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Thread: R22 to R407C change over

  1. #1
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    R22 to R407C change over

    I'm a new, self taught tech. I was hired by a small oil company which has a service department. Their AC guy recently left so I'm trying to get up to speed.

    I just changed out an R22 outdoor unit with a R407C outdoor unit. The R22 outdoor unit had failed because the owner's dogs frequently urinated on the condensor coils. The unit had run some time with no refrigerant.

    I diagnosed the failure, and closed the service valves and left the line set and evap coil under pressure with nitrogen.

    I released the nitrogen, connected the new outdoor unit, pressure tested with nitrogen. Then I pulled a vacuum to less than 500 microns and released the refrigerant. As I was pumping it down the pressure didn't fall evenly, I think there was some moisture in the system.

    The R22 outdoor unit I removed came with 3 lbs of refrigerant. It wasn't marked if more had been added so I assumed that was the charge it had.

    The outdoor unit I installed came with "dry 407c" meaning it had 1 lb of R407C so it could be sold as an "R407C" unit even though it often is evacuated and charged with R22.

    The day I installed the new outdoor unit it was only 61 degrees out. I was afraid of possibly overcharging the system so I added 2 lbs of R407C to bring it to a total charge of 3 lbs. The new outdoor unit is rated the same tonnage as the one that it replaced, but the condensor coil is much bigger. I don't know if that necessarily indicates that it holds more refrigerant.

    As I added refrigerant I started seeing the numbers come more or less into line. Granted the temperature was not ideal for charging.

    As I charged the system the suction line temp dropped below the liquid line temp. When I had added the 2 lbs of R407C for a total of 3 lbs I had the following readings:

    Suction line 75.5 PSI
    Liquid line 128 PSI
    Suction line temp 51.3F
    Liquid line temp 63.5F
    Superheat 3.5F
    Subcooling 1.0F

    As I added charge the superheat went from 40 down to 10 so I stopped charging but it continued to drop.

    I was afraid to charge the system too much as I know bad things happen if liquid gets back to the compressor.

    Why is the superheat and subcooling so low?

    Is the system under charged? Thanks guys!

  2. #2
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    The R407C is a 14 SEER rated system, the old unit was probably a 10 SEER hence smaller coil.
    Last edited by Bazooka Joe; 05-08-2021 at 10:50 AM.

  3. #3
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    You’ll need to prove your credentials and get pro status before getting troubleshooting help...this has diy written all over it.

    Why would you do that instead of replacing the entire system with a 410 system???
    "I think Quantum tunneling would work great... "

    "Call a technician for God's sake. Or we'll see you on the news or the Dark Side of the Moon."

  4. #4
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    Quote Originally Posted by JayMan7 View Post
    You’ll need to prove your credentials and get pro status before getting troubleshooting help...this has diy written all over it.

    Why would you do that instead of replacing the entire system with a 410 system???
    Thanks for the reply. I have applied for pro status.

    The decision to replace only the outdoor unit was made by my boss and the customer. The decision was based on cost.

  5. #5
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    well if ur outdoor ambient is 61* I would imagine liquid pressure should be higher, i would say more like 165psi. I would add more refrigerant to bring up ur liquid pressure and subcooling then adjust ur txv (assuming its the correct metering device for your application) and that will bring ur superheat back up. that being said you probably wont get 100% great readings. hindsight 2020 putting a new r410a condenser and matching indoor coil woulda been the way to go I've seen quite a few people in my area try to save money doing this kind of stuff and it never performs correctly for a reasonable amount of time. What TD are you getting.

  6. #6
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    You should probably define what TD is. Many on here have no clue you are asking about something that involves the saturation of the coil. By the way, which coil are you asking this question about?


    Quote Originally Posted by TheReefer View Post
    well if ur outdoor ambient is 61* I would imagine liquid pressure should be higher, i would say more like 165psi. I would add more refrigerant to bring up ur liquid pressure and subcooling then adjust ur txv (assuming its the correct metering device for your application) and that will bring ur superheat back up. that being said you probably wont get 100% great readings. hindsight 2020 putting a new r410a condenser and matching indoor coil woulda been the way to go I've seen quite a few people in my area try to save money doing this kind of stuff and it never performs correctly for a reasonable amount of time. What TD are you getting.
    I do a triple evac with nitro to remove non condensables.

  7. #7
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    My bad for not being specific enough but by TD i mean Temperature Differential across the Evaporator Coil. That being said if you don't know what that is you probably shouldn't be charging refrigerant into anything lol.

  8. #8
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    Quote Originally Posted by TheReefer View Post
    well if ur outdoor ambient is 61* I would imagine liquid pressure should be higher, i would say more like 165psi. I would add more refrigerant to bring up ur liquid pressure and subcooling then adjust ur txv (assuming its the correct metering device for your application) and that will bring ur superheat back up. that being said you probably wont get 100% great readings. hindsight 2020 putting a new r410a condenser and matching indoor coil woulda been the way to go I've seen quite a few people in my area try to save money doing this kind of stuff and it never performs correctly for a reasonable amount of time. What TD are you getting.
    Thanks! I didn't think it was fully charged but I felt better erring on the low side of charge rather than high for fear or getting liquid returning to the compressor.

