HVAC system having a diagnostics controller associated therewith

1. A controller for a heating, ventilating and cooling (HVAC) system having an economizer with a damper and pressure sensors on opposing sides of said economizer, comprising;

a diagnostics controller having a program configured to:

use pressure difference sensor data and damper position data of said economizer to determine if a pressure difference across said economizer of said HVAC system is outside an operational design parameter of said HVAC system, wherein said operational design parameter is a function of a damper position of said economizer, and

generate an error signal indicating a return restriction problem when said pressure difference is outside said operational design parameter and said damper position is lower than a predetermined position, wherein said error signal specifies which one or more of the following conditions caused the return restriction problem: a duct restriction, an incorrect damper position, or a pressure sensor malfunction;

wherein said diagnostics controller is configured with a stored diagnostics data table relating said pressure differences sensor data with said damper position data, and wherein said diagnostics controller is configured to:

check pressure differences across said economizer at different damper positions during a continuous operation of said HVAC system, based on said stored diagnostics data table; and

use a persistence criterion routine to ensure that a fault persists before triggering said error signal during said continuous operation of said HVAC system.

2. The controller in claim 1 , wherein said diagnostics controller is configured to receive said damper position data from a HAVC system ventilation director.

3. The diagnostics controller recited in claim 1 , wherein said diagnostics controller is configured to check pressure differences across said economizer at different damper positions during a calibration period of said HVAC system, based on said stored diagnostics data table.

4. The diagnostics controller recited in claim 1 , wherein said stored diagnostics data table relates a damper position of 0%, 50%, and 100% to low limits of 0.05 h2o, 0.05 h2o, 0.0 h2o and high limits of 0.60 h2o, 0.25 h2o and 0.20 h2o, respectively.

5. A heating, ventilating and cooling (HVAC) system, comprising:

an economizer having a damper and an actuator to move blades thereof;

a pressure sensor configured to determine a pressure difference across said damper; and

a diagnostics controller having a program stored thereon configured to:

use pressure difference sensor data and damper position data of said economizer to determine if said pressure difference across said economizer is outside an operational design parameter of said HVAC system, wherein said operational design parameter is a function of a damper position of said economizer, and

generate an error signal indicating a return restriction problem when said pressure difference is outside said operational design parameter and said damper position is lower than a predetermined position, wherein said error signal specifies which one or more of the following conditions caused the return restriction problem: a duct restriction, an incorrect damper position, or a pressure sensor malfunction;

wherein said diagnostics controller is configured with a stored diagnostics data table relating said pressure difference sensor data with said damper position data, and wherein said diagnostics controller is configured to:

check pressure differences across said economizer at different damper positions during a continuous operation of said HAVC system ; and

use a persistence criterion routine to ensure that a fault persists before triggering said error signal during said continuous operation.

6. The HAC system recited in claim 5 , wherein said damper position data is based on a blade angle data of said economizer.

7. The HVAC system recited in claim 6 , wherein said HVAC system further comprises a ventilation director associated with said actuator and said diagnostics controller is configured to receive said damper position data from said ventilation director.

8. The HVAC system recited in claim 5 , wherein said diagnostics controller is configured to check pressure differences across said economizer at different damper positions during a calibration period of said HVAC system, based on said stored diagnostics data table.

9. The HVAC system recited in claim 5 , wherein said stored diagnostics data table relates a damper position of 0%, 50%, and 100% to low limits of 0.05 h2o, 0.05 h2o, 0.0 h2o and high limits of 0.60 h2o, 0.25 h2o and 0.20 h2o, respectively.