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pende_tim
Premium Member
join:2004-01-04
Selbyville, DE

pende_tim to Tex

Premium Member

to Tex

Re: [HVAC] Goodman 2 Stage HP Defrost

Thanks, Tex.
Sure is hard to find a good tech, that is why I usually end up doing a lot of stuff myself. However when it comes to HVAC, I do not have the experience or tools. Maybe since I am retired, this could be an excuse to go back to school? ( Just kidding ).

Since the measurement was done when the unit was on high speed, it looks like we were 3* too low on the subcooling to reach your 10* target.

Now to get into a little theory: how much of an impact does this 3* make on Heating performance as far as efficiency and Delta T? How much of an impact will this make on Cooling performance?

....And to get a feel for how "short" the charge may be, the unit shipped with 188oz of R410a for 15' of line set? Any ideal how many oz are required per foot of additionaal line set? If I recall correctly the installer did not add any R410a to the system when it was installed. I have not measured the line set length, but it is pretty close to 15'.

Thanks Tim

F100
join:2013-01-15
Durham, NC
Alcatel-Lucent G-010G-A
(Software) pfSense
Pace 5268AC

F100

Member

pende_tim, I didn't see this mentioned in this post but from what I understand R410a isn't as easy to recharge. It is a blend of refrigerants not a compound like R22. So if it is low, or leaking, the mix in the blend of the R410a that is left is not the same since the refrigerants that make up the mix bleed off at different rates which changes the composition of what is left in the system. That makes it hard to just top off like the old R22 that I have. You have to pull all the puron (brand name) and replace with new to do it correctly. You can't fix the blend by adding more puron.

When R22 leaks, it is still R22 in the system. You can add more R22 and the mix is the same. The R22 freon acts more like water. You can change it's state but it is always water, event when it evaporates or escapes the system. R410a is like a mixed drink, some parts settle out at different places. Some float on top, some sink to the bottom, some in between. If it's sealed inside the system , the mix is fine. Let some out and one part of the mix escapes while the rest stays.

Tex and others seem to know better than I but R410a seems to be more sensitive to the amount of charge in the system to operate best. I don't know if it's the higher pressures or what.

pende_tim
Premium Member
join:2004-01-04
Selbyville, DE

pende_tim

Premium Member

I suspect the system was never fully charged from the get go, no leaks AFAIK.

Yes I do appreciate that R410a needs to be charged as a liquid, not vapor to make sure the blend is proper.

Tex
Dave's not here
Premium Member
join:2012-10-20

Tex to pende_tim

Premium Member

to pende_tim
Too low or too high subcooling affects both cooling and heating efficiency. Keep in mind, many manufacturers will allow ± 2-3°F when taking readings. Most importantly, when taking temperature and pressure readings, having accurate instruments is critical. Otherwise, the readings are useless. Using today's advanced digital manifold gauges (Testo, MasterCool, Fieldpiece, Yellow Jacket, etc.) are the most reliable and accurate method for measuring superheat and subcooling.

I would not get too caught up with the line set length, unless the line set is unusually long (80' or longer). In your case, charging the system using subcooling is perfectly acceptable.

pende_tim
Premium Member
join:2004-01-04
Selbyville, DE

pende_tim

Premium Member

Thanks, Tex.

So from your experience, how much of an impact would having 7* subcooling on High speed, where the manufacturer's spec calls for 8-10*?

This is assuming the readings were 100% accurate: he read the gauges correctly, they were calibrated and the digital clamp on thermometer was recording the true gas temperature, etc? As you point out there will be some inaccuracies in the measurements, but lets call it an ideal world for discussion.

I am just trying to get a feel for how sensitive performance is VS subcooling and I appreciate there is probably not a big performance hit. Just curious .