    Thanks for the input about the disadvantages of replacing just the outdoor unit and going to R407C rather than replacing the whole system with R410A components.

    I didn't measure the delta T but the returns were cool.

    I plan on going back when the ambient is more favorable.

  9. #9
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    Low SH generally indicates overfeeding or at least enough refrigerant, are you measuring SH at the coil or at the comp?

    Does this unit have a TXV?

  10. #10
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    Quote Originally Posted by Olivero View Post
    Low SH generally indicates overfeeding or at least enough refrigerant, are you measuring SH at the coil or at the comp?

    Does this unit have a TXV?
    TXV. At the compressor. Thanks

  11. #11
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    I'll wait a little longer to reply to see how much more info is supplied which is not completely correct.

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  13. #12
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    The outdoor unit I installed came with "dry 407c" meaning it had 1 lb of R407C so it could be sold as an "R407C"

    That's a new one on me, Never heard that!

  14. #13
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    As I charged the system the suction line temp dropped below the liquid line temp.

    Isn't that what's supposed to happen?

  15. #14
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    May be a time for a little more honesty.....................

    How much experience do you have?
    Last edited by pecmsg; 05-08-2021 at 07:30 PM.

  16. #15
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    Quote Originally Posted by takoateli View Post
    TXV. At the compressor. Thanks
    Suction line 75.5 PSI
    Liquid line 128 PSI
    Suction line temp 51.3F
    Liquid line temp 63.5F
    Superheat 3.5F
    Subcooling 1.0F
    3.5˚ superheat with a TXV indicates the valve is overfeeding, which could be due to the different P-T relationships of 22 and 407C, which is 3.5˚±. At 75 psi, the valve is "seeing" a 22 saturated temperature of 44˚ and controlling to 7˚ superheat. Or, it could just be funky and overfeeding...

    The low subcooling and head pressure supports an overfeeding symptom...but 60˚ OD is pretty low and would effect some over condensing.

    Best conclusion at this point is check the system at a warmer OD value...if you can add refrigerant and maintain 3˚ superheat then the valve is OK. But if more freon (increased head pressure) causes lower superheat, then you'll have to do something with the valve...adjust if it's an option or replace with an adjustable model.

  17. #16
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    That's TS. Temperature split, sometimes called delta T. Which is why I questioned if you were using the proper terminology. TD is something else.


    Quote Originally Posted by TheReefer View Post
    My bad for not being specific enough but by TD i mean Temperature Differential across the Evaporator Coil. That being said if you don't know what that is you probably shouldn't be charging refrigerant into anything lol.
    I do a triple evac with nitro to remove non condensables.

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  19. #17
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    Quote Originally Posted by pecmsg View Post
    May be a time for a little more honesty.....................

    How much experience do you have?
    Yeah I’m surprised no one else has mentioned the numerous red flags on this one.
    "I think Quantum tunneling would work great... "

    "Call a technician for God's sake. Or we'll see you on the news or the Dark Side of the Moon."

  20. #18
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    Quote Originally Posted by pecmsg View Post
    May be a time for a little more honesty.....................

    How much experience do you have?
    Quote Originally Posted by JayMan7 View Post
    Yeah I’m surprised no one else has mentioned the numerous red flags on this one.
    Quote Originally Posted by Takoteli
    I'm a new, self taught tech. I was hired by a small oil company which has a service department. Their AC guy recently left so I'm trying to get up to speed.
    His opening sentence establishes his level of experience and credentials...

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  22. #19
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    ya ur right you'll have to forgive me as its one of those things that everybody calls it in my area differently than the book, kinda like how i hear so many people call refrigerant freon. but ya ur right and i was actually asking about temp split technically.

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  24. #20
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    R22 to R407C change over

    Quote Originally Posted by Saturatedpsi View Post
    His opening sentence establishes his level of experience and credentials...
    You’re definitely right. I think I should have kept that opening statement in mind.

    I think the issue is that countless numbers of people have gotten on the forum posing as an inexperienced tech when they are actually a diyer or just simply should not be doing what they are doing...that’s the red flags I’m referring to. Now the OP could be perfectly legitimate, but the forum rules still apply.

    I do feel sorry for techs that get in over their head and come to the forum for help, but I also feel sorry for all the people that suffer at the hands of unqualified contractor or diyers. Most of us who have bought a house that’s been “remodeled” understand just how bad this problem is.

    Once the OP gets access to the locked areas I’m sure it will provide lots of support, and I hope they find it extremely useful.

    But for this issue it sounds like the oil company needs to make a service call and bring in another tech to be there in person and troubleshoot the system. Then the OP can make the repair if necessary. There would be no shame in that, and it’s probably the best option. Replacing an ODU on an old IDU that may not even be working right is just asking for problems.
    Last edited by JayMan7; 05-09-2021 at 07:00 PM.
    "I think Quantum tunneling would work great... "

    "Call a technician for God's sake. Or we'll see you on the news or the Dark Side of the Moon."

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