My box doesn't get cold - now what do I do - Can this be made a sticky?

[MrMark]

For those coming to this board for help in solving what is wrong with their refrigeration system, I would like to address a few things they can investigate before posting to the board. Not that they wouldn't get help anyway, but it sure saves a lot of time and energy for all involved, and may offer a quicker path to getting your system up and running.

To begin with, identify the components that make up the refer system - a compressor, a condenser coil, a condenser fan motor, most often a bullet drier but then sometimes a desiccant drier, an evaporator, an evaporator fan motor, a cap tube, a suction accumulator (at the evaporator discharge), and a suction line. The compressor, condenser coil, and condenser fan all make up a module that I refer to as the "deck" or condenser.

I'm not going to go into how all these parts work as there are many sites on the web that explains the process. I should also point out that anyone accessing the refrigeration system must be certified by the EPA for the safe use and handling of refrigerants. Investigating a leak is probably OK for the lay person, but anything beyond that requires certification.

Typically what is found with these old boxes is they have lost refrigerant. Back in the day, steel lines were used for the hot gas line, as well as the condenser coil. Steel rusts, and for these old boxes that are 40+ years old, that rust has permeated the thickness of the tubing to the point that the R12 has begun to seep out. This rusting was further aggravated by the fact that the manufacturers often used a filler rod for making the soldered connections that contained phosphorus. Phosphorus attacks the steel as well as the rust, leading to the aforementioned leaking.

When inspecting a box that has cooling problems, always look to see if someone has placed a clamp-on style service port. It will either be on the suction line, or the process line (the stubbed out line coming out of the compressor.). It is my 35+ years of HVACR work opinion that clamp-on's are either leak, or will soon leak. They should be removed from the system anytime they are found.

To help identify the source of a leak, always look for a wetted area on the refrigeration piping. The wetting comes from the refrigeration oil that has seeped out thought the pores created as indicated above. Start with the hot gas line (the smaller line leading from the compressor to the condenser) as this is the highest refrigerant pressure in the system when the compressor is running.
Use a little soap and water to identify the leak if you don't have a leak detector handy. Inspect closely as the porosity of the tubing as a result of rust or phosphorous will cause micro sized bubbles to appear wherever the leak is, if that is the cause of the leak. Also keep in mind that the amount of refrigerant that is remaining in the system will have some impact on how much pressure can be developed to help in identifying leaks. If enough of the charge is lost, it is possible that air can be drawn into the system, depending on where the leak is. Air contains moisture in vapor form, and both will harmfully affect the long term operability of the system.

If a clamp-on line tap is found, it is very likely there was/is a refrigerant leak. And check around the clamp-on for signs of oil.

Once the leak is found, then the following outlines the procedure of repairing the leak and getting the box back into chillin some refreshments -

1) Reclaim/recover any remaining refrigerant. Remember, this MUST be performed by an EPA certified technician!
2) Repair the source of the leak. If replacing steel lines, then rather than using a phosphorus based solder, use prefluxed brazing rod. An alternative is to braze a coating onto the steel to protect the steel, then use silphos to make the final joint, using a lower temperature torch that will not melt the brazing.
3) Replace the liquid line drier with a Sporlan (or equal) 032-S, 032-CAP, or 032-S-T drier. Take care when cutting the cap tube. If you don't have a cap tube cutter, use a small 3 corner file and score the cap tube right against the strainer or drier that it is currently attached. Break the tube at the score line by bending back and forth. But make certain the score is deep enough not to cause you to collapse the cap tube in any way.
When removing the existing strainer or drier from the condenser tube, do so by cutting the tube, or again with the 3 corner file scoring. The reason -  heating a drier causes what it has caught to be out-gassed back into the system again. You want to minimize the infiltration of any of those contaminants back into the system.
4) Repair any places in the system where a clamp-on may have been placed. Purge the system with dry nitrogen in order to minimize/eliminate carburizing the heated copper. It is impossible to seal a system under pressure, but by purging dry nitrogen through the system, it forces all the atmosphere out, and under 0 psi, the atmosphere inside the system will be almost pure nitrogen. Welding can then be done with minimal issue.
5) Remove the original process tube from the compressor if it is not long enough to use as a process tube again. The idea here is to have a tube long enough that a schraeder valve can be installed, the system charged, the tube can be pinched off with vice grips, the schraeder valve removed, and the open end of the tube where the schraeder was located can be sealed with silphos.
6) Pressure check the system with nitrogen. This is where the "Test Pressures" or the pressures listed on the machine come in. Unless otherwise indicated, the pressures listed on the machine are the test pressures the components were tested at, and those pressures are usually well above the normal operating pressures. Since it is impossible to isolate the evaporator from the condenser to perform this test at the indicated pressures, generally if you can apply and maintain 200-250 psi, you will be good to go. Again, use dry nitrogen (or other recommended dry, inert gas) for this test. If leaks are indicated, bleed off the test gas to 0 psi, and make repairs as needed.
7) Triple evacuate the system - the first evacuation will remove remnant nitrogen or test gas, and if all is good, you should easily get down to 1000 microns - Note, you can't read microns with a set of dial gauges. You MUST use a micron gauge (again, a certified technician will have a micron gauge.). Break this vacuum with clean nitrogen or recommended test gas and evacuate again to 1000 microns. If you can't reach and hold 1000 microns, either the system is still "wet" with moisture (from having been open to the atmosphere for a long time, or from a leaky system). Continue to evacuate until you reach and can hold 1000 microns. Break this vacuum with the refrigerant that is to be used in the system. Evacuate the system to 500 microns or less. Insure that the system will hold at no more than 500 micron (many manufacturers recommend 250 microns. The deeper the vacuum held, the longer the long term service life of the system.).
8 ) Recharge the system with the recommended amount and type of refrigerant. Most of these systems charge with around 16 ozs or R12. The amount will be indicated somewhere on the unit data plate, or a data plate on the condensing deck itself. The charge MUST be weighed in to insure proper cooling operation. Design values for superheat and sub-cooling are unknowns. There are some typical values that would be seen, but they are dependent on a number of other factors, such as ambient air temperature and if a liquid line tap was installed (for sub-cooling), and box temperature for superheat.
9) Once the unit is charged and running, pinch off the process tube, remove the schraeder, and seal the line as described above.

