JB/Keith Air Conditioner Project

Home 2024 Forums Opening Section Maintenance Issues JB/Keith Air Conditioner Project

Viewing 12 posts - 1 through 12 (of 12 total)
  • Author
  • #85208

    I just purchased a JB/Keith system on ebay that came off a 421B just like mine. It has already been converted to R134a. Does anyone familiar with these systems have any advice on what to check or overhaul before having it installed in my plane? It has all the documents that were found in the logs but I’m not sure if it includes the installation manual. Does anyone have a copy of this that they can send me? I’m really looking forward to having A/C in this Texas heat. 🙂

    Thanks in advance!


    The receiver dryer should be replaced prior to install. the lines flushed, then to the extent possible it should be leak checked on the bench. I would blow out all of the oil and drain/flush the compressor of oil too. Then, add oil and freon per weight not pressure. What condition was it stored? are the fittings sealed? When you look in a fitting is it shiny or black in the tubing?

    Do you need a 337 or ?. Even with the manual, I would try and find a shop that has done these before.

    You should borrow a big GPU for ground testing too.


      I find it hard to even come up with a labor bill for this install so say nothing of the paper work that will be needed. Without Keith’s blessing, you may be in for some fancy FAA dancing. Hopefully you have a friendly FSDO near you. If it were me, I would do the install and then charge the system with 160 PSI of nitrogen and do a leak check on each fitting of which there may be near 100. If it holds 160 PSI for 15 minutes, then you are probably good to go. Let the nitrogen out and vacuum the system for 10 minutes and fill with oil and R134. And I thought changing both windshields was hard!


      http://www.keithproducts.com/ hmm.. no 421 manual shown on their publications page


        The installation manual that I have is for a 340 – I am not sure whether you can pick that up on the Keith site or not; if not send a PM with your e-mail address and I will send a copy to you.



        Thanks for all the replies.

        This unit was just taken out of a 421B that had a nose gear collapse and now being parted out. They just took it out last week and posted it on eBay last Friday, I purchased on Monday and it is being shipped now. They only wanted $1100 for the whole system so I couldn’t pass up the chance to at least try it and see if I can get it running. I figured even with overhauling parts and replacing parts that the total cost would be way under the 23k list price of a new system. The wife isn’t very excited about dropping 30k on a new unit. 😮


        My plan was to first take everything apart and clean it up. Then I was going to get the system flushed out and do the suggested nitrogen leak test. Once everything looks good, will charge it up on the bench and run the whole system to ensure everything looks good and functions properly. There is a shop in Austin than can do compressor overhauls in the event that it needs some work. Is there a good way to test the motor to see what kind of shape it is in? Are there any other components besides the compressor and motor that could be overhauled?



          Chris, the compressor motor, evap fans and condenser fan all have an amperage rating on the data plate or should. When you run the system on the bench, check each motor to see if it is pulling the correct amps. If any are pulling more then advertised, you will have problem down the road in no time. This means the brushes and armature need work or replacement. You will need to retest for leaks after you install the system in the plane as you will need to break lots of connections. Good luck.


          You might contact Keith and ask if they provide overhaul service for the components. Then knowing that, it might provide you with a path to obtaining the STC, following their conditions (If their STC is issued per N number) I did this with a set of used tip tanks from Metco on one of my Aztecs. Their conditions were that I used new fuel lines, bought new check valves and verified the connections on the tanks were in good condition. It worked well for both of us, I got the factory new parts that were prone to wear/replacement/age issues, they got a little cash they other wise wouldn’t, and I also did the project for about 1/2 of normal new cost.

          Either way, you might gain some valuable info by talking with them.


          Jim – I have a call into Keith to see what they can do and what kind of overhaul service they have on various parts.

          Big thanks to Geoff for sending over his install diagrams.

          Does anyone have them for the 421? The 340 version that Geoff sent is helpful but doesn’t have the dual evaporator setup like I have.


            the 340 has dual evaps, but just in a different place.


            This is similar to though not identical to the system I just overhauled in my T310. Mine was factory so paperwork was not an issue, but getting information on it was hard. Keith engineering was very helpful even though it was not their system – suggested refrigerant and oil levels. Basically they said 1.5 to 2.0 pounds of refrigerant and up about 12 oz of oil though for your system I’m sure they will be more precise given they made it. Looks like your system has a modern rotary compressor as opposed to the piston one mine uses – they are supposed to leak less.

            Good luck getting going – although it’s just a flood system it does take the edge off on hot days.


            I had a Meggit/Keith air conditioner installed (flood cooling, system sits on the “hat shelf” in rear of aircraft) in my 1980 T310R a couple of years ago by DFW Aero Mechanix at Addison Airport (KADS) in Dallas. The labor was estimated at 100-120 hours for the install, they had to cut 2-holes in the fuselage for the AC system intake/exhaust, and the system requires 100 amp alternators. It was much more involved that I initially thought. Meggit is right across the ramp from this shop, so support wasn’t far away. The facility has installed over 100 of these systems and did a great job on the install. Hope this sheds a little light on what you can expect.

          Viewing 12 posts - 1 through 12 (of 12 total)
          • You must be logged in to reply to this topic.