Results 1 to 5 of 5
  1. #1
    Join Date
    Nov 2004
    N. Texas
    Most service calls, I don't need to refer to schematics. I can usually look and see. Even in units that have control PCB's. Today I made a service call on a 8 yr old Lennox that did not have 24vac to the coil. I traced the 24v wire from the incomming lug to the contactor. It went thru several wizzbangs before it made it to the contactor. Although I have serviced this unit this year, I have never taken the time to look at the wiring. There is a lot of crap. I just figured it was a HP so extra wiring was normal.

    The schematic looked like it was drawn by a child. Labels were on part of it and missing from other parts. I am very good at reading schematics, and have read schematics from hell. Written in Italian with new names from page to page, and with alternate pages in English. I also have experience with same color wires. machines wired all in black or white wire.

    This schematic was from hell. It could not be understood. Names were on 1/2 of the pictorial(if you can call a crappy drawing with no correlation to the schematic a pictorial) and missing names on the rest of the drawing. The equipment has a P&B relay, with several contacts not defined. It has another relay undefined that is using 3 contacts of 4. It also has a high pressure switch connected to a port on the acculumator with a reset button.

    The schematic does not define the reset button or how it is wired into the circuit, It has a name for the reset but does not use the identifer "RESET" anywhere.

    I pressed the reset, and the system reset itself and started to work. The whole process took about 30 minutes in the sun.

    Since the unit belongs to my boss, I cleaned up and went home to research the problem. Any suggestions?

  2. #2
    Join Date
    Jul 2005
    north carolina
    well it sounds to me like you may be working on a chp20 lennox php? if so there are 2 pressure switches in the low voltage.1 is for defrost termination and the other is standard pressure switch.there is a few things that will cause a trip on the chp..

    1....dft t stat bad sending voltage to defrost board motor or cap
    3.... dirty cond coil
    4....or weak pressure switch
    or the last tech didn't have a clue what he was doing and replaced wrong switch and wired it in series with the manual reset pressure switch!!! which will take you a while to find if not knowing ( been there took 30 minutes to find)that the guy did it.

    1 thru 5 is in cool mode

  3. #3
    Join Date
    Jul 2005
    North Central Ontario Canada


    we used to call some of the lennox schematics from a few years back pretend diagrams as they were their own interpretation between a ladder diagram and a pictorial.

    i attended a factory trainning course with one of the desginers of the pulse unit and when he sat there in front of you and described the sequence of operation you could kinda follow along on that diagram. thats how it was based.

    it is possible the condensor fan motor is starting intermittently causing the lockout..weak coil or contacts on relay. some relays were integral to a pcb.

    i dont miss working on the early nineties york rooftop units with all white control wiring with black numbers printed on them that fadded away. frustrating.
    Here's your sign...

  4. #4
    Join Date
    Nov 2001
    An 8 yr old h/p isn't like the old hp-8 or hp9's.

    The h/p wiring in the cooling mode doesn't include all of the system wires. only look at the cooling circuit.

    whats the model and serial and size.

    If you try to fail, and succeed.
    Which have you done ?

  5. #5
    Join Date
    Nov 2001
    east kansas
    I have a hard time following their commercial drawings.

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