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What causes the suction line to freeze up periodically and has correct freon levels? The line freezes up maybe once a week. We have checked for leaks and there is no loss in freon.

  • By "correct freon levels" you mean that it's properly within the scope of the manufacturer's superheat or subcooling specifications? – Mazura May 19 '18 at 0:54
  • Hello, and welcome to Stack Exchange. What does "freeze up" mean? What do you do to end it? (I'm guessing the freon itself isn't going solid...) – Daniel Griscom May 19 '18 at 14:12
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The lines freeze when the cold air isn't being moved properly. This can be due to a few things, but the most common is low refrigerant. Dirty air filters, dirty coils, blocked or closed registers, blocked or closed returns can all contribute to low air flow, too, as can broken fan motors. You may not have noticed a leak in refrigerant, but did you have the pressure checked? It's likely that the pressure is low and refrigerant needs to be added. This is normally a closed system, so if some needs to be added, there is a leak somewhere - it may be a very small leak, but a leak nonetheless.

  • I have HVAC cert ive checked everything coils were cleaned and lines blown out last week! running 68psi/ 205psi – R.yarb May 18 '18 at 19:09
  • blowing 54-58 air out of all registers – R.yarb May 18 '18 at 19:11
  • If you have a certification you should know your suction line and liquid line pressures vary by type of Freon and that ambient tempatures. Those values mean nothing without the type & temps. – Ed Beal May 18 '18 at 19:13
  • THATS WHAT IM SAYING I HAVE ALSO HAD 4 OTHER TECHS LOOK AT THIS SYSTEM AND NO ONE CAN FIGURE IT OUT SO I THOUGHT I WOULD SEND IT OUT ON HERE BUT IM GETTING SAME THING WE HAVE ALL CHECKED!! EVEN CALLED CARRIER TECH SUPPORT!! – R.yarb May 18 '18 at 19:21
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    @R.yarb If it's that stubborn of a problem then what little information you provided is probably not enough to diagnose. The answer given here is a general answer to "why does any system leak?" not "given X setup, and the fact I've checked all (...) things what am I missing?". All caps aren't helping. – Brad May 18 '18 at 19:27
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Well Freon pressure can be misleading. If non compressables are in the lines (air) the pressures may look correct but be way out. Was a temperature probe used to verify the the vapor pressure at a specific temp? This alone can have a 100 psi variation in pressure. I use super heat, and sub cooling to see if the system is operating correctly, another note what type of gauge or line set was used to measure the pressure? Most untrained folks making this kind of measurement use a standard gauge / line set that releases an amount of the Freon where many pros use a gauge on a nipple so there is no real loss. Next after opening the system (making a measurement is opening the system according to the EPA) was the system leaked checked? Schrader valves are a main point of leakage if not properly sealed and checked after servicing. All this requires a license in the U.S. and most of the rest of the world so it is not really a DIY project. Did you know there are fines up to 25,000.$ for working on HVAC systems with out a licence.

  • I AM LICENSED HVAC TECH.. IVE BEEN WORKING ON SWYSTEMS FOR OVER 5 YEARS AND HAVE NEVER HAD OR SEEN THIS ISSUE.. NON OF THE OTHER LOCAL TECH CAN FIGURE IT OUT EITHER!!! I USE A FIELDPIECE DIGITAL MANIFOLD!! THERE IS NO LEAK IVE CHECKED IT WITH LEAK DETECTOR ALSO!! – R.yarb May 18 '18 at 19:18
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    As I said a line set waist Freon in the system, what Freon? R22, 134, 404, 410 are the main ones in use by using all caps (yelling) and not answering the critical information about temp maybe a real tech should be contacted, or go to a professional site like HVAC talk where real professionals discuss problems. Be prepared to answer the questions I brought up and do some reading online so you understand the importance of the measurements. – Ed Beal May 18 '18 at 19:27
  • sorry didn't mean all caps – R.yarb May 18 '18 at 20:00
  • r22 system there are no leaks to be found I ahev 200 unitn complex I work on these units daily!! – R.yarb May 18 '18 at 20:01
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    Beer can cold; you're too old. Superheat or subcooling, +1 – Mazura May 19 '18 at 0:56
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Things that will cause the suction line to freeze up:Low air flow, running the unit at a lower than recommended outside ambient, temperature too low in house, wrong refrigerant charge, worn out or bad restrictive device, miss matched indoor and outdoor unit.

  • IT ONLY FREEZES UP MAYBE ONCE A WEEK!! – R.yarb May 18 '18 at 19:21
  • That is probably because it is a little colder that day of the week and is bringing the real problem to light. It is right on the border of freezing the rest of the time. Lower outside temperatures lower the head pressure and that will lower the suction pressure causing ice formation. – user76730 May 19 '18 at 5:51

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