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Agreed......

I can't tell you how many sensors I have changed on RTAA chillers, very common problem. I keep a complete set on every job with a RTAA chiller.

Well I guess you just get used to easily troubleshooting a sensor issue. When they go bad they are usually way off from each other so shutting it down and looking at the two sensors is about 99% for a good assesment.

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

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 .

Originally Posted by r404a

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.

Originally Posted by ga1279

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!

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

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

Originally Posted by BergerMech Rob

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?

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 could also pump the residual gas over to the condenser with a recovery unit.

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

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.

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.

Originally Posted by ga1279

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.

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Originally Posted by ga1279

Toptech- As you stated you are not that familiar with this chiller. So I would suggest you find a tech who is. They are not that complicated, but you can unknowingly do damage. That being said have you performed the EXV test ? The machine must be off at the UCP- Human interface before you can enable the test. 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. 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. Measuring suction line temperature is a false indicator as the actual sensing bead is a little red bead about half way in the suction end bell of the compressor motor. It has 6 holes that allow the moving refrigerant to pass around that bead probe and the compressor suction should only have the two single holes parallel to the flow and the 4 holes perpendicular to flow. If you never seen the refrigerant sensors you may not know what talking about.

I wouldn't recommend pumping this chiller down. If the LP switch doesn't work then you will run this compressor in a vacuum very quickly. Not good. I know of a tech that locked a 60 ton compressor up when he pumped it down and it went in a vacuum. I would pull it all out, do the cheecks you need and weigh it back in. This is only my recommendation, but what ga1279 said is correct.

RTAA going senseless

Toptech- As you stated you are not that familiar with this chiller. So I would suggest you find a tech who is. They are not that complicated, but you can unknowingly do damage. That being said have you performed the EXV test ? The machine must be off at the UCP- Human interface before you can enable the test. 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. 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. Measuring suction line temperature is a false indicator as the actual sensing bead is a little red bead about half way in the suction end bell of the compressor motor. It has 6 holes that allow the moving refrigerant to pass around that bead probe and the compressor suction should only have the two single holes parallel to the flow and the 4 holes perpendicular to flow. If you never seen the refrigerant sensors you may not know what talking about.

Also, you might already know but you can go into the panel and test the EXV for that circuit. You will have to count how many seconds between the clicking noise you hear. Should be close to 16 seconds in between. If I'm thinking correctly in the order it does, it will start out in the closed position and start clicking immediatley. Then will drive open and that's when you start counting. Then stop counting when it opens all the way up and starts clicking again when it hits its stop. When it again stops clicking, you will start counting again as it is on its way back to the closed position.

I don't understand why you have those sensor readings if you said they checked out ok and they are wired to the board in the right spot. I've always used resistance check on the sensors and not voltage. I also use my gauges and that usually does the job for pressure sensors.

I work on a military base and we have a bunch of knob dickers around here. so what I always do is make sure all the dip switch settings are correct, panel is configured correct as well as the settings. Sensors also have to be installed in the fitting properly, not too far in!

When the compressor starts it will start unloaded, the male unloader will be energized and the female and male load will be de-energized. When it loads, the female unloader will energize and shortly after the male unloader will de-energize. The male load will then pulse, and eventually the male unload will pulse at times. Compressor also stops unloaded.

I hope I didn't repeat too much you already knew!

The pressures you had didn't seem like it was loaded. Are those your gauges' press readings or the panels?

you don't have a suction line filter/drier in there do you?



infrared thermometers are not the problem (i use them all of the time)...the problem is 'emissitivity' and 'distance to spot ratio (or d/s)' and 'reflectivity'


look the terms up and know how to use your tools. once you do, an infrared thermometer is a very easy and accurate device to use.