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  1. #27
    Join Date
    Jun 2010
    Location
    U.A. (upper Alabama)
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    874
    Quote Originally Posted by ga1279 View Post
    The sensors themselves can be way out of wack and not cause an alarm, if you suspect this, then you should pull the sensors out and let them sit in a cold water bath[/U] along with an accurate thermometer. These sensors are in the refrigerant flow so you have to pump the evaporator refrigerant from the king valve to the compressor into the condenser and if you not sure of yourself doing this find someone who knows this procedure.
    ?

  2. #28
    Join Date
    Mar 2011
    Location
    Abilene Tx
    Posts
    82
    Yea, probably not a good idea to put them in water. With the chiller off, temps should stay steady enough to ohm out sensors. Just leaving the sensors in the system will be good.

  3. #29
    Join Date
    Jul 2007
    Location
    The Hot South
    Posts
    1,373
    I agree that the sensors should not be put in water unless you want to introduce moisture into the chiller.

    There is no reason the chiller can't be pumped down to replace the sensors. Hook up your gauges and have your hand on the disconnect and make sure it doesn't go into a vacuum. It is not necessary to pull the entire charge just to change the sensors. Pump it down to 20 PSI and change them on the fly.

  4. #30
    Join Date
    Mar 2011
    Location
    Abilene Tx
    Posts
    82
    Yea, just expect to get sprayed with oil if you are gonna pull out the compressor suction sensor with 20 psi left in there! I just ain't that quick! Lol

  5. #31
    Join Date
    Jul 2007
    Location
    The Hot South
    Posts
    1,373
    You could also pump the residual gas over to the condenser with a recovery unit.

  6. #32
    Join Date
    Mar 2007
    Posts
    3,140
    I have replaced a lot of RTAA suction temp. sensors and have yet to get sprayed with oil. Not saying it can't happen, but hasn't happened to me yet.
    The key to happiness is lower expectations.

  7. #33
    Join Date
    Mar 2011
    Location
    Abilene Tx
    Posts
    82
    Quote Originally Posted by BergerMech Rob View Post
    I have replaced a lot of RTAA suction temp. sensors and have yet to get sprayed with oil. Not saying it can't happen, but hasn't happened to me yet.
    You got me curious. I usually just isolate the compressor and recover residual then take it out. But I am pretty sure I have always had oil come out steadily. If there ain't some oil that comes out I would be worried. You are talking about comp suction temp sensor and not the sat evap temp sensor?

  8. #34
    Join Date
    Jan 2005
    Location
    Houston TX
    Posts
    880

    Refrigerant sensors

    Cowpoke- I generally leave just a little (2-4) pounds of pressure and have a new sensor already made up (compression ring on the sensor) so I can pull the old sensor out and push the new sensor in. I mark the position of the holes in the sensor tip so I can align them on installation. I keep a blank sensor to use as a plug if I just want to check temperature calibration. I have never gotten an oil bath during this process. I want to always leave the refrigerant side positive as oil out is a lot better then air and moisture in, can I get an Amen on that.-Geo
    Once in a while everything falls into place and I am able to move forward, most of the time it just falls all over the place and I can't go anywhere-GEO

  9. #35
    Join Date
    Oct 2003
    Location
    tidewater, va
    Posts
    2,147
    Had an exv stick open on me on a 70 ton like this, obviously stuck open with lukewarm discharge temp. Went out on oil fault. Chnged exv and all worked well.

    r404a

  10. #36
    Join Date
    Mar 2011
    Location
    Abilene Tx
    Posts
    82
    Quote Originally Posted by ga1279 View Post
    Cowpoke- I generally leave just a little (2-4) pounds of pressure and have a new sensor already made up (compression ring on the sensor) so I can pull the old sensor out and push the new sensor in. I mark the position of the holes in the sensor tip so I can align them on installation. I keep a blank sensor to use as a plug if I just want to check temperature calibration. I have never gotten an oil bath during this process. I want to always leave the refrigerant side positive as oil out is a lot better then air and moisture in, can I get an Amen on that.-Geo
    AMEN!

  11. #37
    Join Date
    Mar 2007
    Posts
    3,140
    Quote Originally Posted by r404a View Post
    Had an exv stick open on me on a 70 ton like this, obviously stuck open with lukewarm discharge temp. Went out on oil fault. Chnged exv and all worked well.

    r404a
    Discharge superheat and discharge temperature always tells the tale with these and most screw machines.
    The key to happiness is lower expectations.

  12. #38
    Join Date
    Mar 2004
    Location
    ottawa canada
    Posts
    2,111
    My vote is a bad sensor. Shut it down and wait. The two sensors should read pretty close. If they dont, replace. When they fail they usually read way off before they open or short.

    This is correct

    The sensors themselves can be way out of wack and not cause an alarm, if you suspect this, then you should pull the sensors out and let them sit in a cold water bath along with an accurate thermometer.

    This idea is out to lunch !!!

    There is no reason the chiller can't be pumped down to replace the sensors. Hook up your gauges and have your hand on the disconnect and make sure it doesn't go into a vacuum. It is not necessary to pull the entire charge just to change the sensors. Pump it down to 20 PSI and change them on the fly.

    The RTAA is designed in such a way as all the refrigerant can be transferred to either the high or low side as required to perform service . Use the pumpdown feature and with gauges on the chiller and one hand ready to remove the control fuse or remove the emergency stop jumper and install a toggle switch (PULLING DISSCONNECTS ON HIGH AMP EQUIPMENT IS JUST ASKING FOR TROUBLE ) pump her down . Then use your recovery unit to lower the pressure further to 2/3psi then do a quick swap on the sensor . The holes in the sensor have no relavance as far as I have found and Ive changed more than I can remember . Just be sure not to bottom out the sensor in the pipe and DONT OVERTIGHTEN THE SWAGELOCK NUT YOU WILL CRUSH THE SENSOR INTERNALLY . Open all the valves and ur done .
    The toy chest is officially full ... I got a new toy..... 2007 Aston Martin V8 Vantage
    You bend em" I"ll mend em" !!!!!!!
    I"m not a service tech.. I"m a thermodynamic transfer analyst & strategic system sustainability specialist
    In the garage , greasin', oilin' . tweakin' n shinin' Roll on spring 2015 !!

  13. #39
    Join Date
    Jan 2005
    Location
    Houston TX
    Posts
    880

    Talking Out to lunch

    graham- Then I would have to say the instructors in Pueblo were out to lunch, because when I attended class for RTAA's way back when we were instructed to check a water or refrigerant sensor for accuracy the best way was having both sensors in the same fluid ( and they said water ice bath with an accurate thermometer) followed by an alcohol cleaning to remove residual moisture from the area around the sensor bead. I have no reason to disclaim what you said about the holes in the refrigerant sensor, but again both the school and the SB both specify that the sensors are position sensitive on the suction side and I have no reason to not follow the outlined procedure. This is just my opinion, then again both the school and SB-5 say to cut the sensor leads at the point of installation and wire nut the new sensor to the existing wire and I have never done that either. I always run the complete sensor and wire to the module and make a new termination on the new AMP plug. I don't leave the wire hanging either, I remove the now unused cable and run the new cable along the same frame rails. Let's face it graham we both know what we are doing. Be safe and keep building those cars. -Geo
    Once in a while everything falls into place and I am able to move forward, most of the time it just falls all over the place and I can't go anywhere-GEO

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