View Full Version : Mcquay Duals
05-18-2004, 10:38 PM
Hi there this is my first post
I am wondering if anyone can give me a process to ensure my charge is correct as i have add refrigerant to a mcquay chiller Thanks sorry if its a dumb question
05-19-2004, 06:57 AM
What refrigerant? Whats the discharge superheat at full load? LL subcooling? Suc superheat? Condenser/evaporater approach?
05-19-2004, 04:56 PM
I relize that ther should be 12-18oF superheat discharge or 1 of superheat on the suction
What should the subcooling be
Sightglass clear or bubbles etc
I think McQuay still recommends 14-16 degrees discharge SH at full load. This must be with liquid injection turned off and the unit not oil logged. Forget what the suction SH is. I've seen what would calculate to a -3 degree suction SH and good dischage SH due to where readings are taken. What size dual and how the reading is obtained is a factor. What panel is on the unit 100, 200, or MTII? The shop order will give the design approach temps, SH, and subcooling information. Typially if it is a newer unit subcooling will be about 8-9 degrees at full load. At that point depending on the condenser design the sight glass may or may not be clear(to have 8 degrees SC one would think the glass must be clear). I've seen units that will never clear the main liquid line sight glass when charged correctly. Does this unit have a condenser sight glass with a ball in it? If so the level would typically be at the top or slightly above the sight glass at full load. This should get you in the ball park.
Make sure you get good reading use insturments that are accurate and reliable. Don't just trust the microtech readings. Trust with verification.
Need to add that the 8-9 degree subcooling is typical of two pass condenser with a 9-10 degree delta T on the water. Tube fouling at design conditions.
12-03-2004, 12:26 AM
Subcooling will typically track condenser delta T with a clean condenser. Charge should be checked at design conditions, that is usually ARI 44 leaving evap and 85 entering cond.
12-04-2004, 09:02 PM
P.S. that's about all I know.
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