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  1. #1
    Join Date
    Jun 2013
    Location
    So. Cal
    Posts
    58

    Melted contactor, Lennox 6 ton rtu

    Lennox kha072s4bn1y

    Few days ago another tech went and checked this unit for no cool. Contactor was stuck open, he was able to bust it loose and unit worked, so replaced contactor and unit running. Today we got another call with same complaint, no cool. Space was 95* when I showed up. Check unit and same issue contactor stuck open. Other tech only had a 50 amp contactor on his truck so that's what he installed, OE is 40 amp. I changed out contactor and started unit up. Unit has not been maintained regularly so coils are packed with dirt and throw away filters are 8 lb bricks. Stabilized at 145 suction 425 discharge (R410A) 24* delta T (did not check SH). Unit pulling 22.5-22-18 amps and voltage is 194-195-192. Voltage is low but within the operating range of the unit (187-253). I pulled backing off of old contactor and the coil was black due to heat and melted plastic was keeping it from pulling in (50 amp contactor). 24v coil and transformer is putting out 25v. I did not check voltage at the coil unfortunately. Had calls stacking up behind me and had to split, what am I missing here? There's a twin to this unit about 15' away with same supply voltage and lack of maintenance but its purrin away whole time I was there.

  2. #2
    Join Date
    Jan 2005
    Location
    Houston TX
    Posts
    873
    Sounds like your 24 volt circuit is lower when low voltage controls energize, or try to depending on what low voltage controls you have installed on this unit. Indoor blower relay, condenser fan relay, duct smoke detector. If your line voltage was measured with the unit running check it with the unit off. If the unit was off with those voltage readings I hope you have a 200 volt unit. If it is 230-240 volt you are below the operating envelope 206-253. Your secondary under load would drop to 14-18 vac and coil would become an external heat source.
    Once in a while everything falls into place and I am able to move forward, most of the time it just falls all over the place and I can't go anywhere-GEO

  3. #3
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,509
    Did you clean the oils and install new filters?
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  4. #4
    Join Date
    Jun 2013
    Location
    N. Canada
    Posts
    368
    Quote Originally Posted by Aaronn View Post
    Lennox kha072s4bn1y

    Few days ago another tech went and checked this unit for no cool. Contactor was stuck open, he was able to bust it loose and unit worked, so replaced contactor and unit running. Today we got another call with same complaint, no cool. Space was 95* when I showed up. Check unit and same issue contactor stuck open. Other tech only had a 50 amp contactor on his truck so that's what he installed, OE is 40 amp. I changed out contactor and started unit up. Unit has not been maintained regularly so coils are packed with dirt and throw away filters are 8 lb bricks. Stabilized at 145 suction 425 discharge (R410A) 24* delta T (did not check SH). Unit pulling 22.5-22-18 amps and voltage is 194-195-192. Voltage is low but within the operating range of the unit (187-253). I pulled backing off of old contactor and the coil was black due to heat and melted plastic was keeping it from pulling in (50 amp contactor). 24v coil and transformer is putting out 25v. I did not check voltage at the coil unfortunately.........
    Yup, that's the word for it!
    Cking secondary voltage at the xmer is like checking your house acv at the power plant!

  5. #5
    Join Date
    Jun 2013
    Location
    So. Cal
    Posts
    58
    Customer has a company that changes their filters every six months, in a desert climate, with economizers. Tried to get them to wash the coils and change filters but the customer acted like I was trying to make up work to do. Using a ventstar t-stat. That voltage is with the unit running, and its barely within the spec on the unit tag. Unfortunately I know it's not fixed. Just band aid to get to the next job, scheduled to go back and continue to troubleshoot it. Biggest pain in the butt, 1.3 million sq ft warehouse and this unit is at the opposite corner of the building from the roof hatch, and parking is right bye the unit. So it's about 20 minutes round trip if I need something out of the truck.

  6. #6
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,509
    Is it possible the unit is short cycling or dropping voltage thru HPS because of the dirty coil or LPS because of the dirty filters and dirty coil? You can't properly diagnose the unit until the coil issues are resolved. You need to sell this idea to them. It will be cheaper for them in the long run.
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  7. #7
    Join Date
    Jun 2013
    Location
    N. Canada
    Posts
    368
    Quote Originally Posted by Aaronn View Post
    Customer has a company that changes their filters every six months, in a desert climate, with economizers. Tried to get them to wash the coils and change filters but the customer acted like I was trying to make up work to do. Using a ventstar t-stat. That voltage is with the unit running, and its barely within the spec on the unit tag. Unfortunately I know it's not fixed. Just band aid to get to the next job, scheduled to go back and continue to troubleshoot it. Biggest pain in the butt, 1.3 million sq ft warehouse ...................
    Wow ! Sounds like the aerodrome for the Spruce Goose!
    That being the case, I bet that there's a long stat wire run. If you see lo volts at the coil, you may have to add a relay & operate a 230v coil contactor from it. Amend schematic.

