blast chillers

[85goldwing]

How does a system with a receiver get air bubbles going by the sight glass down stream of the receiver. Maybe a dumb question, but I thought that condensed high pressure liquid went in to the receiver on the bottom and liquid refrigerant was taken from the mid point of the receiver. Thus ensuring the high pressure liquid stayed liquid up to the txv where it changes state to a low pressure liquid. Ok so now beat me up on this but teach this old dog a thing or two in the process.

[jpsmith1cm]

You are correct in your description of how a receiver works (well, except for the part where it draws liquid from the mid-point. It actually draws from very near the bottom where the liquid sits.)

You've answered your own question and don't quite know it yet.

If there are bubbles in the sightglass, the most common problem would be that you do not have enough gas.

[85goldwing]

This unit for sure was not short on refrigerant. I took out just short of 4 lbs on a system that calls for 3.3 lbs of 404a. So I am still wondering about the air in the sight glass. Could a over-sized filter/drier produce these bubbles in the sight glass?

[klove]

This unit for sure was not short on refrigerant. I took out just short of 4 lbs on a system that calls for 3.3 lbs of 404a. So I am still wondering about the air in the sight glass. Could a over-sized filter/drier produce these bubbles in the sight glass?

You don't have "air" in the sight glass - what you're seeing is refrigerant in a vapor state. You have to remember that refrigerant coming out of a receiver is not subcooled, it's saturated (unless you want to get into some very heavy theory about refrigerant dynamics). Thus, if you have anything that throws the heat balance off in the system, e.g.; non-condensables, dirty condenser, recirculated air on the condenser, etc, it may create the condition that you describe. A restricted filter/drier of any size can and will create what you're seeing.

[jpsmith1cm]

You installed an oversized filter drier.

This modified the actual system charge. It would depend on how much you oversized the drier how much additional refrigerant it would require to clear the glass.

[ivandykeman]

When did you take your superheat reading? Was it close to or at design temperature?

[85goldwing]

Tomorrow I will put in a new filter/drier. I'll check for leaks with nitrogen. Then I will pull vacuum, check for leaks again and then pull another vacuum using my jb micron gauge. If all goes well, I will just have to play with the txv to get the super heat right. I'll post results tomorrow or the next day.

[85goldwing]

I did add additional refrigerent to compensate for the oversizing of the new filter/dryer. To answer ivan, I never did reach anything close to desigh temp.

[85goldwing]

got the unit running today. Added the correct amount of refrigerant via digital scale, adding the correct additional amount for the over-sized filter/drier. It only got the temp down to 37 degrees. Still have some bubbles going by in the sight glass, but not as bad. I have started to adjust the new txv, slowly to see the change. Super heat is only 3.5 degrees. High side was 210 PSIG at startup, suction side at 70PSIG at startup. After running for about 45 minutes it was at 190PSIG high side and 75PSIG suction side. I didn't get amp load reading, but will first thing in the morning. I am hoping to get some good feed back from you guys. Thanks in advance

[jpsmith1cm]

You've got a 70 pound suction pressure with 404a.

THERE'S your problem.

[85goldwing]

Then plot thickens. I got in touch with the factory rep. to confirm some information. Turns out the tecumseh compressor that got shipped is made in France. The part number that was ordered was correct, but the wrong was shipped. They are sending another compressor under warranty, but the labor and materials will be a total loss. I will keep the board posted as the progress goes. Thanks for everyone's help and thoughts and feedback.