Refrigerant charging question

[jmeadows]

In the summer I rely heavily on superheat and sub cooling to tell me if the refrigerant charge is ok , as well as diagnose issues . I was wondering if there is a definitive way to tell whether or not the charge is good in heat mode on a heat pump. I’ve heard of using the discharge line temp and taking the outdoor temp and adding 100 to it and that should be your discharge temp.

[pageyjim]

Not that I know of. The best method I am aware of is a chart that gives you a temp rise at a given ambient temp. I don't have it handy but you can find one if you do a search here.

[ksefan]

You can also verify the sub cool is above 10 like in ac mode. If you have to top one off in the winter it is best to return in the spring and check ac mode.

[Snapperhead]

Yea ... getting it running good in winter is about all you can do , then if you have time , and it bugs you at night , go back when its 90 out

Or do like most do ... fuhgedaboudit

[EugeneTheJeep]

Yea ... getting it running good in winter is about all you can do , then if you have time , and it bugs you at night , go back when its 90 out

Or do like most do ... fuhgedaboudit

Exactly, by summer it is a new problem, the heat pump is working too good now.

[martyinlincoln]

Still check superheat and subcool to look at refrigerant flow. Check charge by measuring air flow then calculate BTU output. Every AHRI match gives BTU at 47 degrees and 17 degrees, extrapolate from there to match your outdoor temperature. Many have expanded data that gives the info in 10 degree increments.

[jmeadows]

I know this is going to sound like a really elementary question but I don’t see how you would even get subcooling if you had your low side hose attached to your true suction port and your high side hose attached to the discharge line . Your measuring a high temp discharge gas and and your true suction I get how you would get superheat in heat mode however not subcooling .

[martyinlincoln]

I know this is going to sound like a really elementary question but I don’t see how you would even get subcooling if you had your low side hose attached to your true suction port and your high side hose attached to the discharge line . Your measuring a high temp discharge gas and and your true suction I get how you would get superheat in heat mode however not subcooling .

Liquid line and true suction. Liquid line stays liquid line in both modes.

[pageyjim]

Not that I know of. The best method I am aware of is a chart that gives you a temp rise at a given ambient temp. I don't have it handy but you can find one if you do a search here.

Outside of the above you could build up the heat load inside the home and turn on the AC and charge a txv system with a charging jacket in lower outdoor temps even in the 40's or lower supposedly. I would opt in most cases to do the above and make finer adjustments in spring-summer.

[garyed]

I've tried a few different methods of charging heat pumps through the years & the one i like best is 15*(+ or -5*) suction temperature below outdoor ambient. The TD between them rises slightly on milder days & drops slightly on colder days but 15* usually gets you pretty close.

[Bazooka Joey]

Believe some manufacturers say ( matched system ) to use a certain amount of refrigerant for every feet above the initial 15’ of lineset then come back in the warmer weather to fine tune it by subcooling/superheat in cool mode.

[doc havoc]

Pretty good article here.
https://www.hvacrschool.com/checking...t-pump-winter/