Came accross this for the Low A/C pressure switch. Not saying this is your problem. Just something to read and make you think or ask questions.Hopefully someone else has an answer.
INFORMATION
Bulletin No.: 04-01-38-010A
Date: January 21, 2010
Subject: Diagnostic Information to Accurately Diagnose A/C Low Pressure Switch Using Kent Moore Special Tool GE-47742
Models:
2002-2006
Cadillac Escalade, Escalade EXT
2003-2006
Cadillac Escalade ESV
1999-2007
Chevrolet Silverado
2000-2006
Chevrolet Suburban, Tahoe
2002-2007
Chevrolet Avalanche
1999-2007 GMC Sierra
2000-2006 GMC Yukon, Yukon XL
2001-2006 GMC Yukon Denali XL
2001-2007 GMC Sierra Denali, Yukon Denali XL
2003-2008 HUMMER H2
with Air Conditioning
Supercede:
This bulletin is being revised to update the model years. Please discard Corporate Bulletin Number 04-01-38-010 (Section 01 - HVAC).
Currently, technicians cannot accurately determine the air conditioning (A/C) low pressure switch open/close pressure point by measuring pressure at the low side service port. This is because the evaporator is between the low side service port and the A/C low pressure switch. Correlating pressures measured at the low side service port to actual pressures at the A/C low pressure switch port is difficult because of the multiple variables that impact pressure drop across the evaporator. Providing a pressure range that would take into account all these variables would result in a pressure range that would be too broad to be useful for diagnostic purposes. Kent Moore special tool GE-47742 will allow technicians to monitor the actual pressures at which the A/C low pressure switch opens and closes under actual operating conditions.
Technicians are to use the following steps to install and use Kent Moore special tool GE-47742 to measure A/C low pressure switch opening and closing pressures:
1.
Disconnect the wire harness from the A/C low pressure switch.
2.
Remove the A/C low pressure switch from the accumulator.
3.
Install the A/C low pressure switch, using the threaded port with an O-ring, onto special tool GE-47742.
4.
Install special tool GE-47742, with the A/C low pressure switch attached, onto the accumulator.
Important
Removing the seal from the A/C low pressure switch wire harness connector is required. Failure to remove the seal before plugging it into the switch will lead to misdiagnosis. The "plunger effect" of plugging the connector with a seal into the A/C low pressure switch induces a pressure on the back side of the switch. This pressure will skew the opening/closing characteristics of the switch 34-69 kPa (5-10 psi) until the pressure bleeds off. The time required for the connection induced pressure to bleed off can be 20 minutes or longer.
5.
Remove the seal from the A/C low pressure switch wire harness connector.
6.
Connect the wire harness, without the seal, to the A/C low pressure switch.
7.
Connect the low side service hose from the ACR2000(R) or GE-48800 to the service port on special tool GE-47742.
8.
Connect a Tech2(R) to the vehicle.
9.
Start the vehicle and maintain an engine speed of 1500 RPM. Set the HVAC controls as follows:
-
Set the A/C control switch to ON.
-
Set the mode control switch to A/C and engage recirculation mode.
-
Set the blower motor speed to LOW.
-
Set the temperature control to full cold.
-
Set the auxiliary blower motor speed to LOW. If equipped.
-
Set the auxiliary temperature control to full cold. If equipped.
-
The vehicle must be operating with no sun load (in the shade).
10.
Use the Tech2(R) to determine the A/C low pressure switch status and the ACR2000(R) or GE-48800 to determine the A/C low side pressure. Simultaneously monitor the switch status and the pressure at which the A/C low pressure switch opens and closes. The Tech2(R) will display switch status as "Normal" for Closed and "Low Pressure" for Open. A properly operating switch should open between 138-172 kPa (20-25 psi) and close between 275-317 kPa (40-46 psi).
11.
Remove special tool GE-47742 after diagnosis is complete.
12.
Install a new O-ring on the A/C low pressure switch port on the accumulator. Lightly coat the new O-ring seal with mineral base 525 viscosity refrigerant oil.
13.
Install the A/C low pressure switch onto the accumulator.
Tighten
Tighten the A/C low pressure switch to 6 Nm (44 lb in).
Important
Remember to install the seal back onto the A/C low pressure switch wire harness connector. Failure to replace the seal could result in terminal corrosion.
14.
Reconnect the wire harness to the A/C low pressure switch.
