walked into a prior company's mess
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  1. #1
    Join Date
    Jun 2005
    Location
    Winston-Salem NC
    Posts
    1,133
    Had a service call last year for no cooling. Unit had a rheem 3t hp with a locked scroll compressor. Busy season, compressor under warranty and dirty O/D coil. Changed compressor, including installing high acid capacity filters,flared of course to make the 72 hour change out easier. Whole change out by the book, cleaned coil, etc. Came back three days later change filters, checked charge, everything fine and dandy.
    Couple days ago, no cooling at same unit. Went and fond compressor out on thermal, and not coming back on.
    This time did the entire system, and found a 2.5T, 11 SEER indoor coil, that some professional had cut the TXV off, and installed a piston on.
    Told the owners that they were SOL, needed a new system, got the go ahead, ordered a trailer rated, yeah it's in a double wide, split system of the proper size;3T, and when it came in went to job and started the change out.
    Had the O/D unit off and was starting on the A/H when my helper pointed out that the new system was too big by 2.5" to go back into the closet. At this point talked to the owners, who account for about 30% of my yearly gross, and explained the options.
    Decided to go back with a compressor change out, but could not get the head to come up past 165psig, on a 85 deg day. Talked to a fellow who worked in the field for about thirty years before he started teaching and he told me that it was feeding hot gas from the O/D coil. Said try to get the head right and leave the suction to fend for itself.
    Well charged it until it was feeding liquid back from evap, and head moved to a high of 175psig.
    Reclaimed the excess and hooked in a low abient control to cycle head while in cooling and allow fan to run normal during heat mode.
    But some little bug in the back of my head is telling me that heat mode may be the culprit.
    As a note, this has become a self appointed mission of mine. Charged the owners for materials and at a low mark up. Nothing for labor. They have told me to put a heat pump package unit in when this fails, so right now it is a matter of me versus the machine demons.
    Of course, my old boss told me to put the package unit in and go make some money, but obsession is a hard habit to break.

  2. #2
    Join Date
    Feb 2004
    Location
    Maine
    Posts
    483
    Please post more info, superheat, subcool, run amps on label, running amps at compressor common, etc. Could be many things, from a reversing valve that is not engaged all the way and leaking by, to a restriction somewhere. Superheat and subcooling will tell you whats going on here. What is your metering device now? txv or piston? 1/2 ton mismatch won't cause your problems, wrong size or no piston will cause these problems though. Post the info and we will see if we can help.

  3. #3
    Join Date
    Apr 2004
    Posts
    7,680
    30 years experience is a weak argument. Frankly I get tired of hearing it. All that means is they have had an opportunity to create and live with 30 years of bad habbits. Let me say that this generally applies to anyone who makes the statement, but those who keep up with technology and training rarely resort to the longevity of thier experience to make a case.

    The Rheem unit is not rated for mobile homes as you have noted and the selection of the 2.5 ton coil is an indication of someone puting it in to fit the hole but still deciding, probably based on the sticker inside the door that they still need 3 tons outside for this home.

    It is likely that you will indeed continue to have problems making this right. Find a miller, or coleman unit to do the job or if you like the Rheem, go with the dedicated horizontal packaged heat pump which is rated for that application.

  4. #4
    Join Date
    Jun 2005
    Location
    Winston-Salem NC
    Posts
    1,133
    docholiday
    I have a Rudd/Rheem package unit picked out, specifically designed for trailers. It'll go in as soon as this garbage dump assortment of mismatched pieces fails.
    I was just wondering if the airflow,or lack of, accross the I/D coil in heat was the culprit in the compressor failure.

  5. #5
    Join Date
    Jun 2005
    Location
    Winston-Salem NC
    Posts
    1,133
    docholiday
    He doesn't make the arguement for his experience. His first response to my question was to jerk it out and put the properly rated and sized equipment in. Only when I pushed did he theorize that the head pressure was the problem, and suggest the idea of bringing the head up and allowing the suction to handle itself.

  6. #6
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,279
    Only when I pushed did he theorize that the head pressure was the problem, and suggest the idea of bringing the head up and allowing the suction to handle itself.

    This is where I would have a problem with thirty years of experience saying something like "allowing the suction to handle itself" and "bringing the head up".

    If a technician with five years of experience went on this job and came back with extensive data on this trailer's system such as superheat, subcooling, amp draw, delta T over both coils, any unusual temperature differences across reversing valves or check valves or accurators, etc., I'd tend to look upon that more favorably than "allowing the suction to handle itself" to indicate someone with far greater time in the saddle has any firm grasp on refrigeration principles.

    Sorry, I gotta agree with doc's call on this one (although credit is due where your source recommended proper equipment for application).
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  7. #7
    Join Date
    Apr 2004
    Posts
    7,680
    Glad to hear he suggested that much but his comment to set the head and let the suction handle itself is left over from 30 years ago with cap tubes and has not applied to a single unit made since 1991. Thats my point about experience. If he's actually applied that to any modern equipment hes probably killed more compressors than you or I can imagine and never thought twice about the wake he leaves behind him.

    It could have been part of it but I can only guess at the other things that may have also contributed. Most likely airflow issues in both heat and cool. Those doublewides have undersized ductwork and the Rheem air handler will not push against those high statics meaning low airflow, meaning compressor slugging in cooling and overcharged system in heating. When you have low airflow and try to use the charging charts you will overcharge the system. Imagine the system in heating mode...where is all that excess refrigerant to go? Not to mention defrost issues.

    That package unit you have chosen can drive higher statics.


  8. #8
    Join Date
    Mar 2004
    Location
    Grottoes VA
    Posts
    5,856
    You can use a Rheem condensing unit if you like, and it will work fine if you use a Coleman/Miller trailer furnace and an allstyle coil.
    Karst means cave. So, I search for caves.

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