Page 1 of 2 12 LastLast
Results 1 to 13 of 19
  1. #1
    Join Date
    Apr 2019
    Posts
    7
    Post Likes
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    AC unit starting twice.

    I was on a residential service call yesterday where the customer complained about the outdoor fan man motor not working sporadically. So I set the thermostat to several degrees cooler and go to check the unit out. Everything starts up outside this time but the fan motor is pulling high amps as suspected.

    Here's the weird part; about one to two minutes into running the unit shuts off, compressor and fan both just turn off. There's no way it reached the setpoint inside by now so I was scratching my head but after about maybe 20 seconds it turns back on and starts running again. I look over at the customer who happened to be standing nearby and he said the unit has always done that ever since it was installed. I thought maybe it was some kind of double start component I wasn't familiar with but after attempting to Google it I found nothing. The unit only shut off the one time and ran until it reached the setpoint after that initial restart and it did that same thing every single time. Anyone familiar with this? If it's not intentional the only thing I think it could be would be the thermostat.

  2. #2
    Join Date
    Jan 2010
    Posts
    19,339
    Post Likes
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    A model number would be nice

  3. #3
    Join Date
    Jan 2014
    Location
    New England
    Posts
    7,103
    Post Likes
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    What type of metering device does the unit have, piston or TXV. Maybe the unit is shutting off on LPC before the metering device has a chance to open. Does this unit have a LPC?

  4. Likes pageyjim, Metalman0880 liked this post.
  5. #4
    Join Date
    Jun 2017
    Location
    Missouri
    Posts
    220
    Post Likes
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    If the fan’s pulling high amps, is it possible the unit is going out on high head?


    Sent from my iPhone using Tapatalk

  6. #5
    Join Date
    Mar 2020
    Location
    Delaware
    Posts
    2
    Post Likes
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    It’s a good idea to have an HVAC company inspect your AC system for routine maintenance that you don’t have the skill or equipment to do, regardless of if you have an AC unit checklist or not.

  7. #6
    Join Date
    Dec 2006
    Location
    Vancouver, B.C.
    Posts
    1,001
    Post Likes
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    You really need to get your post count up and apply for pro membership. According to your last thread you should have been out of school for a year now. All that is asked is for you to interact with some technical posts to help us gauge what level your skill set is at. After 15 technical posts (not chit chat) then you can apply for professional status. It’s after that process is complete that we can really walk you though this. Until that happens you are going to get a lot of leading questions from people but the help you get will be limited depending on the information that you provide us.

    Why don’t you start by telling us what items you have checked so far, and what the operating temperatures and pressures were when you were checking them.

    At 1 year out of school you should not be running service calls by yourself. What does your journeyman think the issue is? Have you discussed this issue with any of your coworkers? What did they suggest?


    Sent from my iPhone using Tapatalk
    Quickly, I must hurry, for there go my people and I am their leader!

  8. #7
    Join Date
    Apr 2019
    Posts
    7
    Post Likes
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Thread Starter
    Sorry for the delayed reply have been at work all day. To answer your question no I'm not running service calls by myself. I was with a guy with 15+ yrs experience and he was also baffled by it. As far as I can tell the condenser fan motor had nothing to do with it, that just happened to be why we were there in the first place. The complaint from the customer was insufficient cooling and that the condenser fan motor was sometimes not running. We replaced the fan motor and put a little gas in the unit as it has a slow leak.

    After those fixes the unit ran great but it still had the weird double start issue. The customer wasn't concerned with it and didn't want us to pursue it further as he said it has always done that ever since installation and we were way behind on calls anyway. So I'm not really needing a walkthrough per say as the issue is resolved as far as we're concerned unless the customer calls back in the future. This is more just out of curiosity.

    The consistency of the double start almost made it seem intentional so I was wondering if anyone knew if there was a component that did that. It always started no problem, always ran for a set amount of time approximately 2 minutes or so and then shut down for 15 to 20 seconds before starting back up and then running continuously until it reached its setpoint. It seemed too deliberate to be a glitch. There was also a strange looking component inside the electrical compartment of the condenser that I haven't seen before that was wired up. Unfortunately I didn't think to take a picture at the time.

  9. #8
    Join Date
    Mar 2015
    Location
    Medford, N.Y.
    Posts
    6,946
    Post Likes
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    A brand & MN# would help instead of asking us to guess.

  10. #9
    Join Date
    Mar 2018
    Location
    Virginia
    Posts
    681
    Post Likes
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I can't see any reason why that would be intentional. It's not good for the compressor. It really reminds me of LPS (possibly HPS). You probably have a system that barely has enough charge. Initially it shuts down then as the refrigerant settles out it's able to run without LPS opening. Did you look at pressures?

    Sent from my SM-G960U using Tapatalk
    "Call a technician for God's sake. Or we'll see you on the news or the Dark Side of the Moon."

  11. #10
    Join Date
    Apr 2019
    Posts
    7
    Post Likes
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Thread Starter
    That seems plausible. We did find the unit slightly low on gas, about two pounds of R22 but I wonder if that would be enough to trip the LPS on a three ton unit in 100+ degree weather.

  12. #11
    Join Date
    Jan 2014
    Location
    New England
    Posts
    7,103
    Post Likes
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    To me 2 lbs is more than slightly low, could be 20-25%+- of the total charge on a 3 ton unit. Given that the suction pressure of R22 is somewhere around 65-75 PSI give or take and say the LPC opens at 12-15 PSI + - give or take to me that’s a small window.
    Last edited by Bazooka Joey; 05-05-2020 at 09:31 PM.

  13. Likes VTP99 liked this post.
  14. #12
    Join Date
    Oct 2011
    Location
    Culver, Oregon (Central OR)
    Posts
    2,818
    Post Likes
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Better than not starting.

  15. #13
    Join Date
    Mar 2018
    Location
    Virginia
    Posts
    681
    Post Likes
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Yeah 2lbs may be enough to cause low pressure issues (especially on a small unit). On start up the refrigerant hasn't yet reached an equilibrium so the suction can run low at first until it has time to come up. It's hard to say for sure but the most common reason an outdoor unit cycles like what you described is the LPS so that's the first thing I'd check.

    Sent from my SM-G960U using Tapatalk
    "Call a technician for God's sake. Or we'll see you on the news or the Dark Side of the Moon."

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •