Trane Chiller RTAA Diagnostic Problem

[svc]

Going bald rather quickly!
hope yall can help. I've got a trane air-cooled series r rotary liquid chiller with a latched fault of low superheat. This unit will run about 20 seconds after reseting. 90/225 with a 48 entering water temp and a 95 ambient. All sensors check out in correlation to temp/resistance charts and no high shorts to ground. The only thing that jumps out is a 400 psi suction pressure according to the trane display while my gauge shows 90psi. This 400psi reading on the display will sometimes show normal. What is causing this false reading on my display. my book also shows normal superheat is 4 degrees and will alarm @ 2400 degree f seconds if falling under 2 degrees. can anyone please help and possibly feel me in on tranes mathmatics of degree seconds.

Or does anyone have a spare chiller!

[qtip]

The psi is calculated by the temp input from the sensors, sounds like you have a bad suction temp sensor. Replace in pairs as per Trane instructions.
Another thought is the sensor is inserted wrong and due to expansion/contraction you are getting a short causing the wrong temp reading which creates the high pressure reading on the display.

[airworx]

sensor can read normal then go crazy and back to normal.
i would replace the sensor.

[rob10]

As stated, change as a pair.

[flemsteele]

Part # SENS0951!!!

[cold-n-mode]

as stated above sen-0951 matched set will fix the problem the chiller only knows what the sensors are telling it.

[svc]

Thanks for the replies got a new sensor put in. works great Im not to impressed with tranes troubleshooting guide because the temp/resistance chart showed the sensor to be perfect on the bad sensor and their was no short to ground.

[trimble]

Sometimes the problem is a loose connection where the wires are pierced at the plug on the 1U3 module.

[acjourneyman]

If the wire gets folded over from the stainless and the wires get bared it causes nuisance problems like this.If someone steps on the sensors they are pretty well toast.

[chiller-thriller]

Other day RTAA wouldn't start, every thing seemed normal except that the leaving chilled water temp was 40F, entering 78F, no compressors on, some hair brained scheme of swapping sensors to see if she'll go. After swapping them both physically and electrically, they both read 78F, what the hey, I started they chiller, no problem. Went and checked some other units, came back still running. Put the sensors back to normal, ten days no trouble with sensors. Now to fix the leak on the braze joints on the condensers. This unit was a 2000, I am interested in all your experiences with these machines, good and bad. Cheers.

[scott123]

The problem usually is a overtightened compression fitting on the sensor. This (over time) causes the sensor to fail as you describe.

[dmedley]

if you look closely at the sensor placements of each circiut
you will find that each ckt has 2 sensors. one on the
suction side of the compressor and one after the exv valve.
what is happening is that the sensor after the exv is worn
due to the liquid wearing down the sensor.this sensor shows
us on the display saturation temp. and the sensor at the
suction side of the compressor shows us suction temp.the
difference between the two is superheat. if the sensor near
the exv is reading lower than the other it will shut the
chiller down on low super heat.cycle the power off to the
unit, reset diagnostics and pump each ckt down to change the
sensors. be sure to shut the liquid line valve off to each
ckt then open it after you change out the sensors. this will
correct the problem.dont forget to check out the fan motors
for shorts and resistance between the windings. this will
give you more headaches as well if you dont do this.

[btexpress]

Chiller-Thriller,
You asked about other problems that we have incurred with these units. I have found on several older (blue light specials) that the wire ties Trane used to support the wiring for the condenser fans would rub through the wire's insulation and cause grounds to the fan support brackets. If you start finding cond fan motors blowing fuses or showing grounded, check those wire ties.