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  1. #27
    Join Date
    Mar 2007
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    wedged in freezer shelf
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    6,146
    Quote Originally Posted by yotaman16 View Post
    If you front seat the suction the unit will pump down and if the pressure rises your valves in the compressor are bad
    or bad suction service valve or refrigerant in the oil
    “If You Can Dodge A Wrench You Can Dodge A Ball”

  2. #28
    Join Date
    Jan 2006
    Posts
    1,120
    I would stick a good ole fan cycle on the unit and run the head pressure up to around 240 before the fan came on,doesnt take long and worth a shot.Also check and see if ya are haven some defrost problems,most walk in coolers have a defrost timer,if it doesnt you can set your pressure control to cut the unit of when freezing up if thats the case,theres lot of stuff you can check and so on.One way you could've checked the compressor is to undo the fan motor and c how long it takes to pump up some high pressure,shouldnt take long at all,with all the refrigerant you added to it.Check your amp draw also when your putten the compressor under stress,it should be pulling pretty close to the fla when unplugging a fan motor and running that head pressure.
    There are three signs of old age.
    The first is your loss of memory,
    the other two I forget.


  3. #29
    Join Date
    Jan 2007
    Location
    maine
    Posts
    787
    What happened to the old saying dont use fan cycle controls on a semi

  4. #30
    Join Date
    Jan 2007
    Location
    maine
    Posts
    787
    Quote Originally Posted by itsiceman View Post
    or bad suction service valve or refrigerant in the oil
    thos would affect it too.. Odds r the suction valve isnt bad tho.. But thats why i use the performance cure too

  5. #31
    Join Date
    Jun 2005
    Location
    Las Vegas NV
    Posts
    1,139
    Quote Originally Posted by yotaman16 View Post
    What happened to the old saying dont use fan cycle controls on a semi
    You are correct. Air cooled semi's require air to cool them The condenser fan is normally enough. If the second character of a Copeland semi is an "A" then it's air cooled. Second letter "R" or "D" then it's refrigerant cooled and only needs air cooling at certain low temp conditions.

  6. #32
    Join Date
    Jan 2007
    Location
    maine
    Posts
    787
    Quote Originally Posted by powell View Post
    You are correct. Air cooled semi's require air to cool them The condenser fan is normally enough. If the second character of a Copeland semi is an "A" then it's air cooled. Second letter "R" or "D" then it's refrigerant cooled and only needs air cooling at certain low temp conditions.


    Thats good to know.. I never knew that but there are a few units at stores i service that use fan cycle controls on them and i always said the first call i do on the unit they will come off but i will check that before i do.. Thanks

  7. #33
    I don't want to over-step on my very first post, but you guys seem to be going all out on this. Information is good, and I agree with all of you. Not to beat a dead horse, but put a head pressure control on the thing. If your temp is dropping because of the air being forced accrossed the coil your pressures are going to drop also. Stop the fan and you will raise the head pressure. As far as the off cycle and the suction pressure. If the pressure is rasing after you pump down you are leaking through somewhere, 9 times out of 10 it is at the solinoid coil.

  8. #34
    Join Date
    Feb 2004
    Location
    Medford Oregon
    Posts
    807
    "You are correct. Air cooled semi's require air to cool them "

    fan control used on air cooled condensor, on some semi air cooled models the condensor fan is also used to cool compressor (dual use). so adjusting fan control may hurt compressor. On refrig cooled compressors the condensor fan is used only as condensor fan.(not related to compressor)

    all welded compressors are refrig cooled! (compressor don;t care about fan control)

  9. #35
    Join Date
    Sep 2006
    Location
    Chicago
    Posts
    474
    This one bit me in the ass today. Yesterday I left and unit was down to temp today I get called over at 5:30 pm to work on it. Was very busy today with heat calls. I knew at this point that I wasnt gonna have any parts and everyones closed for the weekend. Lesson learned should have done it all yesterday. Just kinda sucks with the king valve leaking but not to big a deal i guess. So basically today I went back to do more diagnostic work for monday.

    Units pressure was still the same as yesterday but superheat was 43 degrees so obviously it wasnt cooling. Suction is still around 21#.Since Refrigerant dumping dosent seem to affect this system as i learned yesterday I decided to not do that today instead I focused on actually diagnosing it cause fixin its the only way to move on for me.

