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  1. #1

    Confused McQuay PTAC issues - help please!

    Hi -

    I have a McQuay Type K PTAC Unit that is less than 2 yrs old. When I tried using the AC this summer, the unit would not blow out cold air. The fan turned on but only blew out warm air. An HVAC company came to check out the unit and said the compressor wasn't working. They took the unit for repairs and diagnosed it as a defective expansion valve & weak compressor capacitor, both of which they proceeded to replace. When they brought the unit back to me, the compressor still would not start although they claimed that the unit was working when they had it in the shop. Now they are telling me it's a wiring issue inside the unit.

    Am I getting cheated here? Is there any way possible for the unit to be working in the shop but not working when they returned it to my apartment? Can a defective expansion valve or weak capacitor be diagnosed if the compressor was not working in the first place due to a wiring issue? What are some possible causes of a defective expansion valve or weak compressor capacitor?

    Any help would be appreciated! Thanks.

  2. #2
    Join Date
    Jan 2010
    A weak capacitor is easy to diagnose, you don't need the compressor running to do it. The only way I know to diagnose a bad expansion valve without the unit running is if there are parts broken (sensing bulb line, equalizer line, etc.), and that may be how they knew. Don't know for sure since I wasn't there. Odds are if there is a "wiring issue" it was caused when they were working on it or when it was being moved back to your place. Accidents happen, but if that is what happened they should fix it.

  3. #3
    Join Date
    Dec 2004
    Chicago area
    The only reason I can think that a unit will work in a shop, and not installed would be if there is inadequate power at the installed location.

    Meaning for example - 200 volts instead of 240 volts

  4. #4
    Join Date
    Mar 2009
    Southeastern US
    What kind of wiring issue? Bare wire grounding out? Wiring harness defective? Anything is possible, but if there is a wiring problem that was not there before it's logical to assume it might be a result of the previous work.

  5. #5
    I have the same type of PTAC and have a bit of bitter experience on them. Good machines, but wiring? My units have a plug in the end for a wiring harness. I've found the pins are sometimes melted (compressor shorted out) or bent through rough handling. Either case, compressor doesn't get the juice it needs to run. In my units, the power runs thru capacitor, thru freezestat to overload. Very little to go wrong. Capacitor, freezestat or compressor overload. All pretty easy to check out. I've yet to see a wiring harness defective.

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