condenser. Does the fan motor seam to be running properly?
Does the system have non condensable in it? Sometimes noted by excessive subcooling or at least what appears to be according to a PT chart. Is condenser air re circulating unit under a deck or low roof
High suction pressures
Compressor Valve damage look for low head pressure and low current draw. Excessive high head pressure resulting in increased pressure drop on metering device, refer to High head pressure. Excessive Load Furnace heat on Unit too small
Low Suction Pressure Is there frost on Check refrigerant charge Either an undercharge or over charge can cause this. Is there frost on the suction line ? This is usually a sign of either loss of refrigerant charge or most commonly lack of air flow. See the next questions. Are the filters plugged ? result will be an extra cold suction line Is the evaporator clean ? result will be an extra cold suction line Do you have sufficient air flow ? result will be an extra cold suction line How many air diffusers are closed ? Too many closed will result with extra cold suction line What is your Supply air temperature ? Look for a TD of 15 to 20oF Is the outdoor air temperature too low for proper operation ? Install head pressure controls if you require low ambient operation
Is it cycling on overload Is the compressor overheating ?
Sufficient voltage at the unit ? Check charge.
Is it cycling on low or high pressure See low suction or high head
Is the unit oversized. check square footage of home
Ice or frosted Suction line
Check refrigerant charge Either an undercharge or over charge can cause this.
Are the filters plugged ?
Is the evaporator clean ?
Do you have sufficient air flow ?
How many air diffusers are closed ? Too many closed will result with extra cold suction line
Is the fan belt broke ? Look for a TD of 15 to 20oF
Is the outdoor air temperature too low for proper operation Install head pressure controls if you require low ambient operation
Compressor does not start
Check thermostat Turn fan to the on position if the furnace fan starts go check for power at the condensing unit.
Check disconnect , breaker or fuses. Replace as required
Check Contactor If the contactor is pulled in the problem is a line voltage problem. If the contactor is not pulled in the problem is in the low voltage side of the unit. Check to see if the coil is energized.
Check low ambient stat. If open you can temporarily bypass it.
Check time delay relay If open you can temporarily bypass it.
Is the low pressure control open ? See low suction pressure. DO NOT BYPASS
Is the high pressure control open ? See high head pressure. DO NOT BYPASS
Is the compressor hot ? Off on overload
Start or run cap shorted, open or blown. If unit humming check these,
Compressor hums Start or run cap shorted, open or blown, If seized try a hard start kit. do not call compressor if it is hot. Only call a cold compressor
Compressor runs non stop
Check refrigerant charge Either an undercharge or over charge can cause this.
Is the condenser restricted ? Look for leaves, paper ect.
Is the condenser clean ? Clean it out with a garden hose. TURN OFF POWER FIRST. to clean it spray the water through the fins in the condenser.
Is there frost on the suction line ? This is usually a sign of either loss of refrigerant charge or most commonly lack of air flow. See the next questions.
Are the filters plugged ? result will be an extra cold suction line and low back pressure.
Is the evaporator clean ? result will be an extra cold suction line and low back pressure.
Do you have sufficient air flow ? result will be an extra cold suction line and low back pressure.
How many air diffusers are closed ? Too many closed will result with extra cold suction line and low back pressure.
What is your Supply air temperature ? Look for a TD of 15 to 20oF
Are the low and high side the same pressure Cycle unit and to verify that the high pressure internal relief valve is not causing the problem prior to calling the compressor.
Is the compressors drawing RLA ( rated load amps) or less ? If it's less are valves ok ? look for low head and higher than normal back pressure.
Trouble shooting Trouble shooting single phase motors Troubleshooting three phase motors
