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  1. #1
    Join Date
    Apr 2013
    Location
    Warren, OH
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    14

    Residential HVAC/Residential Refrigeration Tech going to Light Commercial

    Hello!

    I am currently in the process of switching jobs doing Res HVAC/R to doing light commercial. Mainly Walkin Coolers, Freezers, Ice machines. All the work will be done in gas stations. The company thats hiring me knows my experience level is residential, and are willing to train me in the light commercial side of things. Now, since central AC is so easy, i feel i've been spoiled after going through my old school books while brushing up on my knowledge. Certain things are making my head spin, and was wondering if i could get some input.

    -Head Master Controls are confusing me big time. To my understanding, when charging a Head Master control system, if you charge in the summer time by filling the sight glass, you'll be able to hit your desired head pressure (ambient+30, converted to pressure), and low side (20 degrees colder than box temp) relatively easy. looking for 6-8 super heat on cooler, 4-6 super heat on freezer. However, once the cold weather comes, and the head master control kicks in, my charge won't be right anymore. Now, ive heard various theories on how to charge properly. One way i heard was charge to sight glass in summer, and add 2 lbs per h/p. Another is full sight in summer, plus 20% of capacity.

    Now, those charging methods are done by adding to exising refrigerant. For example, leak in evaporator. Pump down into receiver, change evap, pull vaccum, and then add to sight glass till clear and either add 2 lbs per h/p or 20% of capacity. Is any of this true? Is it possible to add to existing refrigerant with head master, or do you have to evacuate system and then weight it all in?

    Also, while charging Residential Central Air, charging is done by sub cooling if unit has TXV, super heat if unit has fixed orrifice. Checking superheat back at compressor and sub cooling at outlet of compressor, while checking humidity with psychrometer and outside temp. Is this still true with package AC and light commercial split AC systems?

    Thank you!!

  2. #2
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,567
    Quote Originally Posted by EricDMKAJ View Post
    Hello!

    I am currently in the process of switching jobs doing Res HVAC/R to doing light commercial. Mainly Walkin Coolers, Freezers, Ice machines. All the work will be done in gas stations. The company thats hiring me knows my experience level is residential, and are willing to train me in the light commercial side of things. Now, since central AC is so easy, i feel i've been spoiled after going through my old school books while brushing up on my knowledge. Certain things are making my head spin, and was wondering if i could get some input.

    -Head Master Controls are confusing me big time. To my understanding, when charging a Head Master control system, if you charge in the summer time by filling the sight glass, you'll be able to hit your desired head pressure (ambient+30, converted to pressure), and low side (20 degrees colder than box temp) relatively easy. looking for 6-8 super heat on cooler, 4-6 super heat on freezer. However, once the cold weather comes, and the head master control kicks in, my charge won't be right anymore. Now, ive heard various theories on how to charge properly. One way i heard was charge to sight glass in summer, and add 2 lbs per h/p. Another is full sight in summer, plus 20% of capacity.

    Now, those charging methods are done by adding to exising refrigerant. For example, leak in evaporator. Pump down into receiver, change evap, pull vaccum, and then add to sight glass till clear and either add 2 lbs per h/p or 20% of capacity. Is any of this true? Is it possible to add to existing refrigerant with head master, or do you have to evacuate system and then weight it all in?

    Also, while charging Residential Central Air, charging is done by sub cooling if unit has TXV, super heat if unit has fixed orrifice. Checking superheat back at compressor and sub cooling at outlet of compressor, while checking humidity with psychrometer and outside temp. Is this still true with package AC and light commercial split AC systems?

    Thank you!!

    http://sporlanonline.com/literature/90/90-30-1.pdf


    Print it, laminate it, read it twice and keep it in your van to reference.

    This is the best method that I've found for charging headmaster and ORI/ORD type systems.

  3. #3
    Join Date
    Apr 2013
    Location
    Warren, OH
    Posts
    14
    Nice!

    Stupid question, but is charging by that method done by evacuating the system and weighing it in? Or can you start charging based on that with refrigerant already present in the system

    (Edit) Oops, after reading it further, i see that it doesnt matter. it can be charged evacuated or with exising refrigerant

    Also, while charging Residential Central Air, charging is done by sub cooling if unit has TXV, super heat if unit has fixed orrifice. Checking superheat back at compressor and sub cooling at outlet of compressor, while checking humidity with psychrometer and outside temp. Is this still true with package AC and light commercial split AC systems?

