Gassing and oil

[Cra$h 0veride]

When regassing a system with r290, is it necessary to pull a vacuum first or can you just flush out the system with r290 then pressurize?

At what pressure does the system need to be filled to (r290)?

And finally, when filling compressor with oil how is it possible to determine how much to put in? And where do you put it in (mineral oil)?

Thank you for your time,

Cra$h

[Stewie007]

No, you MUST, I repeat, MUST draw a vacuum before charging. You have to remove the moisture and atmosphere, otherwise it will hurt your unit's efficiency. Purging it isn't enough. That just removes the air inside. But the moisture remains.

Oiling the compressor is the first thing you do before drawing a vac. Once done you then draw the vac. I'd do it overnight, that way you're assured a pretty darn good vac. Overkill is the best way to go. Leaves nothing to chance.

When I draw a vac on a unit at work, we usually won't accept anything over 0.7 millimeters of mercury. (At least I think that's what those gauges read)

[runmc]

Drain oil through the suction or service port. They will be the larger of the three tubes coming out of the compressor. If your not sure, post a picture and they can be marked. Measure the oil you take out and put back that much. It depends on the size of the compressor as to how much oil it holds. You may have to check manufactor specs.
After a tripple evac. I would add approx 50psi of propane to the system and start it. Add r290 very slowly. Give it a squirt and let it run for 20 -30 min. You will be looking for frost to start returning to the compressor on the suction line.

Start the build and take pictures. We will help as u go. :)

[Cra$h 0veride]

I don`t have a vacuum pump so I will have to get the vacuum drawn for me by refrig techs. So your saying that I add 50 psi of propane then keep adding propane at 20-30 min intervals until I get frost on the suction line then stop at the slightest apperance of frost, can anyone verify this?

Also, I don`t know how much oil came out of my compressor and I need a way to find out how much to add and I don`t even know who makes this compressor let alone model, etc...

http://img75.exs.cx/my.php?loc=img75&image=39qs.jpg

(ignore arrows)

[runmc]

Add the propane untill the frost gets back to the compressor. You don't want the compressor frosted. A couple of inches short of the compressor is a good starting point.

Nice rotary compressor you have. I'll give you a wild estimate of 8ozs of oil.

[Cra$h 0veride]

Would length of suction line and/or a suction accumulator have an effect on the optimal pressure?

[saratoga]

Theres going to be a little bit of pressure drop if you have a long or too narrow suction line. I doubt it makes a huge difference though. Sort of like the 3/8 verses 1/2 inch tubing with watercooling, except using a compressor that developes ~1000 ft of head instead of a magdrive pump with 5 :)

[Cra$h 0veride]

So, is it better or worse for performance to have a longer suction line?

[gkiing]

charge throught the low side until it is running 2-4" hg with nothing on it. Suction line will not affect performance, unless its a really small compressor in which case it will increase the amount of refrigerant in the system. If you really want to charge it properly charge it till the temperature 6" fromt the compressor is 10degrees f higher than the corresponding temperature converted from the pressure on the lowside gauge.

[Cra$h 0veride]

I don`t seem to understand that whole 6 inches thing about knowing when it`s properly charged, could you clarify?

[Stewie007]

What he is saying, is that on the suction line 6 inches from the compressor you want your temperature to be 10 degrees F above that which you convert from your low side pressure.

Meaning if your low side pressure is 90PSI (hypothetical figure), and you convert that for temperature. Your suction line at 6 inches from your compressor will exceed that by 10 Degrees F.

[Cra$h 0veride]

How do you convert pressure into temperature, is there a formula or something?

[Stewie007]

Yeah, I don't know it myself, but you can google it.

But you might wanna rely on someone else for that, because I'm going to miss that question on the test :p

[hatemi]

You need a preasure&temperature chart of a given refrigerant to convert the prasures to temperatures.

[chilly1]

You have a P/T chart and an explanation/training manual coming in the mail.
The oil shoild reain from that hole in the side of your compressor. Measure how much comes out and only replace that. If you can't get any out and seeing it is a rotary. add 3 OZ to the suction accumulator before start up. and 3 OZ into the hole before assemble 6 oz in the < 1 hp rotary should be plenty.