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  1. #1

    York Predator zf120

    I have been having a problem with York ZF120. Unit locks out on high pressure sporadically on both stages. Then just by resetting it the unit operates fine for a time and then for no apparent reason a repeat condition happens. Has anyone had the similar situation ? Thanks.

  2. #2
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    Are you the service technician, or the equipment owner?
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    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  3. #3
    I'm a technician

  4. #4
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    Could be locking out in high ambient. Maybe a fan motor is over heating.

    The ole' intermittant high head isnt isolated to that unit.

  5. #5
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    How about some more info.

    Condenser delta T?

    Superheat and subcooling?

    Estimated time of day when this happens?
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    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  6. #6
    Here's what happens... The first stage of cooling starts and trips the high head pressure control within 3-4 seconds. The unit is new. This locks out the unit and after restating sometimes it starts and runs for days. Then without apparent reason the situation reoccurs. It's charged with 410A. The York service representative has little input. Blames the situation on airflow. He says, York has no history with those symptoms with that model. We have jumped out the condenser fans to run as the unit starts. The blower runs as the the cooling begins. We have checked strainer, driers and changed expansion valves. I would think its something inside the condenser but the same thing happens to stage two as well. We have recovered refrigerant and recharged to manufactures nameplate specs. This happens whether it is 85* or 70*.... If you need more info..let me know..thanks. If this hasn't happened to someone.. It's difficult to troubleshoot since it has no history or normal diagnostic parameters.

  7. #7
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    I would place a tattle tale across the HPS to verify if they are opening, also check the ratings, maybe by mistake they installed r-22 safties, it happens.

  8. #8
    Thanks for your reply. We have verified the pressures are at the safety limits of 410A and the h/p switches are preset for 410A. Even if they were set for R-22 they would trip consistently, which is not the case. Sometimes the machine starts out normal and sometimes it shoots to cut out pressures within seconds. Because it doesn't happen every time, as soon as it operates normally... what is there to look for ? It has to be something within the manufacturing. I have thought of a pressure test plug within the piping and lodges itself whenever... But it happens to both stages at the same time after the compressor starts.

  9. #9
    Recover the charge.Scale back in minus 1 lb. per circuit and check superheat and subcooling.I would be curious of the outcome.(is this a Micro fin coil?)

  10. #10
    Yes sir, we have done exactly that. We thought factory overcharged. We subtracted refrigerant when recharged and it ran ok until it was cooler at night then locked out on freeze stat. Yes, it is a micro channel coil. We wonder if oil is slugging the condenser and simulating a restriction temporarily and when it clears the operation sustains. I don't know if the manufacturer specifies the amount of oil the compressors operate with or it is the compressor maker. Also, it's funny York has no input with the problem. I'm starting to believe oil is the problem. And now wonder if the unit trips after long off times and the oil migrates from the compressor into the condenser channels.

  11. #11
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    What is the pressure on your gauge when the HPS opens?

    What is the condenser delta T?

    What are your superheat and subcooling when it runs?
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  12. #12
    We are experiencing the same issue with the ZF120. We have narrowed our symptoms down to: When 2nd stage satisfies, the head pressure for stage 1 goes up to near or over the cut out of 650 momentarily and then slowly drops back down. Tech support had us install a time delay to hold the HPS in the circuit till the head drops back down. We tried this but we are still getting sporadic nuissance trips. We jumped stage 2 with stage 1 for the time being till we can resolve the issue. I try to grasp everything I can with thoughts of possibly with this micro-channel coil....stage 2 runs it's course, coil heated up, aluminum micro-channel coil expands, then when it shuts down it cools off and contracts to original thickness, allowing more air through stage 2 coil that is not needed, making stage 1 coil (that is still running) only getting say 80% of the airflow required, in turn increasing the head pressure. Just a thought. I will let you know what our resolve is hopefully by days end.

  13. #13
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    Quote Originally Posted by Hildy5652 View Post
    Here's what happens... The first stage of cooling starts and trips the high head pressure control within 3-4 seconds. The unit is new. This locks out the unit and after restating sometimes it starts and runs for days. Then without apparent reason the situation reoccurs. It's charged with 410A. The York service representative has little input. Blames the situation on airflow. He says, York has no history with those symptoms with that model. We have jumped out the condenser fans to run as the unit starts. The blower runs as the the cooling begins. We have checked strainer, driers and changed expansion valves. I would think its something inside the condenser but the same thing happens to stage two as well. We have recovered refrigerant and recharged to manufactures nameplate specs. This happens whether it is 85* or 70*.... If you need more info..let me know..thanks. If this hasn't happened to someone.. It's difficult to troubleshoot since it has no history or normal diagnostic parameters.
    Sounds electrical. Like the HP switches are rated for R22.

    If youve confirmed pressures then possibly fan motors not starting when compressor starts.

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