Basic Air Conditioning Piping Recommendations – Introduction

A split system air conditioner consist of more than the box sitting outside.  That is just one component of an entire system. Since this is a system, specific application considerations are required with regards to the rest of the system — air handling unit, duct design, control scheme, and refrigerant piping.

In other posts, we have discussed controls and proper air flow.  In this post, I’ll try to look at proper refrigerant piping which is often overlooked and not properly applied to the system.  Improper piping practices can cause loss of capacity, poor oil return leading to compressor failures, noise issues, just to name a few. So let’s get started and look at what we need to consider when piping an air conditioner.

The first thing to remember is that every split system unit is equipped with a factory provided sweat fitting.  This could be a service valve or something as simple as a capped copper stub.

Service valves 2

For cooling systems where the indoor and outdoor sections are installed at about the same “elevation” and are not longer than 50 to 75 feet, refrigerant lines can usually be matched to the factory fittings. Once the job requirements start deviating from this simple application, line set sizing really needs to be looked at and performed to assure a properly operating system.

In some applications, especially where elevation differences exist between the indoor and outdoor sections, suction and liquid line sizes can be increased or decreased to minimize a pressure loss or gain on the system and to improve oil return to the compressor.  When sizing lines for split systems cooling units, the following factors MUST be considered:

  1. Suction line pressure loss due to friction
    1. diameter and elbows add to friction loss
  2. Suction line velocity for oil return.
  3. Liquid line pressure loss due to friction.
  4. Liquid line pressure loss or gain due to “static head”
    1. “pushing” liquid up a riser causes a pressure loss
    2. liquid “dropping” down a riser causes a pressure gain

The effect that each of these factors have on a cooling system depends on the orientation of the indoor section to the outdoor section and if  staging or capacity reduction is involved in the system.

In my next few post, I will try to address different installations, elevation differences, and general guidelines for proper refrigerant piping.  Hopefully this will help you to better apply split system cooling systems to achieve maximum efficiency and performance and improve reliability.

About yorkcentraltechtalk

I have been in the HVAC industry most of my life. I worked 25 years for contractors on anything from residential to large commercial boilers and power burners. For the past 23+ years I had been employed by York International UPG Division ( a division of Johnson Controls) as a Technical support/Service Manager but I am now retired. One of my goals has always been to "educate" dealers and contractors. The reason for starting this blog was to share some knowledge, thoughts, ideas, etc with anyone who takes the time to read it. The contents of this blog are my own opinions, thoughts, experiences and should not be construed as those of Johnson Controls York UPG in any way. I hope you find this a help. I always welcome comments and suggestions for postings and will do my best to address any thoughts, questions, or topics you may want to hear about. Thanks for taking the time to read my postings! Mike Bishop
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6 Responses to Basic Air Conditioning Piping Recommendations – Introduction

  1. Dan Trachsel says:

    Nicely done! I appreciate your tips. I am the Technical Specialist person for Johnstone Supply, NW. I wanted to say that your articles are spot-on and timely, please keep them coming. Do you have any restrictions on re-printing/re-producing your articles as long as credit is given to you? Would credit be given to Yorkcentraltechtalk, or do you prefer to have your name used?


    Dan Trachsel

    • Dan — THANK you for the nice comment.
      My posts are “public” — in fact, a lot of distribution print them out and put them on their counters — I encourage that. I do it in my own office. I also enocouarge customers to use the “subscription” box (have 136 people following this site to date)
      Thanks again for your support — As long as I feel a need, I’ll try to keep blogging.

  2. roger daigle says:

    Mike, perhaps you talk about oil traps and their placement in the system. I haven’t seen one yet in a residential application.

  3. shibin says:

    i have a doubt in ac piping, i used 3/8 pipe in liquid line in ac outdoor unit 518, it is less than 16 ft. the recommended size is 2/8 . now my consultant told me to change to 2/8. do i have any suggestions for that. it is very difficult to change it now.

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