As for "Did I lose too much oil?" or "Do I need to add more oil?", there is not a way to know without completely removing the compressor from the deck, turning it over, and capturing the oil that comes out. Then measure how many ounces recovered, find out how much was supposed to come out, and replenish the compressor with that amount of oil. A pain to do at best. My experience says to not worry about it. Seal the system up to make it like new again, and let her run. Unless you just know the system has lost a lot of oil, and can guess how much it was. Too much oil in a system can interfere with compressor operation. Some say it will blind the condenser or evaporator, but with the correct refrigerant charge, refrigerant velocities will be such as to push any excess back to the compressor, where the dipper shield will be dipping into a deeper oil reserve than it was designed for.

And as for "How do I know if my compressor is going out?", well, there are some misconceptions of how hermetic compressors work. First, compressors don't have valves like are found in a 2 or 4 cycle engine. Hermetic compressor valves are reed valves like in an air compressor. For the most part, they are either good, or bad. They break when stressed and overheated due to a bad condenser fan motor, or blocked condenser. You can determine this after first insuring the motor is good and the condenser coil is clear of debris (you can normally see through the fins of these coils.). Once that is done, and if there is no liquid line schraeder valve to hook gauges up to, feel the liquid line leading back into the condenser from the cap tube. If hot to the touch then feel of the return bends going from bottom to top of the coil. You should feel a temperature change. Also, get an amprobe and measure the compressor current (amps). If the amps are low, and there is no temperature change on the coil, then it is likely the valves are shot, and you need a new compressor.
Alternatively, if you can measure the liquid pressure, then also measure the liquid line temperature. Convert the liquid line pressure to temperature for the refrigerant in the system, then subtract the refrigerant line temperature from that value. The result is "subcooling" and should be in the range of 5-15 degrees F, 5 degrees being with a higher ambient and box temperature/load, 15 degrees for a lower ambient temperature.

If the cap tube has come lose from the suction line, using tie-wraps to hold it back in place is a good alternative to soldering. The fact that it is lose is not a major player in terms of the box not cooling down. It was done for a couple of reasons - 1) To help insure no liquid was returning to the compressor, 2) to gain a little more sub-cooling in the liquid which increased the refrigerant quality, at no increase in power consumption. Not being attached to the suction line will not make the difference between a working and not working box, but in the long run, using tie-wraps or some means to reattach the cap tube to the suction line will extend the life of the refrigeration system. I have also used soft solder to reattach as was done originally at the factory.

Once you get the refrigeration side in top order, your next task is to replace the fan motors, starting with the evaporator fan motor. Remember, on most boxes, this motor runs 24/7/365, so it see's a lot of use. After 40+ years, maybe it's time for it to be put out to pasture. Next is the condenser fan motor. While it's a more robust design and does not run as much as the evaporator motor, it still is an important part of the long term reliability of your refrigeration system. If that compressor is 40+ years, the condenser fan motor going out only hastens the inevitable for the compressor.

And with that, the best of luck to you on getting your box working!