I am having troubles with the EXV (electronic expansion valve) on circuit A of a Carrier 30GT090 chiller.
The EXV continuously cycles, the measured superheat at the compressor suction sensor ranges between 5 deg F and 40 deg. F. The Service manual list total superheat at 30degF, (10deg after the chiller plus 15-20degF from the motor winding.)
I've tested and inspected the EXV and all works ok. The temperature sensors all check ok and the sight glass is clear so why is the valve continuosly overshooting?

The EXV on circuit B is working fine, maintaning right around 30degF superheat.

Any suggestions will be apprecieated.
Dan

Below are compressor stats when I was troubleshooting this morning. Outside air temp was in mid 50s.

Compressor A Running Conditions:
suct pressure: 40 psi approx
Disch Pessure: 140 psi approx
Chilled water entering temp: 29 degf
Chilled water leaving temp: 27degf
Saturated suction temp:13
Compressor return gas temp:varies 5 to 40F
Condensing temp:68F

Compressor B Running Conditions:
suct pressure: ? not recorded
Disch Pessure: 155 psi approx
Chilled water entering temp: 29 degf
Chilled water leaving temp: 27degf
Saturated suction temp:17degf
Compressor return gas temp:47degf
Condensing temp:69degf