Fixed orifice woes

[Stiff Nipples]

i am working on a split unit installed to cool a computer server room. the Condensing unit was installed new but the fan coil in the ceiling was existing. The fan coil is a 2 ton and the condensing unit is is designed for 20000 btu's at 20 to 55 degrees F. Showed up to do a regular maint. check on the unit and found the sight glass flashing. Fixed orifice system with a headmaster valve for low ambient conditions.

***Head press 225psi and suction 70psi. No superheat no sub cooling.

I charged in 3lb 6oz of gas with out clearing the sight glass before I realized that probably wasn't the problem.

***Head pressure 275 psi suction 75 psi no sub cooling, no superheat.

I am thinking that the orifice is oversized. Any thoughts I'm gonna check the orifice tomorrow. i was also thinking about the headmaster valve but I can't think of how if it failed it would give me the readings above..."no superheat"

Intelligent Opinions Will Be Gratefully Accepted Thank You! :)

[lowcool]

the million dollar question for today is,wait for it,wait for it,

tadah
what refrigerant?

[Brian_UK]

You say -no superheat and no sub-cooling.

Do youmean that the readings were at zero or that you did not record the results?

[Stiff Nipples]

The refrigerant is R-22. No I took readings you read that correct no superheat and no subcooling temperatures. Not something you see together.....ever. I checked the orifice today and it is the right one for that unit. Question about that though. Is the piston supposed to sit loose inside the piston coupling or should there be some sort of spring or clip to hold it in place cause it slides around inside the coupling when you shake it? I was planning on installing a TXV in the unit Friday. Another question the cond. unit has a receiver on it and a headmaster valve for low ambient. Fixed orifices are a critical charge metering device would this affect my system some how?

[Stiff Nipples]

I was talking with another mechanic today. His thought on it are that the issue is with overcharge and that you rarely see a full sight glass on a fixed orifice system as the valve is always feeding. Hence the no sub cooling and no superheat.

[tonyhavcr]

You said - i am working on a split unit installed to cool a computer server room. the Condensing unit was installed new but the fan coil in the ceiling was existing. The fan coil is a 2 found the sight glass flashing. Fixed orifice system then said - it has a headmaster valve for low ambient conditions. )
receiver on it . Fixed orifices are a critical charge metering device would this affect my system some how?
Well now here's the rub Fixed orifices are a critical charge metering device
so it can not work right the new condenser was not match to the a/h

then you said I was talking with another mechanic today. His thought on it are that the issue is with overcharge and that you rarely see a full sight glass on a fixed orifice system as the valve is always feeding. Hence the no sub cooling and no superheat.

You should not see a sight glass on a fixed orifice system .

you may wish to check out the Fundamentals Forum Gary has some good stuff there

[chemi-cool]

You should install a TEV.
If the outdoor unit is under-size, you must be able to adjust the TEV so you get super heat and sub cooling.

[udarrell]

i am working on a split unit installed to cool a computer server room. the Condensing unit was installed new but the fan coil in the ceiling was existing. The fan coil is a 2 ton and the condensing unit is is designed for 20000 btu's at 20 to 55 degrees F. Showed up to do a regular maint. check on the unit and found the sight glass flashing. Fixed orifice system with a headmaster valve for low ambient conditions.

***Head press 225psi and suction 70psi. No superheat no sub cooling.

I charged in 3lb 6oz of gas with out clearing the sight glass before I realized that probably wasn't the problem.

***Head pressure 275 psi suction 75 psi no sub cooling, no superheat.

I am thinking that the orifice is oversized. Any thoughts I'm gonna check the orifice tomorrow. i was also thinking about the headmaster valve but I can't think of how if it failed it would give me the readings above..."no superheat"

Intelligent Opinions Will Be Gratefully Accepted Thank You! :)

If a piston type orifice, it could be held off its seat.

Since the cooling coil is a larger tonnage it may have too large an orifice.:) - udarrell

[Stiff Nipples]

I plan to install a TXV as soon as the approval is there. Have any of you guys seen an piston type orifice used with a condensing unit that has a receiver and and a headmaster valve. I have only seen them on a standard rooftop or residential. With those piston type orifices when I shook the piston coupling before I reinstalled it and there is definitely up and down movement of the orifice inside is there supposed to be some sort of clip to hold it in place internally? Is the coupling position sensitive as it is mounted on the vertical with the liquid line entering the bottom and of course...the top going to the distributor. Thanks for all the posts so far and the link which I...will...use...right....now! :)