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pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Reviews:
·Comcast

Checking R410a Charge on Heatpump in Cold Weather

I am about to have a 2 year old Carrier Heatpump serviced for the first time and have a question about procedures for checking the system charge.

Since the evaporator has a TXV valve the proper method to determine charge is from the subcooling. As near as I can tell, basically you measure the pressure on the liquid line, convert this pressure to a saturated temperature. Subtract the subcooling requirement from this temperature and compare the result to the actual measured temperature on the liquid line. Add/remove R410A as needed to get the proper subcooling.

Sounds simple in theory for the summer, but how do you do this in the winter when the heatpump is running? Do you put the system in cooling mode to do this check? Would this check be accurate/possible if the outside temp is 40*?

Also how critical is it to get the charge EXACTLY right? By this I mean what is the impact of lets say, the system being 2 oz low?
--
The difference between genius and stupidity is that genius has its limits.



Sly
Premium
join:2004-02-20
Chuckey, TN
kudos:1
Reviews:
·Callcentric

1 edit

Normally you would run it in cooling mode and put a restriction around the outside condenser. Something like cardboard... The air restriction will cause your head pressure to rise up enough to make subcooling accurate. 2 ounces won't make any difference but a pound either way could.

[edit] Changed evaporator to condenser...



charge

@myvzw.com
reply to pende_tim

I usually charge by weight in the heating season and then recheck when warm weather returns. If the system charge is slightly low, the evaporator will run a bit cooler which isn't a big deal in heating mode. 2 ounces one way or the other will have very little, if any effect on system efficiency.



Jack_in_VA
Premium
join:2007-11-26
North, VA
kudos:1
Reviews:
·Millenicom
reply to pende_tim

said by pende_tim:

I am about to have a 2 year old Carrier Heatpump serviced for the first time and have a question about procedures for checking the system charge.

If you are having it "professionally" serviced they know how to check it.

I have my units serviced twice/year. In the sprint and in the fall when the weather is not either hot or cold. That schedule has been working fine for years now.


pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Reviews:
·Comcast

Yes it will be professionally serviced however the unit has never been serviced and I do not have experience with the company/person doing the work. Since it is now working, I don't want to see it's performance degraded through incompetence.

I wanted to learn 2 things from this thread:

1. Confirm if it can be correctly and accurately checked for proper charge during cold weather or if this time of year, it got a "lick and a promise" and just a close estimation of charge levels. If that were the case, I would have put off the service until hotter weather.

2. Find the procedure the tech would using to check the charge if it was even possible to accomplish.
--
The difference between genius and stupidity is that genius has its limits.



Jack_in_VA
Premium
join:2007-11-26
North, VA
kudos:1
Reviews:
·Millenicom

1 edit

said by pende_tim:

Yes it will be professionally serviced however the unit has never been serviced and I do not have experience with the company/person doing the work. Since it is now working, I don't want to see it's performance degraded through incompetence.

I wanted to learn 2 things from this thread:

1. Confirm if it can be correctly and accurately checked for proper charge during cold weather or if this time of year, it got a "lick and a promise" and just a close estimation of charge levels. If that were the case, I would have put off the service until hotter weather.

2. Find the procedure the tech would using to check the charge if it was even possible to accomplish.

If you have so little confidence in the company and tech that is trained and certified that will be doing the work that you would rely on information from this or any other forum that maybe or maybe not be accurate then IMO you need to get another company that will give you a higher trust level.

* Yes the charge can be checked. How do you think they install them year round hot or cold? My Trane was installed in February

** Unless there's a certified Carrier tech on here you won't get the Carrier recommended procedure.


Sly
Premium
join:2004-02-20
Chuckey, TN
kudos:1
Reviews:
·Callcentric
reply to pende_tim

There are 2 ways they may properly charge the system. Most likely they will simply weigh the charge in. That involves fully evacuating the system and then recharging it by the weight stamped on the side of the unit.

The other way involves charging by subcooling, which you already mentioned. If they try this in low ambient conditions, they will have to artificially raise the head pressure. Let the system heat up as it would in summer... They do this by covering the outdoor unit to restrict air flow. The house must also be above 70 degrees so that it gets a proper heat load when they switch on the air conditioning. Subcooling takes much longer and will be more expensive, but I personally prefer this method as it accounts for all of the system variables and ensures a proper charge.

If a system is overcharged, it will cause your electric usage to increase and your head pressures will be higher. The metering valve will prevent flood back of liquid to the compressor like you would have with a metered orifice system, but it would still not be ideal. If the system is undercharged, your TXV will not get enough liquid and the refrigerant will flash boil too soon in the evaporator. Your superheat will be too high and the compressor will run too hot, increasing wear and electric usage.

The "exact" charge is really just somewhere in the middle where you have minimal head pressures and proper superheat. Your heat pump works in a variable environment so the exact charge needed for one day may be different than the charge needed for another day. Just as long as they don't have it drastically undercharged or overcharged, everything should be fine.


guppy_fish
Premium
join:2003-12-09
Lakeland, FL
kudos:1
reply to pende_tim

If it ain't broke, don't fix it ....



pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Reviews:
·Comcast
reply to Jack_in_VA

Hi Jack,
It is not that I don't trust the company, I just want to be an educated consumer and know what to expect and what is possible. Too much watching Holmes on Homes, I guess.

Tim
--
The difference between genius and stupidity is that genius has its limits.



Jack_in_VA
Premium
join:2007-11-26
North, VA
kudos:1
Reviews:
·Millenicom
reply to Sly

said by Sly:

There are 2 ways they may properly charge the system. Most likely they will simply weigh the charge in. That involves fully evacuating the system and then recharging it by the weight stamped on the side of the unit.



That procedure is not likely to be used unless the unit has been evacuated.

The other way involves charging by subcooling, which you already mentioned. If they try this in low ambient conditions, they will have to artificially raise the head pressure. Let the system heat up as it would in summer... They do this by covering the outdoor unit to restrict air flow. The house must also be above 70 degrees so that it gets a proper heat load when they switch on the air conditioning. Subcooling takes much longer and will be more expensive, but I personally prefer this method as it accounts for all of the system variables and ensures a proper charge.

Just heat up the house and put the unit in defrost which stops the fan eliminating the "need" to try to cover the outdoor coils. Defrost is the cooling cycle without the fan on the condenser running therefore raising the head pressure. It doesn't take long for that with no airflow across the coil.

If a system is overcharged, it will cause your electric usage to increase and your head pressures will be higher. The metering valve will prevent flood back of liquid to the compressor like you would have with a metered orifice system, but it would still not be ideal. If the system is undercharged, your TXV will not get enough liquid and the refrigerant will flash boil too soon in the evaporator. Your superheat will be too high and the compressor will run too hot, increasing wear and electric usage.

The tech will make the necessary adjustments to the refrigerant when he makes his checks.

The "exact" charge is really just somewhere in the middle where you have minimal head pressures and proper superheat. Your heat pump works in a variable environment so the exact charge needed for one day may be different than the charge needed for another day. Just as long as they don't have it drastically undercharged or overcharged, everything should be fine.

The unit has a chart or table to tell the tech what parameters for the conditions that day the unit should be.

ncbill
Premium
join:2007-01-23
Winston Salem, NC
reply to pende_tim

Why do you think the charge needs to be checked?

It's a sealed system after all.

Unless you think your original installer screwed up, but I'd think that would cause problems sooner than 2 years.

said by pende_tim:

Hi Jack,
It is not that I don't trust the company, I just want to be an educated consumer and know what to expect and what is possible. Too much watching Holmes on Homes, I guess.

Tim