[77newell]

Gordon: yes I would appreciate the information you have, it would simplify my research.

To the others that have noted that the refrigerant is low. I seem to own the mystery coach so nothing is as straightforward as it seems. The symptoms of plugged capillaries are similar to low refrigerant and tend to confuse the issue. In these small simple systems I have it is possible for all the refrigerant to condense as liquid and be held in the condenser. The liquid pressure (130ish) we measured is consistent with R22 at the prevailing temperature of the condenser at the time (68ish). The vacuum on the vapor side is an indication that a restriction MAY exist, though it could also be the result of a low refrigerant charge. The judgement of the tech was that the vapor side pressure was far lower than any low charge condition he had experienced. In addition, if the charge was low the cooling cycle would still be happening though at a much reduced amount. We could detect no cooling at all happening in the capillaries or the adjacent evaporator tubes. The belief is that with 130ish pressure on the liquid and a vacuum on the vapor side we would be able to detect some cooling if the charge was circulating.

There is one more test we will conduct prior to opening the system and trying to blow it out backwards (a 50-50 probability of success according to the service manager). The test involves monitoring the speed of pressure drop-off on the liquid side once it is pressurized and then shutting off the compressor. If it drops off fairly quickly (we may need to compare to a normally operating system) either the compressor is leaking backwards (thought to be unlikely since it pulls a strong vacuum) or the capillaries are open (and we then add refrigerant) or if it drops really slowly then the capillaries are essentially blocked and we proceed to attempt blowing out the blockage. Honestly, I'm hoping it's just a low charge, but I'm not counting on it. I'll let you know what we find.

[Richard]

here is another test you could run. compare the amperage that the compressor is pulling with one of the other three systems. If the amperage is higher then blocked tube or TXV, if the amperage is lower then low charge. tg

I SURE as heck would put 50 bucks of R22 to check low charge before I spent a LOT more rebuilding the system. Just sayin..........

ask the tech what the superheat and supercool numbers were.

[77newell]

The amps on the compressor in question is 4.6 at start-up and drops to 4.0 within a minute or so. A comparable compressor starts at 8.6, drops to 6.9 in about a minute, and then gradually rises to 11 over the course of the next 5 minutes before stabilizing. The amps used by the compressor in question suggest low flow through it.

The superheat: with suction at -2.7psi R22 boils at -45 degrees, temperature of the input pipe at the compressor was 67 degrees (essentially equal to ambient temperature), therefore the superheat would calculate to 112 degrees which is far away from the generally accepted ideal of 5 degrees and is an indication of very low flow of refrigerant through the system.

Subcooling: with the boiling point of R22 at 67 degrees being approximately 130psi and the bottom of the condenser being 67 degrees there is no subcooling seeming to occur. This too seems to indicate very low flow through the system.

All these data points are consistent in pointing to very low the flow through the system. The question to be answered is whether this is due to low charge or a big restriction in the system. I'm in agreement with the tech and his boss that the most likely cause is a restriction due to the following logic; the liquid pressure is what is expected given the ambient temperature while the suction pressure is -2.7 when it would more commonly be expected 60psi or so.

I may have to rebuild the system anyway. A compressor that has run for a long time with low/no flow can easily get messed up internally though given the vacuum it's pulling it does seem to pump. However, there is a strange rattle that could be only due to the low flow or it could portend future failure. I've got to place a bet one way or the other. Either way this is an interesting challenge and a great distraction from the other issues in my life.

Now, I, the tech, and his boss could all be wrong. If you see blind spots in the logic I've presented I would appreciate any additional thoughts. I'm beginning to think that, given the number of systems in the coach, I should buy all the tools, get sufficient training to be certified so I can buy the refrigerant, and do my own work. Tool drool occurring NOW!

[Richard]

Jon,

The only part where I disagree with your logic and tech's input is the compressor output pressure. 130 psig is not normal in my experience, it is about 100 psi low. Can you point me to the sources which are indicating that 130 high side for R22 is normal?

Let me give you some data from my SCS system. I AM dealing with a clogged TXV valve. I replaced the compressor over the winter but that may not have been the original problem. Before the replacement surgery the system did not have ports to check pressures. So anyhoo, my pressures with a clogged TXV were 0 to -5 psig low and 300 high. Early in the diagnostic process I added refrigerant to see how the pressures would respond. Raised the low side to 30 (still low) and the high side went to 450. This is all with R 22, the same gas you are using. Real techs always replace TXVs when they replace a compressor. I learned the lesson the hard way.

I understand your point about the pump rattling because it's starved. I would still put some gas in it and see what happens as you raise the low side.

I understand about the tool drool. I went through the same route. You can get your license through taking an on line course. With your chemistry background it will be a cakewalk. Tools are going to be expensive. Oxy Actylene torch 350, vac pump 200, gauges 125, N2 setup 150, and a bottle of R22 300. Those are off the top of my head guestimates, but I post so that those who balk at AC tech charges will understand what it takes to even start working on a system.

[77newell]

Thank heaven I already have the torch. I expect the service call plus the previous call to total $400 labor and the refrigerant another $100 or so. The tools aren't that much more than that, though I'd have to buy the R22.

