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  1. #1

    PTAC compressor wiring issues

    Guys:

    Need some pointers on PTAC, or capacitor wiring. I'm in a small southern town hospital stuck with about 44 McQuay PTACs in patient rooms. Voltage: 208. Every summer I'm replacing about 1/3 of the compressors because they have shorted to ground, blown their terminals, etc. Replaced one last week & found an updated wiring diagram that came with the Tecumseh compressor.
    It showed power from L1 to START via the capacitor. L2 ran to the RUN, with another lead from RUN to the capacitor (maybe to power the capacitor?). McQuay schematic runs L1 to capacitor, to START through an overload switch. L1 just goes straight to RUN, with no lead to capacitor. No updated McQuay schematic.
    Wondering if I need to modify the PTAC wiring, putting a slave terminal on the compressor & running a line back to the capacitor, eliminating the L1 line to the capacitor & just running to START from the capacitor.
    Will this help eliminate my compressor replacements. No excuse for compressors to belly-up in less than a year.

    If that's not enough, there's no way to eliminate condensate, so the room walls & ceilings have been ruined from condensate overflowing the pans.

    Any feedback (sarcastic or otherwise)??

  2. #2
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,288
    Quote Originally Posted by paper road View Post
    Guys:

    Need some pointers on PTAC, or capacitor wiring. I'm in a small southern town hospital stuck with about 44 McQuay PTACs in patient rooms. Voltage: 208. Every summer I'm replacing about 1/3 of the compressors because they have shorted to ground, blown their terminals, etc. Replaced one last week & found an updated wiring diagram that came with the Tecumseh compressor.
    It showed power from L1 to START via the capacitor. L2 ran to the RUN, with another lead from RUN to the capacitor (maybe to power the capacitor?). McQuay schematic runs L1 to capacitor, to START through an overload switch. L1 just goes straight to RUN, with no lead to capacitor. No updated McQuay schematic.
    Wondering if I need to modify the PTAC wiring, putting a slave terminal on the compressor & running a line back to the capacitor, eliminating the L1 line to the capacitor & just running to START from the capacitor.
    Will this help eliminate my compressor replacements. No excuse for compressors to belly-up in less than a year.

    If that's not enough, there's no way to eliminate condensate, so the room walls & ceilings have been ruined from condensate overflowing the pans.

    Any feedback (sarcastic or otherwise)??
    I read your post a few times and don't understand what you're trying to convey as far as the wiring goes.

    You have a model number for your McQuay PTAC's?

  3. #3
    Join Date
    Dec 2005
    Location
    Vancouver BC
    Posts
    126
    I doubt that the OEM is miswiring the units causing them to fail. Typically when I see a run of PTACs losing their compressors it is because they have been abused/neglected either through improper installation or lack of maintenance. Considering that there was no thought given to condensate elimination, I would begin with looking at the install. I have seen installations where the condenser air or indoor air is restricted through poor installation. Coils that are plugged with dust are a common problem as well. is it condensate that is overflowing the pans or coils that are icing up and leaking? It is hard to imagine a PTAC installation that would not allow for condensate drainage because condensate just runs out the back of the unit to the outdoors.
    ___________________________________________
    These Are The Good Old Days

  4. #4
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,288
    Quote Originally Posted by seascott View Post
    \It is hard to imagine a PTAC installation that would not allow for condensate drainage because condensate just runs out the back of the unit to the outdoors.
    I would disagree.....most PTAC's are designed to handle there own condensation, under normal conditions. Weep holes are a last resort. PTHP's have temperature activated valves but that's another story.

  5. #5
    PTACs are disassembled & cleaned annually of semi-annually (by me). They are given a once-over, checked freeze-stat, amp draw, etc. Sealed units, so I have to install refrigerant ports, when needed. Condensate is supposed to hit the condenser fan and be flung (sp?) onto the coils, but it hits the diffuser screen & runs to the pan. Installation was in the '60s. Cooling unit slides into a wall sleeve vented to outside. Outside airflow is across compressor, thru fan & pushed out thru cond. coils. Evap. pan has drip tube that drips into squirrel-cage condenser fan. Still looking for wiring solution & ideas on blown compressors. Thanx for input.

  6. #6
    ascJ: McQuay PKES014. re: wiring--I'll need to verify at work before I clarify. Don't want to bark up wrong tree. Can't remember how Tecumseh runs L1.
    seascott: condensate running over pans & thru weephole. We have lots of humidity. Misapplication of unit design to be sure. We have vacuumed out up to 1 1/2 gallons of condensate from each of these units. Want to replace, but money isn't there. trying to figure out how to channel the condensate to outside. Some of the wall sleeves cant inward toward room space, sending swimming pools onto terrazzo floors. Disaster recipe.

  7. #7

    Condensate problems with McQuay Ptacs

    Not sure if you got your problems solved, but a couple of issues can cause condensate leaking back into the room. Slope of the unit is one issue. Due to building settling, etc. the wall sleeve can shift. There should be about 1/4" slope from inside to outside to ensure water flow to the back of the unit. Another problem specific to the McQuay K unit is the drain tube that runs from the evaporator drain pan to the back of the unit being too short. If it's too short, it will leak out the front of the unit.