  8. #8
    Join Date
    Jun 2013
    Location
    So. Cal
    Posts
    58
    Tried to educate them about cleaning the coils and filters, how it will allow the unit to operate at maximum efficiency and save them energy and costly repairs in the future. But the facility manager was on repeat about its done every six months and corporate pays for it, other than that it comes out of her budget, which means she's getting paid a bonus at the end of year and if she doesn't spend a couple bucks on the AC units she gets a bigger bonus. My company has been trying to get a pm contract with them for a few months and they won't sign, until it gets to the point of a service call to reset hp lockout it won't happen. Hate it but you can't win them all. The unit is directly above the space and stat wire is run inside the return. Maybe 30' down and 30' back up. 18 gauge wire.

  9. #9
    Join Date
    Jun 2013
    Location
    So. Cal
    Posts
    58
    I watched it run for about 30 minutes continuously. Not cycling, and if it did trip on hp it locks out the comp, must be reset, and the stat is locked so it would generate a service call.

  10. #10
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,860
    1) I would make clear that each call is a cash call, no warranty if they choose to ignore the service advice. YOU control this relationship.

    2) Voltage range is for occasional power drops and surges, NOT continuous use. Your voltage is not acceptable. I'm going into Philly in a couple of mins to re-tap a power transformer for this exact issue, and then, you guessed it, I'm replacing the contactor that has low voltage burning it up...

    Only you can decide if this situation is too stressful or absurd. That is probably why you are there now: because others have given up on these guys. It is very likely that they did not plan for voltage drop when sizing the conductors that run to this unit, and when electricians ignore voltage drop, you can bet that they did not correct for high ambient conductor temps, either. Probably an in-house maintenance guy did it that "knows about electricity."

    If you choose to continue with this customer, document everything, and tell them that every previous call must be paid BEFORE another call will be accepted. That way, if they end the relationship by not paying an invoice, it is a smaller tuition payment in real life business school.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  11. #11
    Join Date
    Jun 2013
    Location
    So. Cal
    Posts
    58
    1) All I can do is report the facts to the customer, and my recommended work. Which is what I've done, and I documented on my invoice and with pictures the issues that I found.

    2) Low voltage was documented as a contributing cause of a burned out contactor. While it is within the manufacturers operating range it's dangerously close to minimum voltage and there may be unforeseen variables that cause it to drop below said minimum.

    Luckily they only have 2 maintenance guys and they stay away from electrical and hvac systems.

  12. #12
    Join Date
    Mar 2007
    Location
    South Texas
    Posts
    214
    Most pkg units have multi tap transformers 208 or 230. Make sure its tapped for 208 with the voltage you are reading. I normally see 26 or 27 when transformer is tapped properly.

  13. #13
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,860
    Quote Originally Posted by Aaronn View Post
    1) All I can do is report the facts to the customer, and my recommended work. Which is what I've done, and I documented on my invoice and with pictures the issues that I found.

    2) Low voltage was documented as a contributing cause of a burned out contactor. While it is within the manufacturers operating range it's dangerously close to minimum voltage and there may be unforeseen variables that cause it to drop below said minimum.

    Luckily they only have 2 maintenance guys and they stay away from electrical and hvac systems.
    It is my understanding that the minimum voltage for a unit is the voltage at which the unit can correctly operate during a drop due to brownouts, etc. You don't want to continuously operate a unit at the lower end of that range. For example there is no transformer tap for 193 volts, gents. You will have a chattering contactor and in continuous use, shortened the life of the compressor and motors, as well.

    If they don't want to replace the lines to the unit (taking a voltage drop AND conductor ambient into account, which trust me, would increase the size of those conductors by as much as three AWG sizes) they could have a buck-boost transformer installed at the unit, but I would recommend a competent electrician estimate the proper size conductors and install them according to code. Note: when using SE cable for a non-service entrance use, you must use the 60C column in the NEC to choose the size, and then adjust up for both the drop factor and the temp of the air where the conductors are being run.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







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