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  1. #1
    Join Date
    May 2011
    Location
    San Antonio, TX
    Posts
    34

    High Side Low, Low Side Low

    La Rosa Ice Cream Dipping Station struggling to hold temperature.

    I cleaned the condensor coil (filthy) with nubrite and painted with coil paint.
    Recovered refrigerant, pressure tested to 150psi, left overnight. Pressure dropped 1psi,
    but ambient temperature dropped almost 30F too, so I figured that's within the limits.
    Triple evacuated down to 300 microns on the last pull and I metered in 10oz virgin r134a
    per the info plate.

    information plate:
    L-14246
    refrigerant: r134a, 10oz
    150/ Low side psig
    335/ High side psig

    Readings:
    ~0psi on suction line next to compressor
    no refrigerant valve on the high side
    128F compressor discharge which corresponds to 193psig
    ~32F evaporator discharge - frost is forming on the pipe,
    but my infrared thermometer reads 40F (?)

    So, it seems that high side pressure is low and the low side pressure is low.
    I originally thought the capillary tube might be plugged, but I would expect
    higher pressure on the high side. Right?

    I'm thinking the compressor is shot. Does anyone have any thoughts on something else I should check before replacing the compressor?

    Would checking the amperage draw on the compressor tell me anything?

    BTW, I am a noob, but I am EPA & Texas licensed (universal).

    Thanks much!
    Last edited by clearchris; 06-10-2011 at 12:51 PM. Reason: added info

  2. #2
    Join Date
    May 2004
    Posts
    12,230
    Couple of things. You should have installed an access fitting on the high side when you had the chance, even if you simply installed a new CAPT-032 Sporlan drier. They have an access fitting built in. Make sure your captube is pointed downhill out of the drier for a liquid seal. (note, when adding a CAPT-032s you must compensate with 1 extra oz of refrigerant.)

    Next, did you think of compensating for the amount of liquid in your gauge hoses for the 10 oz weight? It could be undercharged by 1 or more ounces which is 10% or more.

    An infrared gun will not give accurate line temps to correspond to temperature.

    With the info you have I don't think the compressor is shot. The info plate showing the pressures are "maximum tested limits" and are not running pressures. If your weight is correct then I would suspect blocked captube and/or spun drier.

  3. #3
    Join Date
    Mar 2011
    Location
    Texas
    Posts
    27
    The suction being 0 psi tells me your compressor is pumping. If you compensated your charge for your gauge hoses and the new drier, the cap tube or drier might be stopped up. You might try to add a couple more ounces of freon and see if that helps.

  4. #4
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,870
    As a "rule of thumb" 1/4" service hoses hold 1 ounce of liquid per 3 feet.

    Vapor hoses hold significantly less.

    I hate seeing r134a as a low temp refrigerant.

    Good luck.

  5. #5
    Join Date
    May 2011
    Location
    San Antonio, TX
    Posts
    34
    Quote Originally Posted by Lusker View Post
    Couple of things. You should have installed an access fitting on the high side when you had the chance, even if you simply installed a new CAPT-032 Sporlan drier. They have an access fitting built in. Make sure your captube is pointed downhill out of the drier for a liquid seal. (note, when adding a CAPT-032s you must compensate with 1 extra oz of refrigerant.)

    Next, did you think of compensating for the amount of liquid in your gauge hoses for the 10 oz weight? It could be undercharged by 1 or more ounces which is 10% or more.

    An infrared gun will not give accurate line temps to correspond to temperature.

    With the info you have I don't think the compressor is shot. The info plate showing the pressures are "maximum tested limits" and are not running pressures. If your weight is correct then I would suspect blocked captube and/or spun drier.
    I like the idea of the CAPT-032s. I didn't add one because I couldn't get the flare fitting off, have any tricks for that? Should I hit it with a torch to heat it up and loosen it? If it weren't refrigeration, I would use PB Blaster on it, but I didn't want to contaminate the system.

    I charged vapor. First I pulled a vacuum on the hose, then I filled the hose with refrigerant before hitting tare on the scale. I believe that since the hose was full when I started charging, and it was full when I finished charging, it should net out. It was one 3" long, 1/4 diameter hose.

    What type of thermometer would you recommend? Thermocouple with a pipe clamp attachment?

    If the pressures on the info plate are max working temperatures, how does one determine what the pressures should be?

    Thanks again!

  6. #6
    Join Date
    May 2004
    Posts
    12,230
    Quote Originally Posted by clearchris View Post
    I like the idea of the CAPT-032s. I didn't add one because I couldn't get the flare fitting off, have any tricks for that? Should I hit it with a torch to heat it up and loosen it? If it weren't refrigeration, I would use PB Blaster on it, but I didn't want to contaminate the system.

    I charged vapor. First I pulled a vacuum on the hose, then I filled the hose with refrigerant before hitting tare on the scale. I believe that since the hose was full when I started charging, and it was full when I finished charging, it should net out. It was one 3" long, 1/4 diameter hose.

    What type of thermometer would you recommend? Thermocouple with a pipe clamp attachment?

    If the pressures on the info plate are max working temperatures, how does one determine what the pressures should be?

    Thanks again!
    Here's what I would do but it going to cost you labor already preformed.

