Issue:
How to troubleshoot a Traq flow sensor on IntelliPak rooftop units
Resolution:
How it works:
Whenever the supply fan is on and the fresh air damper is not closed, all of the outside air to the unit flows through 2 or 3 (depending on the unit size) air orifices. Within each orifice is an aluminum flow ring with connections to read the total pressure and static pressure. The flow rings are piped in parallel so that the transducer 3U219 is reading the average velocity pressure of all of the rings at once. This pressure information is used to calculate the actual airflow through the orifices.
The calibration relay 3L205 is energized every 60 seconds for about 4 seconds. During calibration the velocity pressure drops to 0" and the controller will take this value as "no flow". At the end of the 4 seconds, the transducer will again read the actual velocity pressure.
Step 1: Determine if the problem is air side or electrical.
Using tee fittings and short pieces of tubing, connect a low range (0-2"WC) or digital manometer to the 3U219 transducer with the tubes to the flow rings still connected. Connect the manometer in parallel to the transducer so that the manometer is reading the same velocity pressure the transducer is seeing from the flow rings. (high port to high port, low port to low port).
Depending on outdoor air flow through the Traq flow rings the pressure should be slightly positive, somewhere between 0.05" and 1.75". When the calibration solenoid is energized, the pressure should drop to 0".
Step 2A, problem is airside:
*If a negative pressure is seen, the tubes from the flow rings may be backward.
*If an extremely high pressure is seen (see chart below), the tubing may be loose or mispiped at the flow rings.
*If the pressure does not drop to 0" during the calibration mode (every 60 seconds), verify that the relay is actually being energized and that the tubing is clear.
*If the complaint is that the airflow is "always zero", the calibration sequence is suspect.
Step 2B, problem is electrical:
Read the DC voltage between the red and green wires at the transducer. 5VDC should be present. If not, trace the wires back to the VCM module, verify the VCM has 24VAC, etc. If 5VDC is present, proceed with the next test:
Unplug both tubes from the transducer and read the voltage at the black and green wires. The voltage should be 0.25VDC +- 0.05V. If not, the transducer has failed. If so, reconnect the tubes (with manometer still connected), start the unit, and proceed with the next test:
When the pressure is 0", the output voltage should be 0.25". As the pressure goes up, the voltage should go up as well. Use this table to see if the pressure and voltage match up.
| Pressure | Typical Voltage |
| 0" | 0.248VDC |
| 0.1" | 0.325VDC |
| 0.2" | 0.400VDC |
| 0.33" | 0.500VDC |
| 1.0" | 1VDC |
The chart shows that as the pressure goes up the voltage goes up, and during calibration the voltage drops to 0.25V. The exact values are not important; what is important is that every 60 seconds whatever value is seen during calibration is considered 0" pressure, and the unit will make all decisions based on this value. If the voltage does not change when the pressure changes, the transducer is bad. If the 0" pressure voltage is nowhere close to 0.25VDC, the transducer is bad.
Bottom line:
The problem is usually an air leak, mispiping, or plugged tube. Sometimes the calibration solenoid is bad, and rarely (last choice) the transducer has failed or the VCM is defective.
04/30/2020:
Check the VCM connection for the calibration solenoid and verify that it is connected to J6-2 and J6-3 on the VCM module. There has been several cases were the calibration solenoid wiring was wired at terminals j6-1 and J6-2 mistakenly.
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.