Issue:
Supply Air Pressure Sensor Failure
Resolution:
IMPORTANT NOTE: Voltage and pressure readings in (PARENTHEIS) indicate values for all Ipak 2 units and Ipak 1 units built after 02/2009
SUPPLY AIR PRESSURE SENSOR FAILURE
The supply air static pressure sensor is used on Variable Air Volume (VAV) units with Inlet Guide Vanes (IGV) or Variable Frequency Drives (VFD). This diagnostic occurs when the voltage output from the transducer is outside the range for normal duct pressures. Normal pressures range from 0.00 IWC to 5.00 IWC (0.00 IWC to 7.9 IWC). During normal operation if the voltage dips below 0.04 VDC or rises above 4.75 VDC the diagnostic will be generated.
Items to check include:
1. wiring
2. sensor
3. control module
4. pneumatic tubing connections
Here are the steps for the Intellipak (legacy) Rooftop
Step #1 Wiring Errors
The supply air pressure transducer connects to the Rooftop Module (RTM 1U48) at pins J5-6 (+5 VDC), J5-7 (signal from transducer), J5-8 (common). Verify that the wiring is correct, all the plugs are connected, and the voltages are present at the transducer. Refer to the unit schematics for wire numbers. (As a note, on units with Variable Frequency Drives (VFD), it is very important for the sensor raceway wiring to route high through the unit and the power wiring to route low. If this is not the case, the VFD can interfere with the operation of the sensor, and the wire routing will need to be corrected.) If the wiring checks good, continue to the next step.
Step #2 Pneumatic Tubing
Ipak 20-130 Pneumatic Tubing
Refer to above diagram for proper tubing connections for the transducer. Verify that factory installed tubing is correct and there are no air leaks. Also verify that outside air static pressure reference is properly installed. If the outside air static pressure reference is not properly installed, rainwater can enter the tubing. If this is the case, correct the installation and dry out the pneumatic tubing. The customer installed tubing should be connected as shown in the above diagram. If all appears to be correct, continue to the next step.
Step #3 Sensor Checkout
0 to 5 IWC Transducer
Ipak Sensor Checkout
The formula for the above chart is V = iwc * .75 + .25 ; where v = voltage and iwc= inches water column.
-.75 to 9 IWC Transducer
Tee a manometer/magnehelic into both the high and low ports on the transducer. Verify that the voltage read at J5-7 and J5-8 on the 1U48 module corresponds to the pressure indicated on the manometer using the chart above. As an easy reference, notice that 0.00 IWC equals 0.25 VDC (0.53 VDC). If it does not and Steps 1 and 2 have been performed, replace the transducer. If the voltage corresponds to the pressure, proceed to the next step.
Step #4 Control Module
If all the previous steps have been performed, the diagnostic remains, and no errors are found, replace the 1U48 module.
WARNING:
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.