RTAA 1854 XRO1 A3D0 BFQ Sensors

[FREDIEFREON]

Hi All, My question is I have code 1d4, ordered replacment sensor sen0951, I seem to remember that they need to be changed in pair's ?? so is that the suction temp sensor on ckt 2 which is bad and which other one, also what direction dose the hole in the sensor face . thanks in advanced fred

[jayguy]

gotta change them in pairs...compressor and saturated evap temp sensors...no wire nuts...run the whole dang wire and loop it up under the unit nice and neat as the sensors are mated pairs WITH THE ENTIRE LENGTH OF WIRE INTACT.

most will say that you can just change one or just wire nut it in and it will probably work ok...but these same short cuts are done by the same guys who i am currently following around and cleaning up their mess. who knows...maybe that is why you are having problems.

[FREDIEFREON]

Thanks JayGuy, your right about messes, there are old sensor wires stiill hanging around from prevous change out and wire nuts galor

[cooolguy]

the holes face direction of flow

[FREDIEFREON]

Thanks Cooolguy,
Will be changing out tomorow
Fred

[milkyway]

gotta change them in pairs...compressor and saturated evap temp sensors...no wire nuts...run the whole dang wire and loop it up under the unit nice and neat as the sensors are mated pairs WITH THE ENTIRE LENGTH OF WIRE INTACT.

most will say that you can just change one or just wire nut it in and it will probably work ok...but these same short cuts are done by the same guys who i am currently following around and cleaning up their mess. who knows...maybe that is why you are having problems.

what happens when u dont change in pairs? and why and what does compressor and saturated evap temp sensors have in common that they r looking at? differntal to start or??

[Healey Nut]

The sensors are a matched pair (resistance wise) . Jay your correct no joints no wire nuts no butt connectors and use the right tool to make off the connection at the UCM . As far as dont cut to length ??? Do you see an extra 30ft of cable coiled up in the wire harness on a factory untouched unit ???? No they cut them to lenght to make it look tidy in the panel .
I always cut them and have not had any issues and it dont matter which way the sensor faces just make sure its not touching the bottom of the pipe that its in and dont overtighten the swagelock nut or you will crush the sensor internally and short it out.
As far as what they are looking at ......superheat

[jayguy]

...As far as dont cut to length ??? Do you see an extra 30ft of cable coiled up in the wire harness on a factory untouched unit ???? ...

you are absolutely correct. they don't leave any extra wire.

as far as what will happen? probably nothing. TECHNICALLY...there will an error in the readings. but, in practice, you will not be able to measure the difference anyway.

the reason for changing out both at the same time is to get as accurate a reading as possible since trane is measuring suction superheat by using 2 temperature sensors. with suction superheat as low as 4F, accuracy is important.

[Tech Rob]

Make sure you note the depth of the sensor. I usually measure it with a tape measure and make a mark on the new ones with a sharpie so I can get it right the first time and close it up quickly.

The easiest way to change them is on the fly right after a service pumpdown.

[ChillerWisperer]

the holes face direction of flow

Good one, mate!

[jayguy]

...The easiest way to change them is on the fly right after a service pumpdown.

isn't that a little 'illegal'?

[Tech Rob]

isn't that a little 'illegal'?

No, that's what I call "de minimus". I'm doing my part - allow me to explain. By not pumping the system down and transferring the remaining refrigerant to the condenser, I am not introducing non-condensables into the system, and subsequently contaminating the refrigerant, thus decreasing the amount of viable refrigerant that can be reclaimed when production stops.

[jayguy]

No, that's what I call "de minimus". I'm doing my part - allow me to explain. By not pumping the system down and transferring the remaining refrigerant to the condenser, I am not introducing non-condensables into the system, and subsequently contaminating the refrigerant, thus decreasing the amount of viable refrigerant that can be reclaimed when production stops.

that is how i do it.

[txhvac]

Make sure you note the depth of the sensor. I usually measure it with a tape measure and make a mark on the new ones with a sharpie so I can get it right the first time and close it up quickly.

The easiest way to change them is on the fly right after a service pumpdown.

Yeah you got get it right the first time, once that ferral fitting seats on the sensor...you're stuck with it.

[cperk]

Yes, I have seen guys jam it all the way to the bottom of the pipe, and when it's tightened, guess what happens to the sensor.