Here are the temperatures/pressures I found online for R22

Temp PSI
60 102
70 122
80 144
90 168
100 196
110 226
120 260
130 297
140 337
150 382

According to what I recall from my engineering days (which were long enough ago I could be all wet), the temperature in the condenser where the bulk of the vapor condenses would determine the pressure on the high pressure side of the compressor. Since we were operating at about 67 degrees ambient air temperature that aligns pretty well with the 130ish pressure I recall we had. Since there will be losses (rises in temperature as you work from outside to inside) due to the transfer coefficients between the air and the fins, between the fins and the tubes, and between the tubes and the vapor, the actual temperature inside the condensing tubes will be higher than ambient, but I would not have thought it would be on the order of 60-70 degrees. There may be other variables that I'm not taking into account, but when this thinking jived with the service manager's off-the-cuff reaction that the pressure made sense given the cool day I convinced myself I was at least in the ballpark.

Richard, it's always good to hear from you. Your expertise far exceeds my own. And besides, you have better tools.

[Richard]

I understand the impact of ambient. And I don't have readings from the Dometic system at that temp. My readings were in the 90 to 95 ambient range as best I remember.

It's easy for me to say to add a little gas and see what happens because I have the gas (Rhonda would agree) and the gauges. It's a much more expensive proposition when we are paying for a service call.

You can buy a nice set of gauges and a few small cans of R22 (ebay) for less than the service call.

[77newell]

It is probable that both our perspectives are accurate, the difference is that rate of flow through the system. The higher the rate of flow the greater the pressure needed to drive the heat exchange between the refrigerant and the air. So, in my system that is presumably plugged and therefore has zero flow, or close to it, the pressure will be determined directly from ambient temperature. In a system at full flow, it will require a higher pressure to cause the refrigerant to condense in the limited time it has in the condenser. The sizing of the capillaries is set to produce this needed pressure with the flow needed to convey the heat from inside the coach to outside the coach.

I figured this all out in the middle of last night, I had nothing else to but sleep and this was bothering me. Given that my capillaries are probably 0.054" diameter (and there are two of them) I would expect to see a fairly fast bleed down of pressure when the compressor turns off. If that happens then I will add R22, if not we need to try clearing the capillaries. I'm reluctant to add R22 myself since I have no way of recovering it if that doesn't work and I will not just vent it to the atmosphere, ergo I need the tech help.

[77newell]

All is operating normally now after lots of noodling and some investment in tools.

The tech came and we ended up recovering the R22 into a container for incineration, we weren't sure of the history or purity of what was in the system. With a gauge set attached to the system and a nitrogen bottle we pushed 340psi into the low pressure line and vented the high pressure line. We got flow through the system. When we shut the N2 off the pressure gradually reduced until it hit 40 psi and then hung up there. We tried several times and got the same result. I decided to work on it myself from this point on which I could do without violating any state or federal laws.

I bought a Goss nitrogen regulator $69, a CPS micron vacuum gauge $150, a FJC 6912 vacuum pump $121, and a yellow Jacket gauge set $95, and some Sil-Fos 15 silver solder - 2 sticks at $8. Sil-Fos 5 is considerably cheaper but harder to work with. I also rented a 40 ft tank of N2 from Airgas for $30. I already had an acetylene torch.

I removed the schrader valves on the access ports and tried blowing 300psi N2 backwards through the system, it worked as before except the pressure did not hang up at 40psi, the pressure just drifted to zero once the N2 was shut off. I then set up a gentle N2 purge of the system and unsoldered the filter drier. I blew out the system with N2 hoping that any debris left in the liquid line would be expelled. I then soldered a new filter drier in place, again with continuous N2 purge. The new one was a Emerson 052S ("05" is the cubic inches of media in the filter, "2" is the number of 1/8inches diameter of inlet and outlet, and "S" indicates the end fittings are for sweated connection. The filter drier was covered in wet rags during the soldering.

I then installed new schader valves with TFE seals, pressurized the system to 200 psi, locked that pressure in and let it sit overnight to check for pressure loss due to leaks, there was no loss. Then I pulled a vacuum down to 300 microns, again that is an indication of no leaks. I disconnected the gauge setup and left a vacuum in the system.

The tech came back this morning and put in enough R22 to give about 8 degrees superheat to the vapor returning from the evaporator to the compressor. I was surprised at how much the vapor temp varied and how long it varied before it settled. Patience is a virtue. Cool air is in the house! I doubt I'm getting the full 13,500 BTU/hr, but I'm getting sufficient.

Something additional I learned along the way. Starting in 2020 it will be illegal to import or manufacture in this country the R22 most of our systems are filled with. While R22 stocks last the price of this stuff will raise dramatically and there is no approved "drop-in" replacement for our split air conditioning systems. We can't reliably convert our systems to the currently used R410a because it operates at high enough pressures to overstress our current components, so we will have to replace the components (compressor, condenser, and evaporator) when R22 is no longer economical. On my coach I believe it will be possible to deconstruct a Dometic Brisk Air rooftop unit built since 2010 and install the components without too much work in the existing locations.

I hope my description of what I went through will be helpful to those facing similar circumstances, though my biggest hope is that you never have to face these circumstances. Then again, I acquired new skills and TOOLS.

[MrE]

Have you looked at any of the newer high efficiency climate control systems from Espar? http://www.eberspaecher-na.com/business-...oning.html

[encantotom]

the espar ones are all rooftop which doesnt help us with basement airs.

tom