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  1. #14
    Join Date
    Jun 2009
    Location
    DFW, TX
    Posts
    642
    Quote Originally Posted by demidos89 View Post
    also for the head pressure does it have a fan cycling switch? it may need to be set to keep liquid going to the txv instead of hot gas.
    On a system without a headmaster, setting the fan cycle switch too low will NOT cause hot gas to bypass to the TXV. And on a system with a headmaster, the fan cycle switch is unnecessary if system is properly charged.

    Sounds to me like you have worked on some headmaster systems that were low on charge, so somebody added a fan cycle switch to try to keep pressure up rather than just charge the system properly. This may lead some people to believe that setting a fan cycle too low will cause hot gas to bypass to the TXV. However this is not true. The reason I am so passionate about this is I often see systems with headmasters, where somebody added a fan cycle switch, not realizing that the headmaster is a superior head pressure control device than a fan cycle control. Typically this is a "patch" for either a low on charge situation or a faulty headmaster valve. The solution is not to adjust fan cycle switch (or add a fan cycle switch) but rather to properly charge the system (or replace the faulty headmaster if that is the case).
    Last edited by trippintl0; 08-04-2013 at 03:11 PM. Reason: toned it down a little

  2. #15
    Join Date
    Nov 2009
    Location
    Richmond, working under tarps
    Posts
    482
    Quote Originally Posted by trippintl0 View Post
    On a system without a headmaster, setting the fan cycle switch too low will NOT cause hot gas to bypass to the TXV. And on a system with a headmaster, the fan cycle switch is unnecessary if system is properly charged.

    Sounds to me like you have worked on some headmaster systems that were low on charge, so somebody added a fan cycle switch to try to keep pressure up rather than just charge the system properly. This may lead some people to believe that setting a fan cycle too low will cause hot gas to bypass to the TXV. However this is not true. The reason I am so passionate about this is I often see systems with headmasters, where somebody added a fan cycle switch, not realizing that the headmaster is a superior head pressure control device than a fan cycle control. Typically this is a "patch" for either a low on charge situation or a faulty headmaster valve. The solution is not to adjust fan cycle switch (or add a fan cycle switch) but rather to properly charge the system (or replace the faulty headmaster if that is the case).
    As I agree with what you say........

    some equipment not designed for ambients below 60F are placed in environments seeing less than 60F ambients.

    Since the receiver is NOT sized for a extra charge to flood the condenser, fan cycle is one cheap option.

  3. #16
    Join Date
    Jun 2009
    Location
    DFW, TX
    Posts
    642
    Quote Originally Posted by indy2000 View Post
    As I agree with what you say........

    some equipment not designed for ambients below 60F are placed in environments seeing less than 60F ambients.

    Since the receiver is NOT sized for a extra charge to flood the condenser, fan cycle is one cheap option.

    I TOTALLY agree with you! On equipment not designed for low ambient, fan cycle is the cheapest most effective solution.

    But the lack of a fan cycle would not cause "hot gas" to flow to the TXV. I'm just trying to make sure demidos89 understands why he may have seen this happen - and it is because a headmaster is bypassing. Fan cycle is not capable of bypassing the condenser.

  4. #17
    Join Date
    Aug 2013
    Location
    Pennsylvania
    Posts
    50
    Much appreciated. The info I got lacked some theory. What you guys are saying makes sense. At first I was thinking for systems without recievers not sure if my theory would still apply to keep the proper level of subcooled liquid in the condenser preventing flash gas from getting to the metering device

  5. #18
    Join Date
    Nov 2009
    Location
    Richmond, working under tarps
    Posts
    482
    In theory, the condenser

    de-superheats
    condenses
    and subcools

  6. #19
    Join Date
    Nov 2009
    Location
    Richmond, working under tarps
    Posts
    482
    Quote Originally Posted by trippintl0 View Post
    But the lack of a fan cycle would not cause "hot gas" to flow to the TXV. I'm just trying to make sure demidos89 understands why he may have seen this happen - and it is because a headmaster is bypassing. Fan cycle is not capable of bypassing the condenser.
    agreed.

