Merry Christmas! Very nice work! You said you had to purge non condensibles, where do you think they were hiding during your evacuation process? Especially since you now have low and high side ports. What wattage and voltage heater are you using?
Hi Allan. Merry Christmas to you as well! Thankfully, we're having a nice warm spell here in AL this week, which is a gift in and of its self this time of year. All the better to be working on fridges.
As for the NCG's - that's a tough one. I have a few theories. One is that by putting N2 in the machine and then running the compressor to circulate it - it was in the cylinder and lubrication lines internal to the compressor. With the oscillating cylinder design, it MAY be that, if the crankshaft is in a certain position, the cylinder is effectively blocked off from evacuation because the ports are closed.
Another theory is, that the cans of R152A were manufactured with NCG in them due to poor quality control, or some other manufacturing reason. R152A is easy to get in small cans, or in a one cubic meter tote - but not in the common "Freon tanks" like we have for other refrigerants. I did quite a lot of research with this when it was first suggested as an automotive refrigerant. The Office Depot and Ultra Duster cans did not have any NCG when tested. But those were the only brands tested.
Last theory is that my vacuum pump or gauges had a leak. The leak was on the pump its self or the hoses between the pump and manifold gauge. This allowed the vacuum to be incomplete, but to hold where it was and not leak down after the valves were closed. I bought a brand-new micron gauge last year, but it leaks out-of-the-box and I have not had any resolution with the seller. At that time I was operating without a precise vacuum gauge. The system volume is so large that a tiny residual pressure would leave significant air remaining.
I can't rule out the above. The micron gauge was an extremely frustrating issue, leading me down a rabbit hole of parts changing on one repair. I ended up replacing the isolation valve and fittings on the vacuum pump, as well as my gauge hoses. I don't know for sure if any of those parts were leaking since, in the end, the micron gauge was at fault.
More recently, I charged a DR1 which required 1 or 2 purges then after that has worked perfectly for weeks.
The laws of physics are very unkind to high-side dome / high-side float machines when it comes to NCG's and restrictions or traps of any sort in the high-side. For the float to open, liquid must be in the float chamber. For the liquid to move into the chamber to lift the float, there has to be flow toward the chamber. The only way liquid can move towards the float chamber while the needle valve is closed, is by whatever gas in in the float chamber either compressing and reducing in volume; or condensing to liquid and allowing liquid to flow into the space it occupied. Because the high-side dome compressor housing has so much volume, the system won't build enough pressure to "force" liquid into the float by compressing NCG's. The high side dome will provide a receiver which buffers the pressure and causes the refrigerant to stay in the dome and, eventually, condense in the dome. The pressure differential between the compressor dome and the float chamber is extremely small by design. It only takes a small difference in pressure to make refrigerant condensation favor one area over another. So, if the float chamber has NCG's in it, the condensation of the refrigerant will happen in the dome, before it will build pressure to overcome and compress NCG's in the float chamber.
So to summarize - A high-side dome / high-side float machine is likely to suffer when presented with any level of NGC's; even low levels which would be no issue for another system configuration.
As for the heater, it's a 60W 240V heater. Same as a 15W 120V heater. Ohm's law, of course.
The machine came with a 15W heater. When running it with this heater, there was some noise to the compressor. Not the classic "sick DR rattle" but a sort of "ever-changing and slightly elevated sound level." This was 100% cured by installing the heater boost transformer and raising the wattage to 60.
I know there's some concern the heater wattage is too high. A 40w should have been adequate; but the 60 is what was available. Several of us have experimented and found out that the DR compressors like hot oil. They operate quieter and the power consumption is less with higher wattage oil heaters. The oil viscosity may be lower, thereby less pumping losses and oil shear drag is happening. Or, the oil contains less refrigerant to go through the lubrication system and interrupt the oil film.
When this repair was completed, the temperature in my shop was in the mid 80's. During cabinet pull-down, the top of the dome was never too hot to touch. We also need to remember that the DR motor is not oil cooled, as is the CK. The motor is cooled by high pressure gas. I don't have a high level of concern for the motor temperature because the heater is heating the oil, which is below the motor. It seems to make the compressor mechanism run with less friction and therefore less load on the motor when the oil is warmer.
We all know that electricity cost was very high in the 20's and 30's. GE probably put the bare minimum heater in place to prevent damage during the expected life of the machine. Now that these are more valuable as antiques, the priorities may be different. It seems (based on noise and motor power use measurements) that a higher wattage heater is beneficial to the machine. I believe it's very much worth it to spend a little more for energy during the off-cycle to have a quieter machine with less friction.
Sincerely,
David