November 5, 2007
A very common freezer repair trouble call is a frozen evaporator coil. When you open the door to inspect the coil, look around for signs of outside air migrating into the box.
Does the door close properly, and are the door gaskets in good condition and do they seal? If not, this will have to be taken care of.
Is there a layer of snow on the ceiling or floor inside the door, or anywhere else in the box? Are there large icicles hanging off the ceiling anywhere?
These are signs that air and moisture are getting into the box, and this freezer repair will involve sealing the entry points. You'll probably need to melt the ice off the coil during this freezer repair trouble call, so use the most efficient method available to you.
Check the evaporator drain pan and drain line. If the drain line is frozen solid, the pipe heater may have failed, and if so, it will have to be repaired. Wire it to be energized at all times. If the drain pan is frozen solid, check the heater in the pan. If it’s failed, it will have to be replaced.
Once the ice is melted off the coil, check the evaporator fans. Make sure they run, that they turn in the right direction, and that the blades are the right size.
If the coil has warmed up while you were melting off the ice, the fans may not run for a few minutes until the coil cools down and the fan delay closes (if there’s a fan delay in the circuit).
The next step during this freezer repair trouble call will be to check the defrost timer. Verify that it’s wired correctly, then put it into defrost manually, see if the defrost circuit energizes and stays energized, and take an amp draw on the heater circuit.
If it doesn’t cycle into defrost manually, determine why and correct the problem. Check the timer contacts and mechanism, and check the wiring.
If it does cycle into defrost, open the evaporator panels and take an amp draw on each individual heater. Repair any that aren’t working.
The last step when checking defrost problems is to set the timer near to the start time for a defrost cycle, set the cycle duration for five minutes, then wait to verify that the timer will cycle into defrost and then back into cooling after five minutes.
By the time you’ve reached this stage of a freezer repair trouble call, you should have found any problems that would cause the evaporator to freeze up.
Another possible freezer repair service call would be a unit not cooling, with a short cycling compressor.
Turn the unit off, attach your gauges, and look around for any obvious signs of a refrigerant leak. If you find a leak, or if the pressures are extremely low, the unit was probably cycling on the low pressure control, and repairing the leak should take care of the problem.
If the pressures are normal and there’s no obvious sign of a leak, run the unit and check the pressures.
If the pressures aren’t obviously high or low enough to trip the controls, get your multi tester ready, take the cover off the pressure controls, run the unit, and when the compressor cycles off, check which pressure control has opened. This freezer repair might only require replacing a failed pressure control.
If the suction pressure drops low enough to trip the low pressure control, and the pressure control is set to a normal range, check for a restricted liquid line, drier, metering device, or liquid line solenoid.
If the discharge pressure rises high enough to trip the high pressure cut out - if it’s an air cooled condenser, check for a failed condenser fan or a blocked or dirty condenser coil; if it’s a water cooled condenser, check for low or no water flow or water entering the condenser at a temperature that’s too high. For either type of condenser, check for air, noncondensables, or the wrong refrigerant in the system.
Another possible freezer repair service call might be for a unit that’s not cooling, with a compressor that runs a couple of minutes then cycles off on the oil safety switch.
First, check to see that there’s oil at the proper level in the sight glass. If not, fill with the correct oil to the correct level, and try to find out if there has been a leak in the system, or if the system has been running at low capacity for an extended period of time.
If there’s an oil separator, make sure the float valve or return line to the crankcase isn’t restricted. Attach gauges to the oil pump outlet port and the low side of the system, reset the oil safety switch, run the unit, and check the oil pump pressure and suction pressure.
If the oil pump maintains oil pressure at the correct differential, but the oil safety switch trips, the switch has failed and should be replaced.
When you run the unit after this repair, keep a close eye on the oil level as the unit loads up, and be ready to recover any excess oil.
If the oil pump doesn’t maintain oil pressure at the correct differential, you’ll have to troubleshoot the oil pump and/or the compressor. The oil pump may be worn out, or the compressor may be worn out or have a broken part internally.
Isolate the compressor, recover the refrigerant, disassemble and inspect the compressor and oil pump, and use your judgment about whether to repair them on the spot, or replace them.
Any time you’re on a freezer repair trouble call, take a careful look at all of the components, and make sure they all match the capacity of the system, and that everything is installed correctly.
Once again, are the evaporator fan motors the right size, and are the blades the right size, and turning in the right direction?
Is the filter drier the correct capacity, and actually installed in the liquid line and not in the discharge line?
Is the condenser coil in good condition, the correct size for the system, and piped correctly, with the hot gas in at the top and the liquid out at the bottom?
Is the condenser fan motor the right size, and is the fan blade the right size and turning in the right direction?
For freezer repair service calls regarding poor capacity, our System Evaluation Manual, available at http://hvacr-resource.com/System_Evaluation_Manual.html, has a cycle diagram and guidelines for troubleshooting pressures and temperatures in air conditioning and refrigeration systems. You might also be interested in taking a look at our Refrigeration and Electrical Troubleshooting Chart, available at http://air-conditioning-and-refrigeration-guide.com/support-files/refrig%20&%20elect%20t%20s%20chart.pdf, which is reprinted from a military training manual.
Publication date: 11/05/2007