99-02 A/C Auto Recirculation Option
03-27-2012, 12:27 PM
#1
99-02 A/C Auto Recirculation Option
What functionality do you lose when you remove this wire from the red connector pin 33 and use that pin for high speed electric fan control on 99-02 trucks? I just programmed an 00 Silverado for electric fans using this pin for fan control and all the HVAC seems to be working just like before. We thought we might lose the A/C recurculation but when you engage that switch on the HVAC control, it seems to function correctly.
03-28-2012, 06:07 AM
#5
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There is a high pressure switch that at 325 psi tells the PCM to turn the AC over to recirculate in an attempt to keep the high side pressure down. Recirculating cooler air back across the evaporator puts less heat into the system in turn bringing the high side pressure down. With electric fans there really isn't a need for it but anytime its above 90 I keep mine on recirculate just because. FWIW this function was very obvious on my dads 2002 duramax this past summer towing in 115 degree heat. Everytime we slowed down or came to a stop the recirculate would come on and once we got going it would turn back off.
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03-28-2012, 07:46 PM
#8
There is a high pressure switch that at 325 psi tells the PCM to turn the AC over to recirculate in an attempt to keep the high side pressure down. Recirculating cooler air back across the evaporator puts less heat into the system in turn bringing the high side pressure down. With electric fans there really isn't a need for it but anytime its above 90 I keep mine on recirculate just because. FWIW this function was very obvious on my dads 2002 duramax this past summer towing in 115 degree heat. Everytime we slowed down or came to a stop the recirculate would come on and once we got going it would turn back off.
03-29-2012, 05:17 AM
#9
I found some interesting information
1999
The recirculating door motor is controlled by a signal from the HVAC control module via CKT 1614 (DK GRN) when the push button is activated on the control head. Also, the door motor can be controlled by the PCM/VCM which monitors the automatic recirculation switch activity. The automatic recirculation switch is located at the bottom right hand side of the A/C condenser. The switch will signal the door motor to the recirculating mode when the switch closes due to high refrigerant pressure. This will allow cooler air from inside the vehicle to flow over the A/C evaporator thus cooling the refrigerant temperature.
Automatic recirculation mode will become active when the A/C high side pressure reaches 350 PSI (+/- 30 PSI) and remain ON until the high side pressure drops below 240 PSI. In automatic recirculation mode their will be no indication on the HVAC controller that the mode is active, the out side air (OSA) and recirculation (REC) switches and indicators will be inoperative on the HVAC controller.
2001
Manual System
Automatic recirculation mode will become active when the A/C high side pressure reaches 2206–2620 kPa (320–380 psi) and remain ON until the high side pressure drops below 1447–1861 kPa (210–270 psi). In automatic recirculation mode their will be no indication on the HVAC controller that the mode is active, the out side air (OSA) and recirculation (REC) switches and indicators will be inoperative on the HVAC controller.
Auto System
Recirculation Mode
The recirculation door will move automatically with an input from the A/C high pressure recirculation switch. The PCM will place the A/C system in recirculation mode when a signal is sent over the A/C refrigerant high pressure cut-out switch signal circuit. This allows for the cooler inside air to flow over the A/C evaporator and cool the refrigerant temperature, until the high side pressure returns to normal. The PCM sends a Class 2 message to command full recirculation at 2896 kPa (420 psi).
The recirculating door motor is controlled by a signal from the HVAC control module via CKT 1614 (DK GRN) when the push button is activated on the control head. Also, the door motor can be controlled by the PCM/VCM which monitors the automatic recirculation switch activity. The automatic recirculation switch is located at the bottom right hand side of the A/C condenser. The switch will signal the door motor to the recirculating mode when the switch closes due to high refrigerant pressure. This will allow cooler air from inside the vehicle to flow over the A/C evaporator thus cooling the refrigerant temperature.
Automatic recirculation mode will become active when the A/C high side pressure reaches 350 PSI (+/- 30 PSI) and remain ON until the high side pressure drops below 240 PSI. In automatic recirculation mode their will be no indication on the HVAC controller that the mode is active, the out side air (OSA) and recirculation (REC) switches and indicators will be inoperative on the HVAC controller.
2001
Manual System
Automatic recirculation mode will become active when the A/C high side pressure reaches 2206–2620 kPa (320–380 psi) and remain ON until the high side pressure drops below 1447–1861 kPa (210–270 psi). In automatic recirculation mode their will be no indication on the HVAC controller that the mode is active, the out side air (OSA) and recirculation (REC) switches and indicators will be inoperative on the HVAC controller.
Auto System
Recirculation Mode
The recirculation door will move automatically with an input from the A/C high pressure recirculation switch. The PCM will place the A/C system in recirculation mode when a signal is sent over the A/C refrigerant high pressure cut-out switch signal circuit. This allows for the cooler inside air to flow over the A/C evaporator and cool the refrigerant temperature, until the high side pressure returns to normal. The PCM sends a Class 2 message to command full recirculation at 2896 kPa (420 psi).