    Kind of like you guys said I could disconnect the fan and check pressures. I decided to put my coat over the condenser and it rose well above 200 psi in a short amount of time. But even after all this it didnt change suction pressure an ounce. Right now Im thinking TXV. I mean a system thats 52 degrees should really have a high suction to begin with. So even if it was 90 degrees outside instead of 15 the suction would be low.

    System has always had a clear sight glass as I mentioned earlier.

    Another strange occurence I noticed was the system pumping down occasionally??? Ok so this cooler is 15 degrees to warm. Its not smart enough to tell itself Im sucking time to shut er down. And after awile the selenoid opens again. I know the valve was closing cause it pumped down then a little while later I could see the line shake when it comes back on after the predetermined time on the thermostat.

    As I said this system has no defrost clock just off cycle.

    And then I go to look at the TXV valve bulb and every thing around it like the insullation and such are either totally covered in oil or leak detectent soap bubbles. Almost seamed and smelled more like oil to me. Very strange snooped all around system with my leak detector and picked up nothing. Would have assumed major leak but I guess not.

    Also it dawned on me wouldnt you get a metering effect at the selenoid valve if it was leaking on off cycle?

    So many thoughts so little time to straighten them out. Im experienceing these long days everyone spoke of on here. After fixing alot of stuff this week sucks to end it on a bad note like this. You guys are great though and give hope. Thanks, Dan

  10. #36
    Quote Originally Posted by rocket View Post
    "You are correct. Air cooled semi's require air to cool them "

    fan control used on air cooled condensor, on some semi air cooled models the condensor fan is also used to cool compressor (dual use). so adjusting fan control may hurt compressor. On refrig cooled compressors the condensor fan is used only as condensor fan.(not related to compressor)

    all welded compressors are refrig cooled! (compressor don;t care about fan control)
    So you are telling me that you have never seen a welded compressor over heat and trip on internal overload after the condenser fan motor has gone bad?
    Last edited by Joe Subcool; 11-30-2007 at 10:02 PM. Reason: want to stress welded

  11. #37
    what I am trying to say is that any component in a refrigeration unit will affect the compressor no matter what its use is. you mess with the fan, you mess with the refrigerant pressures which in turn affects the compressor. Fan cycling control is very important to a unit that is outside and ran all year or in a refrigerated space. The cold temps will lower the pressures in the system to low for it to operate, just like the low suction and head presures here. If the ambinet temp is low you may not need the fan at all.

  12. #38
    Join Date
    Jan 2006
    Posts
    1,120
    I would look at the sight glass but not really pay a whole heck of a lot of attention to it,I think from what Ive brushed up on here on hvac talk most seasoned techs say that the sight glass works pretty well for charging if your at full load conditions.With it being 20 outside and 50 in the box that is a far cry from full load IMO.Now it being a air cooled compressor would maybe cause promblems in the summer,but I don't think a little raise in head pressure is gonna hurt,with cycling the fan and all,JMO.Have ya tried setting the pressure control a little lower,at what suction pressure is the unit cutting of on,just a thought,Ide do what I had to,gotta get the temp of that box down there,your job depends on it
    There are three signs of old age.
    The first is your loss of memory,
    the other two I forget.


  13. #39
    Join Date
    Sep 2006
    Location
    Chicago
    Posts
    474
    Unit has low suction pressure but its not cutting off. It was cutting off on the off cycle on pump down like it should it was just raising pressure and cycling. High even cut it is at 20 and differential is at 15 so it cuts out at 5psi. Theres something else going on here.

    Monday I was gonna recover charge to see how much is in the system cause I may still have a leak somewhere. Then pressurize with nitrogen. Change TXV and LLS,filter. Triple Vac and recharge. No matter what I do to head or charge suction remains constantly low. And yesterday superheat was high. It was to late on a friday to get parts so I was screwed.

    Wouldnt the site glass show bubbles though if you were low on charge even in winter. So basically I simulated summer like conditions on the condenser by blocking it off right? I would think that if you didnt have enough refrigerant to flood the condenser and supply a full liquid column the glass would be flashing wouldnt it.

    Like I said king valve is shot so there goes pumping down for repair.

    Dosent matter now anyway it got taken away from me cause there banking on someone to have parts. Same thing happened last friday. Had a system with a leak in the evap said I couldnt get parts for the weekend they called somone else saturday morning and they said the same thing and they got the job from me.
    Last edited by dangpgt97; 12-01-2007 at 10:26 AM.

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