So, thanks to a friend, I acquired two nonworking CA-2-B16 cooling units. One of them was seized and the other ran but had poor cooling efficiency. It seemed so-so when we first got it going, and in the heat of the moment happiness, didn't realize it was very weak. While working on another identical CA unit, it was apparent that it had orders of magnitude greater cooling than the one which is the subject of this thread.

The symptoms were as follows when started from ambient temp, after crankcase heater was on overnight:

-Immediate excessive burbling and blowing sound from evaporator. Similar to blowing bubbles in a drink with a straw.

-Long time to develop frost (20 - 30 minutes).

-Frost was not hard, could easily wipe off with hand.

-Would not get cold enough to cycle the control off.

-Low heat at condenser and dome.

There was some rattle from the compressor, which I am not completely sure is resulting from this problem. In an attempt to address the rattle, I added some oil to the unit, however it did not make a difference in the sound or the cooling.

Thanks to the loyal Monitor Top enthusiasts I hang out with, lots of information is available on the float valve and capillary tube conversions. I read through several write-ups; and purchased a roll of capillary tube and some fittings, as a contingency plan if I was not able to repair the float valve.

I tore down a burned out CA last year, and took apart the float. The float valve seat assembly was showing severe wear. The orifice was oblong and jagged. The needle tip, however, was still pristine. Using the seat from this machine, I experimented with methods to re-cut the orifice. In the end, a diamond abrasive grinding point from Harbor Freight was just right.  This is shown in a cut-away view. IT had been reamed already before making the cutaway. I reamed it pretty heavily, as I tried several different tools before settling on the one shown previously. The first tool put chatter marks on the seat and I reamed them away with the final tool I chose. I estimate that half the amount of material was removed form the actual seat in the running unit.

Then I moved on to the unit I wanted to save. The repairs were done with the unit charged, but inerted with nitrogen on top of the methyl formate charge.  I connected the service kit and used nitrogen to "break" the vacuum and prevent air from going in and mixing with the methyl formate. This would prevent creating an explosive mixture inside the system.

I cleaned up and prepared to cut the seat off the bottom of the float chamber. I did all the cleaning before opening the system to minimize charge loss and contamination.

Once the seat was moved away from the float, I could see the worn orifice. Then the cutting tool gets used. It is a very fine cutting tool. There will be some fine brass dust from this, which some may enter the system. I could have cut the line below the seat and made more attempt to clean it, but in the condition of this unit, it didn't seem necessary. If it were someone else's machine I would have taken more precautions. Although, I doubt that the resulting debris will have any significant effect on the unit.

As for shortening the tube; one of the measurements I wanted to make was how much "stroke" the needle has from float-fully-up to float-fully-down position. It has a very small range of motion; around 3/16 inch. After cutting the tube, I pulled the needle to the down position manually. Then, when I placed the seat back in position, it did not touch the needle tip. There's a chance that the tubing cutter displaced metal sideways and "lengthened" the tube from its pre-cut dimension. However, after taking the section out, the needle would definitely touch the seat. After re-cutting the seat, there was about 1/8 inch of inward movement of the needle when the seat was placed in position.  This should give some wear tolerance before the float is resting on the bottom of the chamber without pressing the needle down; while still allowing enough travel to open the valve adequately.

The unit didn't want to work when first started up after the repairs. I have a feeling that the heater having been off during the repairs, along with the manually added NCG's (the nitrogen); it was not circulating. I had to purge it quite a lot before it started flowing refrigerant into the evaporator. It had me worried that I had blocked the system somehow. I'll be interested to see how it does tomorrow when started up. I have the heater on overnight, as well as the NCG purging is already done.

It seemed like a possible repair attempt worth trying. I only stood to lose a little time, solder, and maybe some methyl formate. As well, I was prepared to do the cap tube conversion if this wasn't feasible.

It's hard to know how much better or worse the float system is versus a capillary tube. We all seem to "know that all CA's have a bad float valve" by now. What is not clear is how long they ran originally before the float valve went out. While I do like the simplicity of capillary tube systems, there are benefits to the float design as well. Because it isn't a pre-calculated restriction; it has the ability to regulate as necessary to meter only liquid to the evaporator, at the rate it's being condensed. This gives the unit the ability to adapt to different ambient conditions, supply frequencies, compressor wear level,  and even different refrigerants.

So, if the float lasted 30 years then started leaking and deteriorated from there; maybe my repair job would give it another 20 years? We really don't know because it's all conjecture. But for a cheap and easy repair it seemed like a worthwhile thing to do. It was literally these steps:

-Add nitrogen.

-Two tubing cutter cuts.

-Ream the seat.

-One solder joint.

-Run and make NCG purge.

 II didn't video the actual repairs because this was the first time and experimental for me. The videos show the lead-up to the repairs, including borescope of the inside of another CA unit; and then the repaired float operation.

Part 1:

Part 2:

Hope you guys find this interesting!

Sincerely,

David

Thanks Brian.  Yeah, these are 85 years old this year.... Kind of hard to imagine the original engineers' thoughts about how long they would last.

Hi Ralph. Yeah, these early designs are amazing in their intricacies and designs. That's one of the reasons I so enjoy working on them.

Yeah, that's the heater I was referring to!  On both of these units, the heaters were bad. I had to make a special "heater removal tool" which was a specially ground steel rod. The tip has a point which will break up the old ceramic heater, while the sides of the rod are not sharp enough to cut into and possibly puncture the heater well.

The replacement heaters I use have come from two suppliers. One is Nordic Sensors. They sell them in smaller quantities but the cost is more.  Then there is another supplier (can't remember the name at the moment). Several of us Monitor Top collectors and repairers made a group buy of these heaters. They are the stainless steel type like what you describe.

The Monitor Top fridges before the CK designation all require a heater*. Without the heater, these will collect refrigerant in the oil shortly after startup, and potentially seize the compressor. It's very important to measure resistance of the heater and be sure it's working before powering on a "newly rescued" Monitor Top fridge! The heater should be around 1000 ohms, measured at the power cord with the fridge control in the OFF position.

* - There was a very, very early model of the DR type which has no heater, but as far as I know, they are all pretty well museum pieces now.

Hi Stan. Thanks for the kind words. I really appreciate it. 

As for the CK wiring, I don't think I've done a "start to finish" repair video on the rewiring. There are so many good picture-based threads in the MT forum already.  

There is this one: 


but I believe a lot of the repair process is glossed over. 

Hope this helps!

Sincerely,

David