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Recharging Roof Air

June 26, 2011, 09:17:12 am

We are leaving next week for St. Louis/Memphis/Nashville.  Temps expected in the upper 90's.  When we purchased our coach in the winter of 09, I obviously was not diligent enough in my inspection procedure, in that the first time we incurred hot weather, the center a/c was not working.  I was at the factory and they said the unit had to be replaced for an arm and a leg.  These are 15,000 btu dometic a/c heat pumps.  Upon inspection yesterday, I could feel the compressor start  but obviously, the system was out of freon.  Purchase from an a/c supply store a 3in long 1/4 in diameter copper tube with a schrader valve attached.  I drilled a 3/16ths hole in a horizontal low side line adjacent to compressor, rheamed it with a  pair of long-nose pliers to facilitate a tight fit on the tube, and silver-sodered in place.  A friend of mine who owns an a/c store let me use a micron vacuum gauge which is t'd into the gauge line.He said if you can achieve and hold for 5 minutes a reading greater than 550, the leak is minute.  After 5 minutes on the vacuum pump, I achieved a reading of 975, and after 5 minutes of rest, it dropped to 825.  Charged with the appropriate amount of R-22 (20.5 oz) the system works perfectly.It seems must more cost effective to me, even if I have to charge this unit annually, to approach the problem this way rather than replace an expensive unit and endure the labor of replacement.

Gregory S
2003 Designer

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Re: Recharging Roof Air

Reply #1 – June 26, 2011, 09:34:43 am

Very smart approach to a "problem."  A photo of that new valve would be really helpful to those of us not conversant with air conditioners.  It sounds like the kind of repair that even I could make.

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Re: Recharging Roof Air

Reply #2 – June 26, 2011, 09:46:05 am

You know, for the $ saved from this fix you could buy a complete set of ac tools including gauges, oxy acetylene torch, silver solder and still be money ahead.  One of my units has a noisy compressor start up, I'm going to amp it and probably put in a hard start kit to give the comp. some boost.  Nice job GregoryS.

Chuck

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Re: Recharging Roof Air

Reply #3 – June 26, 2011, 09:50:54 am

George, as per your request, I love it when I save big money.

Any suggestions for fun things to do -  Memphis/Nashville?  Now that I have saved so much money, I am going to spend some.

Gregory S
2003 Designer

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Re: Recharging Roof Air

Reply #4 – June 26, 2011, 10:15:36 am

Gregory,

Thank you.  Am I correct in assuming that you used a torch and not a soldering iron?  If so and when I need to do this I get to buy a new tool. 

Whenever I have done a repair I have never hesitated to buy a new tool.  I figured the money I was saving more than paid for the tool with plenty left over for something else.

P.S.  I just boosted your Karma score 100%.

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Re: Recharging Roof Air

Reply #5 – June 26, 2011, 10:30:40 am

George,  for this application the oxygen acetylene torch is the weapon of choice.

Gregory S
2003 Designer

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Re: Recharging Roof Air

Reply #6 – June 26, 2011, 10:35:59 am

Looks like I'd have to visit good friend Gary O to get this done.

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Re: Recharging Roof Air

Reply #7 – June 26, 2011, 10:38:45 am

Gregory S,

I am not an AC technician, but I understand the principles of refrigeration.  If your roof air was low on freon it has a leak, most likely in the condenser or evaporator.  It may be very small, but it is still a leak and may increase.  As it leaks out the unit becomes less efficient.  All the tubing in a roof air unit is metal.  Dash air has rubber hoses and the refrigerant can migrate through the rubber at a very slow rate, so dash air needs to be recharged from time to time.  Same principle as air molecules in tires migrating through the rubber.  Electronic leak detectors exist that are sensitive enough to detect which side of a tube has the leak.  They are expensive, $300 and up.  If the leak is in a copper tube, you might be able to silver solder it, if it is aluminum tubing some other method would be required.  Rather hard to fix an evaporator or condenser leak, they usually get replaced, and in many cases the whole unit is replaced due to the labor cost involved of replacing a part.  However your labor is free so replacing a part may be cost effective.  New units cannot use R-22 after 2009 and R-22 cannot be manufactured after 2019.  Recovered R-22 can be used after 2019.  AC shops are required by law to fix any leaks before putting a unit back into service.

Absorber type refrigerators primarily use ammonia as the refrigerant (hydrogen is also present). Ammonia attacks copper so steel tubing is used in these units.   

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Re: Recharging Roof Air

Reply #8 – June 26, 2011, 10:39:30 am

If you have to recharge it again next year, put a dye in there. It could be in an area that is easily repairable - or a part that could be replaced...

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Reply #9 – June 26, 2011, 03:04:19 pm

For those that don't have a torch and are in a bind get a Bullet Piercing Valve, Supco's is one brand and there are others all you need is a allen wrench to install cost is about 5 dollars are less. Not as good as a soldered valve but will work.

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