  7. #20
    Join Date
    May 2008
    Posts
    356
    I have not solved the problem yet. I have been overloaded with work. Temp is holding at 20. I went back Friday morning and adjusted the charge. The suction was 46. I managed to get it down to 36 and still keep a clear sight glass.
    If I go lower, I start getting bubbles. Temp dropped to 15. I had to leave and when I came back, temp was 20 again. I don't know how much traffic was in and out as it was a busy time of day when I checked. I will try to find a day this week to spend some time with it. The cond fan cycling switch is there but is not in the circuit. I don't know why it was disconnected. Defrost clock is working, heaters are working through the full defrost cycle (I didn't check the amps, but they are getting hot and defrosting nicely). I have to regroup and get you guys some fresh info, since I adjusted the charge down. Tonight I want to put something along the bottom of the door at closing time, where the seal is gone, and check temp first thing the next morning. It hasn't been long since I washed condensing coils - 2 months. But that's a good point, I can clean them with cleaner. I need another day to get my safety circuits/fan cycling wired in, gather some data (SH, pressures, temps). I will then repost. The txv is light gray. The condenser is check marked for 502 refrigerant. I dropped in 404A as I was told to do that by my predecessor. He said it wouldn't hurt. I feel if I can get this one right. Owners have had me on other projects, such as a new menu boards and recessed lighting, and he casually asked "is it possible to get the temp any lower". After adjusting the defrost clock, I seemed to eliminate the icing issue.
    td55

  8. #21
    Join Date
    Aug 2013
    Location
    Long Beach, Ca
    Posts
    16
    I'd be taking a look at that TXV to see if it's rated for 404A. We took over a McDonald's from another O/O and they were running 404 through the MAC6 and into a 502 TXV. I had nothing but problems until I got rid of it. (of course, the coil was an ancient McQuay, didn't help much either. evap coil fins looked like someone straightened them with a tennis racket.)

  9. #22
    Join Date
    Aug 2013
    Location
    Omaha
    Posts
    493
    Quote Originally Posted by tonydykes55 View Post
    I have not solved the problem yet. I have been overloaded with work. Temp is holding at 20. I went back Friday morning and adjusted the charge. The suction was 46. I managed to get it down to 36 and still keep a clear sight glass.
    If I go lower, I start getting bubbles. Temp dropped to 15. I had to leave and when I came back, temp was 20 again. I don't know how much traffic was in and out as it was a busy time of day when I checked. I will try to find a day this week to spend some time with it. The cond fan cycling switch is there but is not in the circuit. I don't know why it was disconnected. Defrost clock is working, heaters are working through the full defrost cycle (I didn't check the amps, but they are getting hot and defrosting nicely). I have to regroup and get you guys some fresh info, since I adjusted the charge down. Tonight I want to put something along the bottom of the door at closing time, where the seal is gone, and check temp first thing the next morning. It hasn't been long since I washed condensing coils - 2 months. But that's a good point, I can clean them with cleaner. I need another day to get my safety circuits/fan cycling wired in, gather some data (SH, pressures, temps). I will then repost. The txv is light gray. The condenser is check marked for 502 refrigerant. I dropped in 404A as I was told to do that by my predecessor. He said it wouldn't hurt. I feel if I can get this one right. Owners have had me on other projects, such as a new menu boards and recessed lighting, and he casually asked "is it possible to get the temp any lower". After adjusting the defrost clock, I seemed to eliminate the icing issue.
    For 404a I'd want the suction to be around 20 for a 0 degree box which is what the freezer should be rated for.

  10. #23
    Join Date
    Jun 2004
    Posts
    847
    So how did you adjust it to reduce suction pressures?
    So do you have mixed refer now.?
    The compressor still has mineral oil.?

  11. #24
    Join Date
    May 2009
    Location
    The Pas, Manitoba Canada
    Posts
    212
    Can the compressor pull into a vacuum with suction valve front seated? Try closing the liquid line valve to see what happens to the pressures this will imitate llsv operation. The compressor head valves or headmaster might be doing weird things.

  12. #25
    Join Date
    May 2008
    Posts
    356
    I know this thread is long overdue. I have not been back on this site for a few months. I was to the point of evacuating, changing the txv, and weighing in a new charge -
    as a last ditch effort. this evaporator and condenser is looks like they were drug out of the scrap yard, so we were looking at replacing the system. However, the last thing I
    did was clean the cond coils with cleaner and the next day we were at 0-5 degrees. It has been 5 months or more with no problems. So I have learned a great deal about freezers
    on this old beat up piece of equip. I've since fixed a few more. I am no longer intimidated by freezers or coolers. I have made a ton of mistakes, done stupid things I am not
    proud of and I have paid the price. today, I try to fix it right the first time. I need to start reading threads again. This site is invaluable to me. Thanks for everyone's feedback!
    td55

  13. #26
    Join Date
    Aug 2013
    Location
    Omaha
    Posts
    493
    So next time you'll clean the condenser first right?

    Sent from my XT1060 using Tapatalk

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