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Lennox uses the approach method in conjunction with subcooling for charging. Their approach temperatures are below 10 degrees. Check the installation instructions for Lennox AC units.
Originally Posted by hewitt With103 outside system seems to be okay.Remember design conditions are 95 od 75 id with 50% humidity There are so many standards for different purposes it's difficult to keep them straight. The rated capacity of a condensing unit is from these conditions. Cooling Standard: 80°F (27°C) db 67°F (19°C) wb indoor entering air temperature and 95°F (35°C) db air entering outdoor unit. I cut and pasted that to make sure I got it right. Design conditions (Manual J) depend upon the location and local codes. Maybe that's what you were referring to? Yep, they don't tend to keep up when design conditions are exceeded, unless they're over-sized like mine. It stays 75° in my house even when it's 110° out. In my book it's sized just about right, and it wasn't by accident either.
With103 outside system seems to be okay.Remember design conditions are 95 od 75 id with 50% humidity
Originally Posted by daviddsims I was a little worried with the amp draw at 12.5 and still getting into the hottest part of the day. The FLA was 14.4 The amp draw could be normal. The compressor in the pdf file below has an RLA of 14.4. It may not be the compressor in your unit, but yours should have a similar amp draw profile. The RLA is for sizing the circuit/protectors feeding the unit, and isn't equivalent in function to the FLA of a fan motor. Compressors are actively cooled by returning refrigerant and can run all day long at higher than RLA. A fan motor OTOH, will generally trip out on thermal overload if it runs very long at higher than FLA. BTW, looks like the high suction pressure isn't really high in this case. There's a huge difference between a cap tube system and a high efficiency TXV system.
Originally Posted by daviddsims SP=82 DP=255 SL temp=65 LL temp=110 Still not completely happy with the results. Those numbers look pretty good if it was 103 outside. If your TD across the evaporator was 15 or so you may be O.K. depending on the inside coinditions. What about your indoor DB & WB?
I was a little worried with the amp draw at 12.5 and still getting into the hottest part of the day. The FLA was 14.4
The outdoor unit has superheat charging chart so I used my Fieldpiece HG3 to get a 12 target subcool. Tell me about LL temp - outdoor rule you referenced?
Originally Posted by daviddsims So what is the consensus on this unit? Even adding refrigerant having trouble getting to the 10 degree subcooling on this unit? What is the LL approach temperature? Liquid Line temperature - Ambient temperature if it is pushing 10 degrees may be a dirty condenser coil. If coil is clean it may be non condensables.
Originally Posted by daviddsims So what is the consensus on this unit? Even adding refrigerant having trouble getting to the 10 degree subcooling on this unit? You didn't add enough.
So what is the consensus on this unit? Even adding refrigerant having trouble getting to the 10 degree subcooling on this unit?
Get in the habit of measuring SL and LL temperatures at condensing unit and at evaporator. It will reveal lineset problems.
Yeah I should have taken it at the evap as it does run through the attic and it is 103 here as well.
Originally Posted by dijit Superheat at the outdoor unit really doesn't tell you much. You should measure it as close to the evaporator as possible. Yep, there's quite a difference on mine. About a 6° rise in line temp from evap to compressor. Figuring in pressure drop that gives me about a 7° difference in SH. It's about 103° outside right now and my line set runs through the attic.
Originally Posted by daviddsims No it is not a heat pump. I measured superheat at the outdoor unit and subcooling at the outdoor unit. Superheat at the outdoor unit really doesn't tell you much. You should measure it as close to the evaporator as possible.
No it is not a heat pump. I measured superheat at the outdoor unit and subcooling at the outdoor unit.
Is this a heat pump? If so, measure the rise in temp of the lines across the reversing valve to make sure it is not leaking. Where are you measuring the suction line temp? is this as close to the evap as possible. and measuring LL as close to condenser as possible?
8SC. Dirty coil maybe.
SP=82 DP=255 SL temp=65 LL temp=110 Still not completely happy with the results.
Originally Posted by daviddsims Took another look today and sure enough it had a txv on the evaporator. I added a small amount of refrigerant to try and get to 10 degrees subcooling. Getting about a 15 degree split out of the evaporator. What are you readings now.
Took another look today and sure enough it had a txv on the evaporator. I added a small amount of refrigerant to try and get to 10 degrees subcooling. Getting about a 15 degree split out of the evaporator.
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