    Use tubing cutters to remove the old drier. Hook up your nitrogen bottle and blow about 250 lbs of pressure though the captube while leaving the suction valve open. Sweat in a CAPT-032s. Pull another vacuum. Weigh the charge via vapor and let settle (warm up and equalize). Add 1 oz extra for the CAPT-032s. When it equalizes start the system and watch the suction line. Make sure the drier is pointed down so there is a liquid seal at the exit end of the dryer.

    The only problem I believe you to have is undercharge by an ounce or two if the captube is clear but any time you open a system you should replace the drier, spun type or not.

    Use a multimeter with a temp clamp, thermocouple type is correct. There is no need to use one here though.

    There are no "perfect" pressures to look for here. It all depends on sizing and box temp. Call the factory and ask them but you aren't going to get your correct pressures until the box is just about to temp. Cold plates can take a long time to give you correct operating pressures but you will see a frost line.

  7. #7
    Join Date
    Jun 2006
    Posts
    1,105
    Quote Originally Posted by clearchris View Post
    Readings:

    128F compressor discharge which corresponds to 193psig

    but my infrared thermometer reads 40F (?)


    Would checking the amperage draw on the compressor tell me anything?
    No disrespect intended.

    Highly superheated vapor temps on the hot gas / discharge temps do not correspond to the pressure temperature relationship at saturation. Significantly more information would be required to predict the SCT with any level of accuracy, your 193 guess is not to be considered close, nor is the infrared reading, they do not cut it for the industry despite marketing hype.

    The compressor amperage would indeed give you some insight if compared to the RLA to determine if the unit was performing near capacity. Unfortunately it is not the end all answer, it is just not that simple.

    You have not provided enough information to determine a lot and not enough to offer much assistance beyond guessing.

    You cleaned a really dirty condenser, you likely have close to the right charge, but that is also open to question to a degree, you are working on a machine with little tolerance for mistakes and you are going to need to approach it differently if you are going to solve the problem and make an accurate diagnosis.

    Weak compressor, real possibility, but no signs of it from info provided.

  8. #8
    Join Date
    Jul 2008
    Posts
    440
    Quote Originally Posted by jpsmith1cm View Post

    I hate seeing r134a as a low temp refrigerant.
    .
    Why's that? Just curious
    "It's just like it doesn't work. I mean it seems to be ok now, but it usually like never works"

    "Never an always and always a maybe"

  9. #9
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,870
    Quote Originally Posted by dave1234 View Post
    Why's that? Just curious
    The low side pressures are too close to atmospheric for my liking. Too much of a chance of drawing in contaminants.


    Clearchris,

    Do you understand HOW a refrigeration system works? Do you know what the term saturation temperature means?

    If not, my friend, we're reaching stage. Call a qualified tech out to help you in completing these repairs.

  10. #10
    Join Date
    May 2011
    Location
    San Antonio, TX
    Posts
    34
    Quote Originally Posted by Lusker View Post
    Here's what I would do but it going to cost you labor already preformed.

    Use tubing cutters to remove the old drier. Hook up your nitrogen bottle and blow about 250 lbs of pressure though the captube while leaving the suction valve open. Sweat in a CAPT-032s. Pull another vacuum. Weigh the charge via vapor and let settle (warm up and equalize). Add 1 oz extra for the CAPT-032s. When it equalizes start the system and watch the suction line. Make sure the drier is pointed down so there is a liquid seal at the exit end of the dryer.

    The only problem I believe you to have is undercharge by an ounce or two if the captube is clear but any time you open a system you should replace the drier, spun type or not.

    Use a multimeter with a temp clamp, thermocouple type is correct. There is no need to use one here though.

    There are no "perfect" pressures to look for here. It all depends on sizing and box temp. Call the factory and ask them but you aren't going to get your correct pressures until the box is just about to temp. Cold plates can take a long time to give you correct operating pressures but you will see a frost line.
    I understood that capillary tube (critical charge) systems were a risk of slugging the compressor if there's too much refrigerant. How much is that generally? There's three coils in the suction line before it returns to the compressor, would those help trap any liquid?

  11. #11
    Join Date
    May 2004
    Posts
    12,230
    Quote Originally Posted by clearchris View Post
    I understood that capillary tube (critical charge) systems were a risk of slugging the compressor if there's too much refrigerant. How much is that generally? There's three coils in the suction line before it returns to the compressor, would those help trap any liquid?
    It may trap a little oil but doubtful it will trap refrigerant in a gas state. You can't worry about the manufactures design. Don't try to re-engineer or over think this simple box.

    Overcharging a critical system will depend on the system. Add your weight, wait for results. Add an oz, wait for results. I would not add more than 2 oz unless you go with a CAPT dryer. The CAPT-032s drier will act like a very small receiver as long as you keep a liquid seal on the captube entrance.

  12. #12
    Join Date
    Jan 2010
    Posts
    6,622
    I would guess your low side should be at about 4psig. Which would give you about a -5* cold wall.
    How old is that equipment ? Got a serial # ?

  13. #13
    Join Date
    Jan 2006
    Location
    Near Atlanta, GA.
    Posts
    14,587
    Quote Originally Posted by jpsmith1cm View Post
    The low side pressures are too close to atmospheric for my liking. Too much of a chance of drawing in contaminants.

    And it's capacity at that low of an evap temp is not that great.

    Of course, I really don't like 134a for much of anything. I thonk we'll see it go away in a few years.

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