98 GrandPrix GTP AC "issue"

Do you have the "automatic" HVAC system or the "manual" version?

I have the same issue with my 98 GT. Has anyone replied with resolution ?

-=Dann

A resolution depends a great deal on what type of system your vehicle has. The automatic HVAC controller uses electrical actuators to control temperature. The manual HVAC controller uses vacuum motors. More info needed from your end.

Surfer my '98 GrandPrix GT is an automatic. I found the external temp sensor for 15 bucks and I replaced it. I was sure that it was the solution. The temp gauge is good in the cold but will not report temps greater than 45 degrees. I had the AC unit checked and I was told that I'm AOK. Their advice was to replace the HVAC controller. And I did, but it was with one I picked up at the bone yard. No change... It was

-Dann

I have the auto controls. I plled apart the dash a little and can see the servos moving for the heat/ac on both the drivers and passengers zone. Cnat'tell or locate where the hot/cold mixer is (or if there is a seperate one).

Silver Surfer wrote:

My external temp sensor is dead-nuts on. I'm wondering if I don't just need a recharge? It is almost 8 years old and has never been in for any service (other than a cracked fuel pump resistor (TSB on that one) and regular oil changes. All I know s it was working fine two weeks ago..it sat in my driveway for two weeks during the super heat and then stopped blowing cold.

N> > A resolution depends a great deal on what type of system your vehicle has.

Take a look at this description and see if it shines any light on the subject:

Document ID# 515748

-------------------------------------------------------------------------------- HVAC Air Delivery/Temperature Control Circuit Description

The air doors that control the flow of air through the A/C module are operated by vacuum actuators. Solenoid valves located in the vacuum/electric solenoid apply vacuum to the actuators or vent the actuators. The solenoids are controlled by solid state circuits in the heater-A/C control. Push buttons in the heater-A/C control determine the A/C operating mode. Depending on the mode selected, the heater-A/C control determines which air doors should be operated.

Two air temperature sensors are used by the heater-A/C control. Their resistance decreases as the temperature increases. The inside air temperature sensor measures the inside air temperature. The ambient outside temperature sensor measures the outside air temperature. The difference between the two sensor measurements is used by the control circuits in order to determine whether the incoming air should be cooled or warmed, and to what degree. This is determined in order to bring the inside air temperature to the selected temperature as quickly as possible. If a malfunction should occur in either the inside air or ambient outside temperature sensor circuits, the heater-A/C control will set a trouble code. It will also substitute a temperature value of 75°F (24°C) if the inside air temperature sensor circuit is at fault or 49°F (9°C) if the ambient outside temperature sensor circuit is at fault. The substitute temperature value(s) allow the system to continue operations.

The sun load temperature sensor determines the amount of sunlight produced by the sun. As the sunlight increases, the sensors current increases. This sensor is used in order to program the blower speed and the auto/bi-level modes.

Air Inlet Valve The air inlet valve is closed in most of the operating modes, permitting outside air to enter the A/C module. It is opened only in the A/C modes and at a temperature setting of 65°F (18°C) or higher. When the air inlet valve is open, air from inside the vehicle is recirculated in order to get maximum cooling.

Air Temperature Valves The air temperature valves are positioned by the left and right electric actuators. When the door is in the cool position, air is prevented from passing through the heater core. The door can be placed by the actuator in any position between cool and warm in order to provide any degree of warming to the air after it has passed through the A/C evaporator core.

Defroster Valve The defroster valve can be moved to 1 of 3 positions. The defroster valve actuator consists of 2 chambers operated by 2 vacuum actuators. When the A/C system is operated in the bi-level of the DEFOG mode, neither vacuum chamber is evacuated and the door is in position B. Air flow is then directed to both the defrost outlets and heater outlets. If the heater solenoid is activated, the actuator moves the valve to position C. Position C directs air flow to the heater outlets (lower mode). If the defrost solenoid is activated, the valve moves to the defrost outlets. This is the position the valve is in when operating the defrost mode.

Inner and Outer Mode Valve The inner and outer mode valve is in position B when the air conditioning is activated, or when the bi-level or upper modes are selected. In this position, air flow is directed out of the A/C outlets. If the OFF, LOWER, DEFROST, or DEFOG mode is selected, the bi-level solenoid is de-energized. This will vent the vacuum from the inner and outer mode valve actuator, allowing the door to move to position A. The air flow will now be directed toward the heater and defrost outlets.

Outer Mode Valve The outer mode valve performs the following functions:

Diverting air-conditioned air through the A/C outlets Preventing air flow through the heater and defrost outlets. The outer mode valve is in position B when the system is in the maximum A/C or normal A/C modes. The outer mode valve is in position A in all other modes.

Delay Mode The delay mode is used in order to prevent the vehicle occupants breath from fogging the windshield when the outside temperature is low and the engine is cold. The heater-A/C control will set the doors so that air flow is directed to the windshield with low blower operation. The system will stay in the delay mode until the engine coolant temperature reaches 49°C (120°F) or after 4 minutes, whichever comes first. The system will then operate normally in the selected mode.

If you can get someone to put a scanner on your vehicle the following trouble codes might point you in the right direction any of them are set.

DTC Table TROUBLE CODE DESCRIPTION

01 or 101 DTC 01 Inside Air Temp Sensor Circuit Shorted

03 or 103 DTC 03 Outside Air Temp Sensor Circuit Shorted

05 or 105 DTC 05 LH air Door Motor Circuit Open or Shorted

07 or 107 DTC 07 UART Serial Data Line Fault

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Good news for the home team. When I got in my car today the temp readout for 103. :) good for me. I didn't have far to go today so I really couldn't test it but the system did seam to be blowing colder air. I think I might need more lbs's of R-whatever. I think the new ambiant air sensor fixed my problem. We'll see in the days to come. It jives with what the surfer published. Good luck to the rest.......

For future where did you find that info ? Please pass along the url is found on the web... PLEASE -Dann

The HVAC information came from the service manual for your vehicle which I have on CD. Bought a whole set of CDs on EBay a while back covering 1998 to

Could you post a link to an image of where the parts might be in the system. It's a little hard finding them all. I found a few of them.

-Thanks! Mike

Silver Surfer wrote:

I don't have a personal Web site or another place to post the pictures. Suggestions? Might have to email you something direct.

-Thanks! Mike

Silver Surfer wrote:

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Followup:

After reading the codes and analyzing wether the mixers were working I determined it might need a recharge. The moment I snaped the pressure guage on the compressor kicked off (low pressure saftey). A couple cans of coolant and it's good as new!

Thanks all for the help!