    Regarding the compressor failure, the K units are pretty heavy duty with a low failure rate. I work for a McQuay Distributor and have been selling these for over 20 years. Air flow restrictions/lack of maintenance will kill the compressor quickly. If that's not an issue you could check your voltage for highs/lows. Rotary compressors are not as tolerant to voltage fluctuations as the old recips. If you are still having problems, message me here and I'll see what I can do.

    Peace,

    Greg McNary
    Air Distributors Company, Inc.

  8. #8

    PTAC condensate issues

    McNary:
    Sorry it's been a long time in reply. Had to go out-of-state for awhile. I am currently working with McQuay on the compressor issue. It's beginning to point to inadequate airflow thru the front louvres. The original wall sleeves were built for the old Remington units whose condenser efficiency was not as great as the McQuay replacements. I can list the exact dimensions, but for brevity, we have about 59% of the louvre space for airflow. McQuay needs 70% or more. Inadequate airflow = cooked compressors. Regardless, I replace more than 1/4 of my compressors during a cooling season (Mar-Nov).
    I already addressed the drain issue with a 4" piece of 1/2" copper. Works like a charm. The building these were installed in was constructed in 1963. Lots of settling and some rather careless installations. Lots of condensate is running backwards. Experimenting with cotton rope wicks. A little cumbersome & marginal success at best.

    Thoughts?

  9. #9

    PTAC Condensate/Airflow issues

    Regarding the airflow, we had a similar situation with a local customer a few years back. They have the old Remington "D" vintage K units with the Remington room cabinets/front covers. Their original units date back to the early 60's, same as yours. The problem they had was twofold. When they started to replace units, they only replaced the cooling chassis. Normally this is OK, but since they have hot water heat coils that had 40+ years of dirt and crud built up, we recommended they also replace the entire heat section as well. 6 months later we're into cooling season and they are losing compressors like crazy. We got McQuay Service to take a look at their request, and found that the air flow was restricted about 80% or more. After checking some evap motors, most of them were barely running. They changed some of these out, cleaned a couple of coils, and voila, we have air! Shortly after they started changing out all of the motors or the complete heat section and haven't lost a compressor since. Not sure which type of heat you have, electric strip or hydronic, but check your motor speed. If it's too slow change it out.

    Regarding the louver space, you can change out the room cabinets to the current style. This will probably require changing the heat section as well. It's an expensive fix, but it will stop the compressor loss. If you have had significant settling, it may require removing the sleeve and reinstalling/replacing to get the proper slope for condensate drainage.

    For more info on the K unit and it's various components, I have posted the full catalog for you at
    http://www.airdistributors.com/userf...e/Cat_1302.pdf

    Let me know if you need more info.

    Greg McNary
    Air Distributors Company, Inc.

  10. #10
    McNary:

    You're the first to hit the nail on the head. My situation almost exactly mirrors your description. Hydronic heat & all. We did get the new cabinets & repiped the hydronics, but I'm still losing compressors. I also had the old Remington K models (two were on the shelf when I hired on) but the evaporator fans are actually bigger & move more air than the new cabinets.
    Unfortunately, the condenser louvre space (facing out of the building) was never considered when we bought the new cooling chassis. It's a private, non-profit hospital, so funds to purchase new, more open louvres is not going to be easy.
    If you could furnish more specifics on that fix, I would be very grateful.
    p.s.--I'm printing you post for my boss. This has not been a fun ride.

    ASCJ:

    I didn't realize I dropped the ball with you. The cooling chassis we have is a McQuay Model PKES1014CZ00Z00AR14A1A1. It slides thru the wall in a wall sleeve to outside louvres. Air is drawn from the floor, thru evap coils & out top via the evap motor.

  11. #11

    PTAC Condensate/Airflow issues

    Here is a report from another K installation, same "D" vintage units, high compressor failure rate, also some air flow issues.
    http://www.airdistributors.com/docs/...orproblems.pdf

    This report addresses the molex connector from the old unit to the adapter used to connect the new unit (829007731). Look for signs of loose fitting connections, arcing, etc. This can cause a brownout condition and kill a compressor.

    You mentioned you changed the room cabinet. Did you also change out the heat sections, or at least replace the coils and motors? This should help increase air flow. Regarding the outdoor louver, I've never run into that being a problem. One possibility, some installations I have seen screen material or hardware cloth used to keep out bugs, small critters, grass, debri, etc. If that's the case, you may want to consider removing it. You might want to try a new louver and see if it solves the problem. New louver part number is 105540501. Your local McQuay guy can get this for you, or I can supply.

    Peace,

    Greg McNary
    Air Distributors Company, Inc.
    airdistributors.com

  12. #12
    I failed to mention that the recommendations made in the report by McQuay solved the problem on this installation.

  13. #13
    McNary:
    Looked at the report. Those are the molex connectors that we had on the old units. With the new heating cabinets (new heat coils, blower, etc), we rewired all the units and replaced the old connectors. Would like to test the voltages thru the connectors, though. Thanks for your input. I'd like to talk with you one-on-one via e-mail or telephone more about what you found on this issue. It's opening new doors on this 4-year problem.

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