Compressor Change-outs


Too often, I get the phone call that a replacement compressor is “bad out of the box”! Now, I won’t say that never can happen. However, it is even more suspect when the contractor calls and says the replacement compressor for the replacement compressor is also “bad out of the box”.  What are the odds of 3 compressors, all being worked on by the same contractor are all bad? Statistics show that a large percentage of compressors returned to the manufacturer have no problem detected and work when run tested at the compressor manufacturer’s facility.

Compressor manufacturers use to put a card / check list in the box with replacement compressors. For all I know, they may still do it.  This was a great little way to help make sure that the replaced compressor has a very good chance of “operating out of the box”.  The problem is, it is usually in the bottom of the box , with the rest of the papers that all get thrown out or used for kneeling on.  So they are never read.  Here is a copy of that card:

Compressor repl proced

If you look at the various line items, they make a lot of sense in helping make sure the replacement compressor is going to work when you are done installing it.

Let’s take each item on the card and expand on it.

    • “Followed the enclosed installation instructions?”  This gave you information about removal or the old and installation of the new. Proper brazing and other items. 
      • Installed a new liquid line drier? This should be done any time a system is opened. Too often, a compressor gets replaced and the drier does not.  The drier could be partially plugged and now the new compressor is showing “strange pressures” and the contractor thinks he has a bad compressor again.
      • Installed suction line filter drier? If the system was a “bad burn out” — this is essential in making sure the system gets cleaned properly. Replaceable core type driers are best for doing this.  Also, keep in mind that one the system is cleaned, the Suction Drier should alway be removed from the system.
    • “DETERMINED THE CAUSE OF THE ORIGINAL FAILURE AND CORRECTED IT?”  This, to me, is probably the MOST IMPORTANT step in any compressor replacement.  If the original cause of failure is not fixed, what do you think will happen to this new compressor?  Is there power problems? Are all the wires and termination in good condition? Is the condenser coil clean.  does the condenser fan motor work?  Ar the indoor filters clean? Is the blower moving enough air?  Is the indoor coil clean? And on, and on, and on.  In a number of posts I have said — the only thing that can go wrong on the refrigerant side of the system is  OVER-CHARGE, UNDER-CHARGE, AND NON-CONDENSIBLES —all other problems are external to this side of the system.  All need to be checked to make sure this compressor does not fail prematurely.
    • “Evacuated the System?This has always been a critical step in any air conditioning service when the refrigerant side of the system is opened but even more so when replacing a compressor. all manufacturer’s recommend a vacuum down to 500 microns.  Then seeing if it holds or rises back up.  If it rises back up and stops, it is an indication that you still have moisture in the system and need to continue to evacuate.  If it rises and keeps rising — there is a leak.  What better time to address this that when you have the system empty and open.  Pressurize with a trace of refrigerant and nitrogen.  Find the leak and repair it and then re-evacuate the unit to 500 microns and see if it now holds.   This is especially critical with systems that have P.O.E. oil since that oils is very hygroscopic (meaning it absorbs moisture) and needs to be evacuated well.
    • “Install the proper size capacitor?”  Probably one of the most overlooked items on single phase air conditioners.  This, along with any start capacitors and start relays should always be replaced when replacing the compressor. If the compressor had an “electrical failure”, these components are part of that “side” if the system.  One of the biggest mistakes I have seen contractors make over the years is replacing a start capacitor and NOT changing the start relay.  The major cause of start capacitor failures is a bad start relay.  This is “cheap insurance” when replacing any single phase compressor.  This also goes back to finding out why the original compressor failed in the first place.
    • Checked line voltage from the contactor?”  How often have you found that the points on the contactor are corroded or pitted causing voltage drops and problems? Probably more often that you would like.  A compressor is a motor  and it runs on electricity.  It needs proper voltage to operate correctly just as any other electrical component requires proper power to work.
    • “Wired power leads correctly?” This applies to both single phase and 3-phase compressors.  On single phase, do we have C (common), S (start), and R (run) to the correct terminals on the compressor and are they properly wired to the capacitor?  Did you realize that if you reversed start and run, you would reverse the rotation of the motor in the compressor?  Problem is it will only run like that for a short period of time and then the windings will fail and you will be replacing the compressor again.  Very important to make sure the compressor is properly wired.  On 3-phase scroll compressors, you need to verify that the compressor is turning in the right direction.  3-phase scroll compressors can only pump in one direction unlike a piston type compressor that does not care which way the motor is turning.

So there you have it. There is more to replacing a compressor — and doing it right — than just removing the old and brazing in the new.  It still all goes back to proper diagnostics and installation practices.

(card above was from a Copeland Compressor box)

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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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