SUMMARY
This article describes how to fix a chiller with a microprocessor that is not receiving proper input signal from the pressure transducer.

SYMPTOMS
Microprocessor shows an “Err” on the top screen and a pressure transducer error code on the bottom screen. Pressure transducer errors include:

"tL1" for compressor 1 low-pressure sensor error.

"tL2" for compressor 2 low-pressure sensor error.

"tH1" for compressor 1 high-pressure sensor error.

"tH2" for compressor 2 high-pressure sensor error.

CAUSE
The Microprocessor is not receiving proper input signal from the Texas Instruments (TI) pressure transducer(s).

RESOLUTION
Several items, that are easy to check as follows, can cause transducer errors:

*** Before starting, make a note of THE transducer error code you are reading in the lower microprocessor screen *****

1. With power OFF to the chiller: Check wire connections from all transducers at the back of microprocessor board. Proper locations and color-codes for transducer wires can be found on the chiller wiring diagram located on the back of the electrical compartment door.

2. With power OFF to the chiller: Remove the molded plug from each transducer, blow out any dust or dirt and reconnect plug.

Note: In most cases, the steps above will correct the problem. After performing the above steps, turn the chiller and microprocessor on and check for the error. If the transducer error code returns, proceed to the following steps.

3. With power OFF to the chiller: Using the codes above, determine the physical location of the transducer that is producing the error and remove the “White” signal wire for that transducer from the back of the microprocessor.

4. Turn the power ON to the chiller and turn the Microprocessor ON. Using an AC volt meter make sure you have from 24 Volts AC and 28 Volts AC between the “24 VAC” and “COM” terminals at the back of the microprocessor control. If you do not have AC power in the range above, STOP as further troubleshooting of the chillers control system will need to be performed.

5. Using a DC voltmeter in the DC scale, measure volts between the “+5” and “COM” terminals at the back of the microprocessor. You should read 4.8 to 5.2 Volts DC. If you read NO volts or volts below 4.8, your microprocessor is defective and needs to be replaced.

6. Using a DC voltmeter in the DC scale, measure volts between the “+5” and “SIG” terminals at the back of the microprocessor. You should read 2.0 to 5.0 Volts DC. If you are not reading voltage between 2.0 to 5.0 Volts DC, then your pressure transducer or gray connection cable are not allowing proper signal to return to the microprocessor board.

7: Remove the connection cable plug from the transducer creating the error and swap the cable with another transducer cable on the system. If the error code moves with the cable swap, then the problem is in the cable. If the error code remains at the original location then the problem is in the transducer.

8. If the problem is in the cable, re-inspect the plug end. If everything seems to be in order, you will need to order a replacement cable.

9. If the problem is with the pressure transducer:

- Remove cable plug from the pressure transducer
- Using TWO wrenches, of the proper sizes, remove the transducer and inspect the inlet port. Make sure the internal (refrigerant side) of the device is clean and free of debris. Using WD-40 or ,other cleaning agent, clean the transducer. Once clean, re-install and test. If error code returns, the transducer must be replaced. WHEN ORDERING MAKE SURE TO REQUEST EITHER A HIGHSIDE OR LOWSIDE TRANSDUCER. THE TWO ARE DIFFERENT.

APPLIES TO
All chillers systems with PS microprocessor control.