Compressor problems with vendo 144

[joesquid]

Hope someone can point me in the right direction on this problem as I'm not an expert in refridgeration units.  I have a 1957 Vendo 144E with a 1/4 HP, 3.9 amp (50/60hz, 115VAC) compressor (I'm assuming it's the original unit).  When I run the compressor, the first pass and half of the second pass of the rear column of the evap ice up but the rest of the passes (including all passes in the middle and front columns) stay at room temperature.  The icing begins at the expansion valve and continues to about half way through the second pass.  From there the passes get warmer.  I'm testing the whole deck out of the machine and it didn't do this when it was in the machine.  (Pulled deck for machine restoration)
I'm assuming either low refridgerant (possible leak?) or blockage in the second pass of the evap.  As much as I want to send this off to Eric at Global Compressors for a complete restore, just can't afford the extra cost right now.  Baby #3 due September 1st....and it's a girl...Lord help me, I'm financially ruined!! (haahaa!!)
Can anyone give me some pointers on this problem and possible solutions?
Thanks

[globalcompressors]

Do you have proper air flow across the evaporator coil? How long are you letting the unit run? The coil will tend to freeze up if there is no air flow and prolonged running. Remember, the unit was fine when in the machine. It's unlikely anything happened simply by removing the unit. However, there could have been a leak created if the unit was handled rough. The coils will cool, through out, when the temperature drops in a confined area, like the box. If it freezes at the cap tube, when in the box, then you need to be concerned about low charge.

Eric

[joesquid]

Proper airflow across the evap coils was also one of my concerns.  I had wondered if removing the unit from the environment in which it was designed to run would adversely affect its operation.  I've let it run for 20 minutes with no change in the status of the coils (first two passes icing, the rest warm) and can hear the freon expanding in the expansion chamber.  At one point, the return line from the evap to the compressor started getting cold but then warmed up again.  I couldn't get the system to repeat that particular feat after several sart-run for 20 min-stop attempts.  I was also very careful during removal and transfer to the platform on which it currently resides.  Guess I'll just have to wait until I can get it back into the machine and try another optest.  Thanks, Eric, for the assistance.  Maybe I'll sweet-talk my wife out of the funds to let you overhaul/restore/convert the thing to R134a.  It's amazing what you can get the wife to agree to when she's doped up in the delivery room haaahaa!!
Thanks

[globalcompressors]

No problem. Remember, air flow, air flow, air flow! My feeling is, you can't get enough. It's so very important for both upper and lower coils. If you need anything, just ask.

Eric '>

[Jim]

Here's an idea I had seen by on of my refrigeration guys...

We placed a large cardboard box around the evaporator to simulate a cooling compartment. If my memory serves me, we used a box from a large computer monitor. We were even able to get pretty low temps for testing purposes.

With this technique, you might see if it changes the frost pattern or diminishes it enough for you think everything will function properly once back in the cabinet...

[joesquid]

Jim,
  I tried the box test over the weekend.  The air escaping the box was colder but there was no change in the frost pattern on the coils.  It starts at the inlet of the expansion chamber and ends halfway through the second pass of the rear column.  Guess it's low on refridgerant.  Can these older units be recharged?

[Jim]

Well, as Eric at Global Compressors stated, it could just be low on freon...
As far as adding freon, well, if there is no soldered fill valve, then the system will have to be broken into and have one put inline.
If there's a clamp-on valve, I recommend cutting into the system right where the hole is pierced and soldering in a valve there.
Once the system has been opened, it will need to be vaccumed down after completing all soldering; including the new dryer that should replace the original one...

[globalcompressors]

Ditto. All the "clamp on" valves are leakers. Every single one, I've seen, leak. Like Jim said, change the dryer, weld in a service valve, on the low side, and pull a good vacuum. If you can't get R12, I understand R409 is a good replacement. Ask your service man what he thinks is best.


Eric

[joesquid]

Jim/Eric,
  There's no valve in the system at all.  One line completes the circuit through through the compressor, condensor, evap, then back to the compressor.  There's another line that extends from the compressor about 4 inches and dead ends.  It looks as if it was clamped then soldered at the end.  Guess I'll have to find a service guy to do this as I'm totally out of my element now.  Are there any questions I should ask to ensure i'm getting someone that can/will do

[joesquid]

Sorry, somehow it posted while I was typing.  What I was asking is what questions should I ask to ensure I find a service guy that'll do a good job on this compressor and what's a ballpark figure for dryer replacement/freon recharge?  What is a dryer anyway?
Thanks for the help and the patience!