Troubleshooting help please

[AzRob]

I use to work on A/C's a few years back and have had some exposure to refrigeration units but this one is beyond me abit. The unit I have questions about is a modified refrigerated semi trailer using 401a. Unit was not cooling enough, by the time I got there it was putting out 75 degree air. Unit has been working good for several years, its not something recently put together.

Here is what I observed/collected:

1. Cond and evap coils are clear, fans working.
2. 75 degree output air temp.
3. Low side pressure of 50psi and high side of 200 psi (401a) with ambient of 110 degrees.
4. The compressor and discharge line are extremely hot. One cant touch either but for a second without getting burned. (I got a good burn when removing access nut at gauge port) Was told it has been running hot for awhile now... a few months.
5. Suction line at compressor slightly below ambient temp. Also noted compressor oil glass half full and with a milky looking oil as well as running pretty noisy.
6. Appears to be a leak as oil is present on the ground under the unit. (unit hangs from bottom of trailer)
7. Unit is 3phase, evap fan motor running in proper direction.
8. 45 days ago evap motor was replaced. Unit has been cooling fine since then.

I need some advice on how to pursue this. Sure would appreciate some input into this problem. Its a small food bank that cant afford high repair bills and this one is a no charge call. Getting more info might be tough as power line to unit was rerouted to run a substitute trailer.

[powell]

I use to work on A/C's a few years back and have had some exposure to refrigeration units but this one is beyond me abit. The unit I have questions about is a modified refrigerated semi trailer using 401a. Unit was not cooling enough, by the time I got there it was putting out 75 degree air. Unit has been working good for several years, its not something recently put together.

Here is what I observed/collected:

1. Cond and evap coils are clear, fans working.
2. 75 degree output air temp.
3. Low side pressure of 50psi and high side of 200 psi (401a) with ambient of 110 degrees.
4. The compressor and discharge line are extremely hot. One cant touch either but for a second without getting burned. (I got a good burn when removing access nut at gauge port) Was told it has been running hot for awhile now... a few months.
5. Suction line at compressor slightly below ambient temp. Also noted compressor oil glass half full and with a milky looking oil as well as running pretty noisy.
6. Appears to be a leak as oil is present on the ground under the unit. (unit hangs from bottom of trailer)
7. Unit is 3phase, evap fan motor running in proper direction.
8. 45 days ago evap motor was replaced. Unit has been cooling fine since then.

I need some advice on how to pursue this. Sure would appreciate some input into this problem. Its a small food bank that cant afford high repair bills and this one is a no charge call. Getting more info might be tough as power line to unit was rerouted to run a substitute trailer.

What is the model of the compressor? Sounds like you have a semi-hermetic being it has a oil sight glass. I would suspect a busted valve.

If it's a semi, pull the head and check the valves. The customer might get lucky with a valve plate change only.

[AzRob]

Thanks. I dont have the model number handy but yes its a semi-hermetic.

I think I understand what your proposing. Valves on the way out or bad valves compromise the ability of gas to cool the compressor. Would weak valves allow the box to cool down but not cool the compressor? (The box had been cooling but compressor running hot & noisy last couple months) Also is the milky appearance of the oil caused by being too hot?

[LRAC]

1st things 1st before removing heads on compressor perform a pumpdown test, fit gauges to suction service valve and front seat the valve. This should enable the compressor to enter a vacuum reading on the gauges (you may need to short out LP temporary) should you not get a vacuum reading then start stripping the compressor head/s down.

Sorry forgot to say after the unit pumps down if it does, leave the compressor idle and see if the suction pressure rises back up, this will also indicate valve problems.

Good luck
Lrac

[AzRob]

Thanks Lrac. One question comes to mind. How do I know the suction service valve is good, that it will close all the way to pump down?
After valve is closed and assuming unit pumps down a rise in suction pressure in what amount of time would indicate a valve problem? Within a few minutes?

Thanks

[AzRob]

Finally had an opportunity to check this unit some more. Installed gauges and found unit empty. Pulled head and valve plate and found the following:





It would appear one intake valve was not installed properly from day one as I dont see how the reed valve could have jumped off the pins. That valve is wedged against the head and does not move. Can anyone identify from the pictures what might have been causing the top end noise?
Discharge reeds are of different "strength" as some are stiff to move and others open very easily.
Any input appreciated. Thanks.

[tony--1]

the reed that is not on proply is the suction reed.that wud giv you a high suction pressure.

put it together and see if it runs any better