YORK YVAC 307 SCREW COMPRESSOR FAILING LOW DISCHARGE SUPERHEAT R-134A

Hi guys new to the site here, but not new to the Hvac business, been doing it since 1977, I am a contractor in Southern California, well I got a york ycav that is really twisting my tail, got called out to site and I am told the # 2 compressor is failing on low discharge superheat, I look it over and see feed and drain valves are new and also the liquid level sensor in the flash tank, this chiller is air cooled and about 10 years old, the stepper modules are still original, so I reset it and watched for about 2 hours, r134 refrigerant, chiller set point 42 degrees, had 36 suc 130 discharge at 62 ambient, suction superheat 14.5 discharge super heat 5.4 and fighting to get up to 10 degrees, motor temps T1 68 T2 77 T3 78, 66% speed, economizer valve on,
Drain valve 75% feed valve 45 %, now the flash tank showed 0 % and bouncing to 5 and back to 0% , oil level on sperarator is just show a little in upper sight glass, but after 15 min of operation the motor temps were in the dumpster avg 66 degrees, failed low discharge super heat around 4 degrees, I did verify the drain and feed valves in service mode are opening and closing, customer assures me that he was there when the charge was weighed in 177lbs, the level sensor and valves were installed 3 weeks ago and customer said it will stay on line for more that 10 mins, if I remember correctly 10 mins is the max time for this Chiller wit low super heat on suction or discharge, the level sensor is the PEEK sensor and you are able to calibrate it,I thought that maybe the refrigerant is oil laden, and also going calibrate the level sensor, the amp draw looked ok, need to get the reading on that, also thought economizer is pulling liquid off of flash tank if the level is high flooding the lobes, can’t dischar above 105 degrees, well got invited Back on Wednesday to do some more digging on this chiller, well sorry to be the new guy here and drop a bomb, but any feed back would be helpful thanks for taking the time to read this book-lol

Probably a bad temp sensor.

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Originally Posted by chillrdude

Probably a bad temp sensor.

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yup. the problem with display panels is that nearly every tech walks up and believes them. verify all values before you use them. temp and pressure are usually pretty easy to verify. your suction temperature sensor is likely to have failed. your oil separator also has too much oil in it. these chillers need very little oil and too much can also cause issues like yours.

There is a blue letter about installing new valves on a older chiller, the connection at the valve is is where you disconnect for the cable. A new cable that goes back to the valve controller should be installed as well. If not done valve can act up, closed is open open is closed. If that were the case you can flood the evap. more then likely the valves may close thinking they were opening and shut you down on low suction. If you can see the valves respond correctly to commands thru the sight glasses good. Confirm if new cables were installed that they landed on the correct output, drain is drain feed is feed. Getting the cables pulled in is a pain.
Pull power to the economizer valve and see if that helps. The alarm shut down is 85% full on the flash tank. If the level sensor is off you could get liquid in the compressor thru the econo. line.
Verify all sensors, oddly enough if the level sensor is seeing 35% a lot of times the valve is 30-35% open as well. A suction line sensor that is off will get you a flooded evap. and low discharge temperature. Let know what you find.


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Originally Posted by jayguy

yup. the problem with display panels is that nearly every tech walks up and believes them. verify all values before you use them. temp and pressure are usually pretty easy to verify. your suction temperature sensor is likely to have failed. your oil separator also has too much oil in it. these chillers need very little oil and too much can also cause issues like yours.

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Hi Jayguy
well i did check the suction temperature and it was off by 12 degrees, had some sensors from a ycas, replaced it and all the numbers came back to the correct readings, 22 degree disc sh , 10 suction sh, motor temps 115 -125 degrees, i did check the cables from step controller to new valves and they are wired correctly, verified valve operation and they are opening and closing properly, will do a drive by on it tommorow to make sure it is all good, thank you for your input on this i really do appreciate it, patrick

just had the same problem the suction sensor reading high flooding the compressor driving down the discharge temperature its the same thing when the trane rtaa chillers does it.

The suction temp sensors on those are junk. I change them all of the time. The problem is they’ll read 5,10,15 degrees off, not 50 degrees off. Sometimes it’s not that far off so you don’t question it, you just trust the sensor. I have learned to never trust any of the sensors. 90% of low d.s. faults are caused by that. Once in a while you get a bad level sensor, and some carryover through the economize line.

I have to deal with the York chiller YCIV. The suction temperature sensor are reading off 15F. one of them shows >132.7F when the suction temperature is 55F. I know they are bad but still not unplug them. Can anyone tell me what type of suction temperature sensor that York uses for the chillers? many thanks

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Originally Posted by bangnhan87

I have to deal with the York chiller YCIV. The suction temperature sensor are reading off 15F. one of them shows >132.7F when the suction temperature is 55F. I know they are bad but still not unplug them. Can anyone tell me what type of suction temperature sensor that York uses for the chillers? many thanks

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part number should be on sensor.part numbers are000-00000-000 example.hose clamps strap to pipe under sound cover

high oil level

One of the issues with strapped on temp sensor is the straps are being over tightened. We have been using tape as substitute and have reduced failure rates. Once low SH has occurred oil carry over from flash tank will continue to keep discharge temps down and cause SH failure.

Hi. I changed the suction temperature sensor and that fix the problem. The compressor now is running at 100% during 3 days without any others problems. At the first run after changing, the superheat is still low. I though other problem appears, but it did not. The system needs at least 5 mins to stabilize.
So here is the tips. When you see the "low discharge superheat", record the suction temp, discharge time, and oil temp. Make sure they are similar. Next, let the system run until it is shut down. During the run time, measure the suction temp, discharge temp, and write down the motor temperature. If the motor temperatures are lower than 80F , that means the compressor is "flooded". Check the measurement temps with sensor temps, if they are so much different (>12F), that means the sensor is bad. I replace 2 bad suction temp sensor. One chiller has both discharge temp and suction temp sensor bad.

While I don’t agree with all of your tips, I am glad you got it fixed.