Page 1 of 2 12 LastLast
Results 1 to 13 of 24

Thread: blast chillers

  1. #1
    Join Date
    Aug 2011
    Location
    Mn
    Posts
    12

    blast chillers

    I am back in the hvac industry after a very long time away. I am working on a blast chiller that runs 404A refrig. I have just changed out the old evap. for a new one. I pressure tested the new to 200lb with nitrogen over night. Today i put a vacumm in the thing and couldn't get it to pull any lower then 20" vac. I'm using a 7cfm 2 stage pump, and pulling though a 1/2 inch to 1/4 inch set of lines on my jb gauges. ? is what am I missing, if it held pressure, it should at least pull down I would think, even if it does have a leak someplace. This unit uses a copeland compressor, both rotovalves are fully back seated. I feel like i am missing something simple, but as yet my ahaa moment isn't forthcoming. Most of my previous hvac work was with comfort cooling, so maybe i just don't know enough. Help would be appreciated.

  2. #2
    Join Date
    Dec 2010
    Location
    Caretrsville Ga
    Posts
    24
    Quote Originally Posted by 85goldwing View Post
    I am back in the hvac industry after a very long time away. I am working on a blast chiller that runs 404A refrig. I have just changed out the old evap. for a new one. I pressure tested the new to 200lb with nitrogen over night. Today i put a vacumm in the thing and couldn't get it to pull any lower then 20" vac. I'm using a 7cfm 2 stage pump, and pulling though a 1/2 inch to 1/4 inch set of lines on my jb gauges. ? is what am I missing, if it held pressure, it should at least pull down I would think, even if it does have a leak someplace. This unit uses a copeland compressor, both rotovalves are fully back seated. I feel like i am missing something simple, but as yet my ahaa moment isn't forthcoming. Most of my previous hvac work was with comfort cooling, so maybe i just don't know enough. Help would be appreciated.
    Install an accurate micron guage it is possible that your low side guage is not reading properly

  3. #3
    Join Date
    Oct 2010
    Location
    Just East of West
    Posts
    29
    Did you hookup just your Gauge set and pull a vacuum on just the manifold set an see if it will pull to deep vacuum ... Gauge set could be leaky and causing you issues also your pump may be the problem, change the oil in the pump before you check the rest also make sure your micrometer is acurate as well..need a good micron gauge to ensure a tight system

  4. #4
    Join Date
    Aug 2011
    Location
    Mn
    Posts
    12

    i told you so

    Thanks for the replies gentlemen. I believe that I found the issue with my not being able to pull down to a good vacuum. By way of rechecking I hooked the set of gauges I am using up to the vacuum pump directly, with nothing else connected to any other hoses then the low side gauge. I was still not able to pull down into a good vacuum. I looked at the o-rings and it looked ok, but went and put another hose on it anyhow. Pulled right down into a good vacuum. I put the micron gauge on next, it pulled down to 30. This would be where you guys say "I told you so". New o-rings for the hose set tomorrow.

    Thanks guys.

  5. #5
    Join Date
    Feb 2008
    Location
    California
    Posts
    2,069
    they also make vacuum hoses or you can use soft copper with flares.

  6. #6
    Join Date
    Aug 2011
    Location
    Mn
    Posts
    12

    the plot thickens

    Well today I worked on my pet project and ran into a stumbling block. Hoses are fixed, vacuum is good. Used a brand new JB DV-40 micron gauge, pulled down to a 220 micron vacuum. It sat at this for about 30 minutes when i decided it was good enough. I added the 3.3 lbs. of 404a plus 2 more oz for consumption by the hoses. This thing has a good sized receiver so i wasn't to worried about going over a bit on the Freon. I checked for superheat about 8-10 inches from the txv before the evap. coil and about 3-5 inches from the suction return on the compressor. The book I have on this thing says about 20 degrees superheat is good. Now the problem. No matter where i set the adjustment screw for the txv. I can't get much of any chance on the superheat. So I asking to confirm my suspicion that the txv is bad. Let know what you all think. Other comments or ideas welcome as well

  7. #7
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,867

  8. #8
    Join Date
    Aug 2011
    Location
    Mn
    Posts
    12
    it didn't reach temp in either a chill 34 degrees or a freeze mode -10 degrees. it wouldn't go any lower then 48 degrees.

  9. #9
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,596
    What was the superheat readings?

  10. #10
    Join Date
    Aug 2011
    Location
    Mn
    Posts
    12
    suoerheat was 35 degrees

  11. #11
    Join Date
    Nov 2003
    Location
    Rochester, New York
    Posts
    392
    Still a bit low on charge I would say. Subcooling?

  12. #12
    Join Date
    Aug 2011
    Location
    Mn
    Posts
    12
    It is for sure not low on charge. I'm thinking that there is obstruction in one of the lines or the txv is bad?

  13. #13
    Join Date
    Dec 2008
    Location
    Dixiana, AL
    Posts
    2,611
    Post a complete set of readings and findings (such as "clear liquid line sight glass") and anything else you know about the operation even if you think it's not pertinent. Everyone is guessing.

    You also don't need to test superheat with a two thermometer set, 'cause you can't account for pressure drop in the evaporator. Do it with one thermometer and an accurate suction gauge w/ temp scale (or call jp and let him bring his digitals over so you don't have to do any cipherin' in your head).

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
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event