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  1. #1
    If the Demand Cooling is energised so much that ice is building up on the solenoid outlet ... does this mean the unit has an over temp problem?
    Possibly bad valves?
    I mean, it's not even hot here yet. It's only ninety something degrees. (F).


    Is there a way of testing those demand cooling systems?

  2. #2
    For the thermistor sensor: shut off control power.
    Resistance will be high if comp is cold (as high as 100,000). If warm, resistance is low (around 1800 is the lowest I've seen).

    For the module:

    Simulate low comp temp--Shut off control power and disconnect thermistor from the module. Turn on power again. There should be no voltage between "S" and "L2".
    Restore sensor and power.

    Simulate high temp--Careful because the injection valve will open if working properly so keep an eye.
    With control power off, jumper the points where the thermistor plugs in. Should read voltage at "S" and "L2" and injection valve should come on. After one minute it shoul trip because it's "sensing" high head temps (shorted thermistor). Now the output line from the injection valve sould be super cold. Shut off control power, remove jumper and reconnect sensor. Start comp as normal and that output line of the injection valve shoul start warming up (because the valve should be closed). If not, valve is bleeding by or check voltage at "S" and "L2". Should be none.

    I'm tired now.


  3. #3
    Join Date
    Sep 2001
    Location
    East Stroudsburg, PA
    Posts
    13,215
    Originally posted by R12rules
    If the Demand Cooling is energised so much that ice is building up on the solenoid outlet ... does this mean the unit has an over temp problem?
    Nope, it means the valve is working.

  4. #4
    Originally posted by condenseddave
    Originally posted by R12rules
    If the Demand Cooling is energised so much that ice is building up on the solenoid outlet ... does this mean the unit has an over temp problem?
    Nope, it means the valve is working.
    What range of temp does this valve operate at?

    Can I measure the temp at the discharge line or head, externally of course, and tell whether or not the demand should be calling?


    Thanks.

  5. #5
    Join Date
    Feb 2004
    Location
    Medford Oregon
    Posts
    807

    demand cooling

    Demand Cooling Operating Setpoints and Control Actions
    Internal Head Temperature Control Module Operation Sensor Resistance
    ************************************************** ***************************
    Rising through 292 F Demand Cooling Solenoid On 2100 Ohms
    Falling through 282 F Demand Cooling Solenoid Off 2400 Ohms
    Rising through 310 F Alarm Contact Energized 1700 Ohms
    At Room Temperature (77 F) Demand Cooling Solenoid Off 90,000 Ohms


    Check temperature 6 out on discharge valve
    If above 225 deg F, Demand cooling OK, but you have overheating problem
    If less than 225 and solenoid on, need to check sensor, modelule or solenoid

  6. #6
    Join Date
    Jan 2004
    Location
    Earth
    Posts
    4,879
    R-12 if you have a multi-head compressor, use your infrared thermometer to check your head temp on all heads. If one is much hotter than the others, this could be trouble.

    A internal blown head gasket on the head nearest the DC sensor could cause an overfeed. Your DC should cycle under normal operation. Demand cooling is a good thing, but it does eat into your capacity.
    A Diamond is just a piece of coal, that made good under pressure!

  7. #7
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,392

    Re: demand cooling

    Originally posted by rocket
    Check temperature 6 out on discharge valve
    If above 225 deg F, Demand cooling OK, but you have overheating problem
    If less than 225 and solenoid on, need to check sensor, module or solenoid
    I just got home from a call for a walk-in freezer down. It has a 2D( )-0600-TFC LT R22 with Demand Cooling so after getting the system back on line I checked the discharge temperature with a Fluke clamp on probe (as suggested about 6" after the discharge valve) and noted that the DC was cutting in at approximately 244 Deg F and out at 239 Deg F.

    From the DC temperature differentials stated, I would then expect the DC to trip at about 18 Deg above my CI point, or 262 Deg F, correct or no?

  8. #8
    Originally posted by R12rules
    If the Demand Cooling is energised so much that ice is building up on the solenoid outlet ... does this mean the unit has an over temp problem?
    Possibly bad valves?
    I mean, it's not even hot here yet. It's only ninety something degrees. (F).


    Is there a way of testing those demand cooling systems?
    All of the test proceedures have been discussed in great detail so I will not repeat.

    R-12, are you familiar with the pressure enthalpy curves? If so you can measure the actual suction pressure, suction temp at comp, and disch pressure. Plot those two points on the compression line and you will have a rough estimate at what the discharge gas temp is at the exist of the valves. It will really be higher because the compressor motor adds heat to the suction gas before compresson. This is what the demand cooling sensor is reading. The idea is to keep the disch gas temp below 280 so as to save the oil. R-22 is a strange beast for low temp. you want to keep the compression starting point real close to the saturation curve or the discharge temps go out of sight.

  9. #9
    Originally posted by R12rules
    If the Demand Cooling is energised so much that ice is building up on the solenoid outlet ... does this mean the unit has an over temp problem?

    might be........might not

    check that the good valve is install
    example: a valve for a 4D is not the same for a 3D, nor for a 2D....
    Don't interrupt me while i'm talking to myself

  10. #10
    this says because i saw the same symptom on a BRAND new compressor...the guys that replaced the compressor, replaced the valve and install a model for a 2D... on a 4D .....the result was ice accumulation on valve
    Don't interrupt me while i'm talking to myself

  11. #11
    2D valve has smaller orifice than the 4D valve so it can not keep up with the cooling demand and runs all the time. The ice comes from the fact that the liquid that is injected is boiling at suction pressure which is below freezing. Even the right size valve will ice if it runs for a long time.

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