[77newell]

I have 3 separate split A/C systems on my 93 coach. It appears the one with the evaporator near the entry door has failed. The local service tech has determined the existence of a stoppage somewhere between the fill valve just downstream of the condenser and inlet to the compressor - he is guessing it's in the evaporator, but it's just a guess.

My question is: does anyone know the BTU capacity of these units? And has anyone any experience redoing a failed one, and if so, could you provide the details of what was done and what the parts source was?

[Fulltiming]

If it is the same as my 1992, they are Dometic units and are 13,500 BTU each.

[Dmatz]

Sounds like the thermal expansion valve has failed. It is has a filter dryer it could be plugged as well. It's a refrigeration system a "plugged" line and or component is not logical. How is your confidence in the diagnosis?

[77newell]

The filter/dryer is prior to the pressure measurements so I doubt it is the problem.

The system I have does not seem to have a "thermal expansion valve", but has two capillary size tubes feeding the evaporator. It could be easy for those to plug. If they are plugged they must be completely plugged as there is no cool spot detected anywhere in them which would be the case if there was only a restriction.

I'm still researching and confirming the diagnosis, but what I've determined so far confirms a plug somewhere downstream of the compressor, condenser, and dryer and prior to the compressor low pressure side. I still have lots to learn.

At the moment, I'm thinking of deconstructing a roof air conditioner for the necessary parts since they are designed for 13,500 btu's which is what my system seems to be.

[bestgenman]

Jon, an 89 model  that I once owned, had four split systems and you are correct about the cap tube expansion design.  One  of the evaporators plugged at the cap tubes.  I cut them out and replaced with an expansion valve.  My local refrigeration supply helped size the valve as I had no idea how to proceed.  It was a lot of work but performed perfectly.  I may still have the info if you are interested. 


I did learn that silver solder is not needed and was glad about that since the inside of the copper tube will flake unless an inert gas is inside the tube.  That flaking will plug the new cap tubes.  I used a solder that works well with a propane torch and no flux, your local refrigeration supply house can tell you which silver content to use.


The condensing units do not do a good job of moving air since they are "couped up" in the side boxes.  your idea of using a roof top for parts is perfect!  The problem with the evaporator is the size may not fit your space.  


I built two condensing units from roof tops, here is the design:  Using the squirrel cage blower that was for the evap,  it now becomes the fan for the condenser .  Swap the condenser  coil to the evaporator location so the fan blows  the heat down through the bottom of the coach box, leave the compressor in position and re-solder to the cond coil.  Cut off the motor shaft that drove the propeller fan since you won't need it.  the efficiency increase is dramatic.  The electrics stay in place as does the fan, compressor, & base of the roof top (you do have to cut it down to size to fit into your coach box).


I do have several parts left over from that project so let me know if you're in need of something and I'll check the stash. 

[HoosierDaddy]

There are several RV salvage places in the Elkhart , Indiana area that have had roof A/C units. The last time I checked they could be purchased for as little as $250. They will be bent or maybe had been mounted and removed because they were caught on an overhead door and damaged.

[Richard]

Jon, Do you mind posting the gauge readings?

[77newell]

Gordon: thanks, it's good to know the concept works. These systems are pretty simple in configuration, it seems mostly a matter of figuring out how to fit the parts into the space available.

Hey Richard: hope all is well with you and Rhonda.

Suction side was approx. -1.7psi, high pressure side was +130psi approximately.

[Richard]

I am no AC expert, but those numbers suggest low gas, not stopped up capillary tubes. Stopped up tubes in my opinion would give you numbers such as 0 to 20 on the low side and above 300 on the high side. Airplane guy has the notebook for my old 390 where I recorded operating pressures for the Dometic system. To the best of my memory they were in the range of 60 on the low and 250 on the high at 90 degrees ambient, but don't take those numbers to the bank.

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I am no AC expert, but those numbers suggest low gas, not stopped up capillary tubes. Stopped up tubes in my opinion would give you numbers such as 0 to 20 on the low side and above 300 on the high side. Airplane guy has the notebook for my old 390 where I recorded operating pressures for the Dometic system. To the best of my memory they were in the range of 60 on the low and 250 on the high at 90 degrees ambient, but don't take those numbers to the bank.

[bestgenman]

Richard is spot on with those readings.  60psi would be 34 degree evap temp and 250 psi around 118 degree cond.

I agree the pressures are too low indicating not enough gas.  If you charge to 60 psi suction and your high side goes up towards 300 then your cap tubes are suspect.  300 is too high, watch your compressor current too.  I don't recall your ambient temperature but it does play a part in these readings.

If you have a leak it is most likely around an oily area.