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suction line sizing

January 10, 2019

The issue:

This is a residential setting, 10 year running, 4 ton R22 split system, single story home, evap in the attack, no more than 60 feet from compressor on ground level. Initial install, had the copper suction and liquid lines, 7/8″ and 3/8″ respective, running down exterior wall. I had the installer change the piping to run down through an interior wall (closet), under the house and out the vent to the compressor. When he returned to do this change, he brought 5/8″ tubing, not 7/8″. He made a suction line connection from 7/8″ to 5/8″ in the hall closet wall. From that connection, the 5/8″ tubing run is approximately 20′ to the compressor. There are no other fittings involved, everything else is nice smooth sweeps. As sometimes happens, you get convinced that it’ll be alright. Well, years later, everything seems to run fine but that connection is ugly and I wonder if it has an affect on my system, or that it will leak some day. I’m about to go back and finish out the closet cabinetry and want to close up this wall. I am considering having a local A/C mechanic look at it for another opinion… what do you suggest?

Comments (5)

  • mike_home

    If the connection has not leaked in all these years then it is not a concern. These types of connections tend to look ugly but if it was done properly I wouldn't worry about it.

    The real problem is what are you going to do when you have to replace this AC. A new AC will be using R410A refrigerant. The line set is usually replaced when the refrigerant is changed but some will do some kind of flush and claim it is good. Even if you were to flush the line the 5/8 inch line may not be the proper size for your new condenser. So you either have to open up the closet wall to replace the line or run the new line on the exterior.

    HU-969834487 thanked mike_home
  • Elmer J Fudd

    Each compressor has install specs for the lineset - max distance, max height of coil above condenser, pipe diameters considering the preceding, etc.

    If you really want certainty, put in a new system that's correctly done to specs and be done with it.

  • HU-969834487

    Thank you Mike_home...

    But that's exactly my issue, sweating in a 7\8 to 5\8 inch fitting without using a reducer to me is negligent. Also, I was hoping someone would recognize and explain the necessity of running same size suction line from evap to condenser, I really thought someone would take exception to this configuration. I am not an HVAC trades person, but have worked mechanical for 37 years in electrical generation as mechanic alongside with many other crafts. I have always expected work to be done in an acceptably craftsman like manner. I let this go for all these years because life happens. Now its my focus again and I want to call it done. To answer the question of replacing the suction line for upgrade, this unit has hardly any years on it, and doesn't run excessively due to conservative therm setting and proper insulation.

    Thank you again,


  • mike_home

    If you know the model number of the condenser then you may be able to find the installation document. That document will show what is the diameter of the suction line for the 4 ton size. It is probably going to indicate 7/8 inch. The documentation may show it as the outside diameter so read the document carefully. If that is the case then the 5/8 inch diameter is restricting the vapor flow and reducing the performance of the condenser. You may not be noticing this if your AC is over sized for your house.

    I am not an HVAC trades person either, but how do you change diameters without some type or reducer? Maybe the best option is to replace the 5/8 line with a 7/8 diameter and have it done by somebody who will do it properly.

    Would it be possible to install an access panel where this connection exists? That would allow you to get to it in case there was a problem in the future.

  • sktn77a

    If it bothers you that much, get it replaced. It won't be cheap - I'm guessing around $600 to evacuate, replace, run a vacuum and recharge.

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