[GooseBone]

Hi all, I have a feeling I may have to change a piston for a 4 ton Rheem (the nice new ones). Customer just wanted existing condensor relocated and I just peeked inside of piston compression nut and notice it was a .070-something. I'm used to seeing .082 for 4 tons (for Lennox anyway) Also noticed hi head pressure (340psi on an 80* day) Got superheat on point
So... I know the answer is probably no, but if I pumped condensor down and left 5-10 psi in the lines then would I be able to swap it on the fly? (To avoid half /hour vacuum time) Or would the POE oil suck in moisture? Anyone try it with success? Or just stick with a good ol'vacuum?
Gonna double check piston size with supply house tomorrow.

 

[Red Man]

No need to pull a vacuum in that situation.

 

[heatingman]

Ive done that for swapping schraeder cores, but I doubt you would have enough time for the piston, cause you need to oil or nylog the seats, and pulling the old piston may take a few minutes.

I would plan on pulling a vac, but you could try it and see. Just be ready to pull the vac.


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[heatingman]

No need to pull a vacuum in that situation.

Only if he is super fast and maintains positive pressure.


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[ga-hvac-tech]

Only if he is super fast and maintains positive pressure.


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If he is slick with it... he can use the pressure to 'blow' the piston out...
Be sure to put nylog on the threads and a new teflon ring in... before re-assembly.

 

[Red Man]

I guess I’m used to opening larger systems, but even on little reach ins, the oil will off gas for at least a few minutes.

 

[HVAC_Marc]

Does this qualify as "de minimus"?

 

[beenthere]

340 on an 80° day is not out of line. Varying with indoor load.

 

[Core_d]

Before you even try it ide call a distributor and see the outdoor unit actually takes. Different brands use slightly different sizes. Depending on the efficiency of the unit 340 might not be so far out of line. High indoor load can raise it some too as stated and 4-5 ton units will typically run a higher head pressure than the same smaller unit.


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[GooseBone]

Checked with supply house and it has correct piston size in there.
Thanks all for input and good to know it can be done if I run into that situation.