  4. #4
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,567
    Quote Originally Posted by EricDMKAJ View Post
    Nice!

    Stupid question, but is charging by that method done by evacuating the system and weighing it in? Or can you start charging based on that with refrigerant already present in the system

    I'll *assume* that this is based on a refrigeration unit with a receiver, a headmaster and a sightglass.

    The charging method BEGINS with "Charge to clear the sightglass" Given that, you can start at any state of charge and properly charge the equipment.

    Read the document that I posted. Seriously.

  5. #5
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,567

  6. #6
    Join Date
    Apr 2013
    Location
    Warren, OH
    Posts
    14
    Wow, i can't believe i've never seen this information before. thank you thank you! And as far as the packaged AC, and split system AC, that is charged the same way as done in a residential setting i assume. gather ambient temperature, wet bulb, and follow chart just like you would normally, correct?

  7. #7
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,802
    Quote Originally Posted by EricDMKAJ View Post
    Wow, i can't believe i've never seen this information before. thank you thank you! And as far as the packaged AC, and split system AC, that is charged the same way as done in a residential setting i assume. gather ambient temperature, wet bulb, and follow chart just like you would normally, correct?
    Yep

  8. #8
    Join Date
    Apr 2013
    Location
    Warren, OH
    Posts
    14
    Thank you! This site is amazing. I know ill need a refresher on oil furnaces eventually, so this will definetely come in handy haha

  9. #9
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,567
    Quote Originally Posted by EricDMKAJ View Post
    Wow, i can't believe i've never seen this information before. thank you thank you! And as far as the packaged AC, and split system AC, that is charged the same way as done in a residential setting i assume. gather ambient temperature, wet bulb, and follow chart just like you would normally, correct?
    Yep.





    Just noticed that you're fairly close to me. I work the greater Y-town area into PA and WV

  10. #10
    Join Date
    Apr 2013
    Location
    Warren, OH
    Posts
    14
    Wow, small world. Poor Youngstown has gotten do depressed, hoping it turns around eventually. Another question....as far as fan cycle controls, im assuming to charge these properly, you have to keep the condenser fans running to know your high side (ambient + 30, converted to pressure). how would those be charged in the winter/summer? do you have to add the additonal winter charge for those like you would for a head master? i dont believe i would have to, im assuming i could charge it the same year round

  11. #11
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,567
    Quote Originally Posted by EricDMKAJ View Post
    Wow, small world. Poor Youngstown has gotten do depressed, hoping it turns around eventually. Another question....as far as fan cycle controls, im assuming to charge these properly, you have to keep the condenser fans running to know your high side (ambient + 30, converted to pressure). how would those be charged in the winter/summer? do you have to add the additonal winter charge for those like you would for a head master? i dont believe i would have to, im assuming i could charge it the same year round
    Most units that I see have a means of head pressure control like a Headmaster or ORI/ORD valving setup.

    Make sure the condenser fan is running, charge per the 90-30-1 that I posted and you will be fine.

    If if DOESN'T have a low ambient control valve, you're stuck on "best guess" charging methods.

    What I'll typically do is just follow the chart anyway. It has worked for me so far.


    The "ambient +30 doesn't always hold true, BTW. It's a fair "guess" particularly at high ambients but it is really only a guess. Once your ambient drops, that number flies off the roof.

  12. #12
    Join Date
    Apr 2013
    Location
    Warren, OH
    Posts
    14
    I understand everything you're saying, I just have one issue. The only way to charge by sporlans way is to first evacuate the system. Then, weigh in charge to sight glass. Then, depending on how much you weighed in (changing based on ambient), you take difference of that and what is supposed to be in condensing unit. So, just to be clear, there is no way to charge these correctly without first evacuating entire system? Sorry to be a pain...

  13. #13
    Join Date
    Apr 2013
    Location
    Warren, OH
    Posts
    14
    You know, I've read this sporland document all day, and it finally clicked. You have to evacuate system completely of refrigerant before starting this process. Then, you figure out the volume of condenser. Then, you weigh in refrigerant until glass clears. You subract the number you just added from your total, and that's the additional you have to add in. Correct? Thank you so much, I am a tech that fully believes in the science side of the trade, and hate charging based on WAG. Thank you. You're a life saver

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