Help! Trane sensor issues...

[zw17]

Trane RTAA240

Issue: code c195 or low saturated evap refrigerant temp

Hooked up the gauges and Cooper strap on temp sensor to suction line at compressor and found suction line sensor reading 16 degrees lower than my strap on. Fired up compressor and watched ODM reading plumet to -15 while Cooper strap on never went below 50.

Ohmed out both sensors and the 1st time I hit the suction line sensor it was jumping from about 52k to as low as 3.5k. Tested to ground, no shorts. About the 3rd time I hooked up the leads it leveled out to 10k which is right on the money with my temp readings. Checked wire for rubs or shorts, none found.

So my question is can this sensor short with oil in the line that is migrating? Have you ever seen a sensor that shorts in a given temp range? What else could factor into this thing giving wild ohm/temp readings?

I should also add that I changed the paired sensors a week ago, last one was reading 135 degrees static.

[Healey Nut]

I bet you overtightened the swagelock connector that seals the sensor in the line and crushed it internally shorting it out ???
Change them again and be very careful not to overtighten the fitting . Snug it up and soap test it . I only pump the system down to about 3psi vapour pressure and do a quick switch so no need to evacuate . Soap test at low pressure and then open up all the valves and retest at your static pressure . Also dont bottom out the sensor in the pipe .

[zw17]

I was pretty careful to not overtighten them or bottom them out. It was a Friday at 3pm so it was only pumped down to 40psi... I took a pretty nice oil bath.

I have new sensors on order for tomorrow.

[Healey Nut]

Also be careful that you put the 2 brass ferrules on the sensor the right way round and in the right order ??
Finger tight and 1/4 turn with a wrench to seal should be enough .

[ChillerWisperer]

Also be careful that you put the 2 brass ferrules on the sensor the right way round and in the right order ??
Finger tight and 1/4 turn with a wrench to seal should be enough .

Just make sure you hold on to the sensor between the "finger tight" and "1/4 turn with a wrench" steps. Especially when you have 40 psi on it. Don't ask me how I know this!

[milar]

Had the same problem but sensors did not fix the issue, exv checked out ok but I swapped the valve between the circuits anyway. Driver board checked out good. Still was tripping on low sat temp. Trane no longer sold that valve so I had to replace both exv's and driver board. Problem gone, old board looked ok chalked it up to F.M.

[mustardman]

You have the ucp1 panel and on a 240 there are a couple places you could have a bad connection, I have had issues with the press fit orange connectors on the board. Depending on whether you ran the cable the full length or just cut and spliced you may also want to check the condenser fan junction box because one of the sensors is wired and terminated there.