A/C - Imbalanced Temp From Right to Left/Up Down: Overview
Bulletin No.: T-92-30AFile in Group: 1
Number: 81
Corp. Ref. No.: 111101R
Date: Sept. 1992
SUBJECT:
HVAC DUCT TEMP AND/OR AIR FLOW CONCERNS/COOL AIR FROM DEFROST - IMBALANCED DUCT TEMPERATURE FROM RIGHT TO LEFT IN HEAT
MODELS AFFECTED:
1991-1992 DEVILLES AND FLEETWOODS
This bulletin supersedes Service bulletin T-92-30 which should be discarded. The revisions to this bulletin include new parts and additional diagnostic information for side-to-side and/or up-to-down temp variation. For imbalanced defroster operation on driver's side see bulletin T-92-14. For condensate dripping from the heater ducts see T-91-89. For whistling noise from HVAC temperature door a revised bulletin will be issued in the near future.
Some vehicle climate control systems may exhibit cool air from the defrost and side window defog outlets when operating in "AUTO" settings which call for heat or for defog mode. This condition may be described as causing cold hands, cold face, and/or cold left knee and is most likely to occur after a 40 to 45 minute drive as the interior vehicle temperatures begin to reach the desired setting and the system begins to stabilize.
As the ECC system begins to stabilize while in the heat mode, the temperature of the heated air delivered to the ducts begins to lower to help maintain the requested interior temperature. The system uses many hardware and software components to mix and deliver the air to the proper ducts to maintain comfort. The following components may contribute to the cause of this condition:
A. Inside Air Temp Sensor - may not be seated and/or sealed properly allowing heated air from the I/P interior to be drawn into the sensor producing a false sensor reading.
B. Aspirator Hose and Aspirator - hose may be kinked or damaged or aspirator may not be properly seated to module preventing the necessary air flow from the interior over the sensor.
C. Air Mix Valve/Door - may be misadjusted preventing the proper mix of heated and cooled air from entering the ducts. (Refer to Section 1B of the Service Information Manual for proper air mix valve adjustment.)
IMPORTANT:
It is necessary to inspect each of these items to assure a complete and satisfactory correction.
If after inspection of the above items no problem is found, then the problem may be caused by the improper mixing of the air by the baffles contained in the HVAC module. To correct this condition replace parts as shown.
Parts are currently available from GMSPO.
These PROM's contained enhanced control calibrations which are specifically designed to coordinate with the new baffles and splitter.
IMPORTANT:
If 1992 model and VIN sequence are after breakpoint N4257163 or if 1991-1992 models have had bulletin T-92-30 performed previously (on-board diagnostic parameter -31 would be 59 for 1991 and 67 for 1992), then there is no need to replace splitter wall or air mix door baffles. In this case only, just replace BCM PROM as indicated in step 26 of this bulletin. For warranty purposes use Labor Operation N4801 for .6 hour when replacing PROM only.
NOTICE:
To prevent short circuit damage when removing or installing certain electrical units, disconnect the negative (-) battery cable and turn ignition switch to "OFF" position.
CAUTION:
The procedure that follows must be followed in the order listed to temporarily disable the Supplemental Inflatable Restraint (SIR) system and prevent false diagnostic codes from setting. Failure to follow procedures could result in possible air bag deployment, personal injury, or otherwise unneeded SIR system repairs.
NOTICE:
The DERM can maintain sufficient voltage to cause a deployment for up to ten minutes after the ignition switch is turned off or battery is disconnected.
Disable SIR System:
1. Remove SIR fuse 18 from fuse panel.
2. Remove right and left sound insulators.
3. Remove Connector Position Assurance (CPA) and yellow two-way SIR harness connector at base of steering column.
Remove I/P Upper Trim Panel:
4. Remove A/C outlet deflectors and screws found behind each.
5. Remove three screws through defroster grill.
6. Disconnect connector from inside air temp sensor and aspirator tube.
7. Disconnect solar sensor from trim pad and remove upper trim panel.
Remove Lower Steering Column Opening Filler and Reinforcement Plate:
8. Snap out upper steering column filler and remove screws holding filler and reinforcement plate.
9. Lower steering column to rest on front seat.
Remove Lower I/P Trim Pad:
IMPORTANT:
Be sure to replace, not repair, filler trim and/or bracket if any damage to either part is evident.
10. Remove two screws and the lower trim pad support.
11. Remove the nut from accelerator pedal stud and the screw from I/P end of I/P lower brace and remove brace.
12. Remove remaining retaining screw and remove lower trim pad assembly from vehicle - two people required.
Remove A/C Distributor (refer to Figure 1).
13. Disconnect vacuum hose from vacuum actuators.
14. Remove vacuum harness retainers from air distributor ASSEMBLY and position vacuum harness aside.
15. Remove side window defogger hose/outlet ftom air distributor assembly.
16. Remove screws from floor air outlet.
17. Remove screws and nut attaching air distributor to front of dash and remove assembly.