The system requires more refrigerant in cooling than in heating thats the reason for the accumulator.
AND i thought the accumulator was to keep liquid from entering the compressor. Pretty sure that the charge level should be the same in heat or cool mode... and please if i am wrong someone plz let me know
You are wrong....for some cases.
But it is a charge compensator that makes up the difference, not the accumulator. The accumulator is mainly for the purpose you stated.
Heat pump can be charged in the heating mode using SC & SH. However, if the charge is adjusted in the heating mode, you will need to fine tune it in the cooling mode when spring hits. The system requires more refrigerant in cooling than in heating thats the reason for the accumulator. It's always better to charge with warm OAT and in cooling mode. I would probably go with the weigh in method, keeping in mind length of line set. In either case, charging in heat mode will get you close enough in cooling mode that you should be able to get back in spring to fine tune. (when I hook up to heat pump I always use the liquid line on high side gauge and my low side gauge to the true suction tap regardless of which mode I'm in, just don't want to run in to the situation were I think im going to be using cooling mode and the reversing valve doesnt switch and I destroy my guage). Maybe I'm just paranoid.
i agree a charge compensater works that way, but how many residential systems have these installed? i was disagreeing with the system needs more refrigerant in cooling than heating.....are we going out every spring to add charge, and every fall to remove it?
Sorry for the miss-understanding. What I was trying to get across was simply that it is better to charge in the cooling mode at manufacture specified OAT. However, we don't live in that magical world. Yes it is best to weigh charge in ( keeping mindful of line length). If weight info is nowhere to be found or line length is not able to be determined for example lines behind walls and or condenser is 3 doors down and on the other side of the street because that's were the architect decided it looked good there, SC and SH can be used. The miss understanding in the difference in refrigerant amount between heating and cooling was not explained well my bad. What I meant was when you do charge in cold conditions in the heating mode you may find when in warm conditional and the unit is switched to cool you may find the unit to be a few ounces low. This is do to the slight loss of capacity in the heating mode and conditions compared to the cooling mode and conditions. The accumulator is there to protect the compressor in the cool/ cold condition to prevent slugging the compressor. I guess the point I was trying to get across was it is not a bad practice to make a visit in the spring or early summer just to verify the charge is correct, to ensure the customer is getting the full performance from there system. Sorry for the miss understanding.
And yes I do agree that the difference in the size of indoor and out door coils does have a contributing factor as well. Maybe not as much in an air to air heat pump but the logic can be somewhat corilated to a Direct Exchange Geo. I know it's a totally different beast but none the less the basic principle is there.
Using similar logic (albeit simpler) to the above, if the indoor unit coil was 1 and the outdoor unit coil was 2, then in cooling mode:
2 + 1 = 3
In heating mode:
1 + 2 = 3
In heating mode the outdoor coil is obviously the evaporator and since it is generally larger than the indoor coil the refrigerant by design should be superheated by the time it hits the accumulator, if the system is operating within design conditions of course.
Riddle me this:
Why is it that one can charge a heat pump in cool mode, it runs fine all summer. Then come winter time, the system performs poorly, produces symptoms of overcharge, then performs just fine once some refrigerant is reclaimed?
What I'm trying to say is that its easy to overcharge a heat pump in cool mode, because it will use more refrigerant in cool mode.
And NO, we don't go out in the fall, pump some refrigerant out and return in the spring to put it back in. However, a heat pump is critically charged, slightly overcharged it will perform poorly in heat mode, slightly undercharged it will perform poorly in cool mode.
Bottom line, a charge that is considered "undercharged" in cool mode will perform fine in heat mode. Why? Because the system doesn't need the extra refrigerant that it needs in cool mode.
I actually think we are all saying very similarly the same thing, only in a bit different way. While we can pretty much make any indoor coil work for a cooling only application by metering and charging to that particular coil and metering device, when we start changing up the indoor coil function and the outdoor function, the two coils either need to be close in physical capacity or some sort of charge compensator, collector of refrigerant if you will, to keep the refrigerant charge controllable in both heat and cooling modes.
All of the methods of charging in the winter will get you close. But there isn't any way you can be absolute without know the exact specs. And weighing it in. The accumulator is designed for keeping liquid from getting to the compressor but its because one mode requires more refrigerant than the other. It's simply because while running in the heat pump mode as the ambient temp. Drops and/or frost begins to form on the coil flooding will occur
Find a unit with a chart and take a picture on your cell phone so you can refer back to it. I took a pic of one for 22 and 410. It will get you close. You definitely need to hook your gauges up. A rule of thumb for temp rise that I was taught is at 32*F oat the temp rise will be 20. For every three degrees +/- oat the temp rise will be 1 degree up or down. That is based on proper airflow and proper charge. Dirty coils/ filter and it will definitely change.
I often wondered if these charts where unit specific. So a carrier chart should get me close ona goodman or rheem unit?