View Full Version : HP cutout on chiller - every 3 or 4 days? Operating readings posted

19-08-2014, 12:01 AM

I attended a call out today which was because one circuit on an R407C chiller cut out on HP. The landlords said it cuts out every 2 or 3 days on the same fault, and it's always the same compressor circuit (there are two circuits in the chiller). I recorded all the operating data for circuit 2 and there was nothing there that greatly concerned me; however the evaporating temperature seems low, but it's the same temp as circuit 1 which never cuts out - and the chiller provides the correct water temp. The evap superheat is bigger then I would like, but I can't see how that would directly lead to a high pressure cut out after a few days of running. I recorded the other circuit to compare and the results are near enough identical. I'm thinking there could be an issue with the HP switch, possibly cutting out at a lower pressure then intended. I wasn't able to test this during the visit as the HP switch isn't connected via a schraeder connection.

All three fan motors are working fine and are spinning the correct way, and the condenser coil is not dirty as we carried out a full maintenance on the chiller a few months back and the coil is fine.

My readings are:

Compressor 2 (The circuit that cuts out)

Condensing pressure - 16 BarG
Condensing temperature - 44degC
Discharge pipe temp - 87degC
Discharge Superheat - 43K
Liquid line temp - 38degC
Sub cooling - 49K

Evaporating pressure - 2.4 BarG
Evaporator outlet pipe temp - 1degC
Suction inlet at compressor - 2degC
Superheat at evap outlet - 15K
Superheat at compressor inlet - 16K
Evaporator temperature - -14degC

Water flow temp - 8 degC
Water return temp - 11 degC

AHU Supply air temp - 16 degC

Compressor 1 (The circuit that works fine)

Condensing pressure - 16 BarG
Condensing temperature - 44degC
Discharge pipe temp - 89degC
Discharge Superheat - 45K
Liquid line temp - 38degC
Sub cooling - 51K

Evaporating pressure - 2.55
Evaporator outlet pipe temp - 2degC
Suction inlet at compressor - 3degC
Superheat at evap outlet - 16K
Superheat at compressor inlet - 17K
Evaporator temperature - -14degC

What do you guys think of the above readings? Anything jump out?

Like I say the low evap temp and large superheat is slightly concerning, but with a return water temp of 11degC, the pressure would be low anyway in order to remove heat from the water.

cheers chaps

19-08-2014, 12:18 AM
Dammit. Just read through, my liquid line sub cooling is 6K....not 49/51K as I put..... Very tired!

19-08-2014, 12:23 AM

19-08-2014, 05:16 AM
first look at client load profiles and changes in production, lead lag on chiller as well. compressor load rates etc., client could be doing something different every 3 or 4 days and load responses are being effected that creates HP fault.
regards magoo

19-08-2014, 09:32 AM
Just check HP cut out, it's the first easy thing to check.
Raise the discharge pressure by whatever means if it hard example turn off condenser canes or restrict air/water flow.
Set it to 10-15% below relief valve setting or pressure vessel max rating design pressure.
Compare it to unit that runs ok.

19-08-2014, 07:53 PM
I would also be looking at the condenser fans, contactors, loose wire etc.

Without the condenser fans staging in as expected, a HP trip is likely.