1999 SAAB 9-5 Heat only blowing on setting

  • 1999 SAAB 9-5
  • 4 CYL
  • FWD
  • 97,063 MILES
Hello, recently I've encountered multiple heating/ac problems from a used 99 SAAB 9-5 I purchased. I have replaced my blower motor resistor, my blower motor, I just fixed the dreaded broked blend door on the drivers side and the heater core control valve. All in all, my whole system seems fine now and when I calibrate or run a diagnostic on my ACC system, I get no codes anymore. However, my heating system only seems to respond to a heat call when I set my heat setting to HI. The blend door on the drivers side will remain closed at all other settings, except when HI is selected (as I've used my rubber arms to reach up and hit the temp up to HI will running my A/C, and watching the blend door motor actuate with the components exposed under the dash liner. Any suggestions what may be causing? I am honestly almost at the end of rope with the vehicle, as 1 year with a SAAB has put me back about 5,000 in repair work.
Do you
have the same problem?
Wednesday, October 29th, 2008 AT 8:09 PM

1 Reply


I have attached a pic of all the components and the operation

From some of the information it stated that it senses if someone is in the seat. You sound like you do pretty good with flexibility, however, not sure if you can sit in the seat and do this.

My suggestion is to please review the information. Make sure all codes are clear and drive the car especially at normal operating temperature since you need the heat.

Then recheck for any codes and if it was operating okay.

I hope this helps.



Brief Description
The main purpose of the ACC system is to control the heating and ventilation units. It is to ensure that comfortable climatic conditions are achieved as soon as possible after starting the car and that these are subsequently maintained. The ACC unit comprises of a panel with display and buttons, and an in-built control module. Normally, the control module automatically regulates the following functions:

Temperature, separate for passengers and driver
The control module feeds current to a stepping motor that adjusts the position of the driver's zone air-blending flap. A further stepping motor adjusts the position of the air-blending flap of the front-seat passenger zone, and via a link the air-blending flap for the rear-seat passengers. The air-blending flaps mix cold air that has passed over the evaporator with warm air that has passed over both the evaporator and heat exchanger. The temperature at head height is calculated for the front-seat passenger and driver. The initial values are:

cabin temperature
outside temperature
time since the engine was last running
time since engine was started
mixed air temperatures
fan speed
sun intensity
The calculated temperatures are compared with those set by the driver and passenger on the ACC unit display. The set temperatures are adjusted slightly to compensate for the outside temperature so that the experienced temperature is equivalent to the temperature set. As soon as a difference arises, the mixed air temperature must be raised or lowered. The control module turns the relevant air-blending flap until the desired temperature is achieved. The link to the air-blending flap for the rear-seat passengers is set so that the temperature in the rear seat follows that of the front-seat passenger.
When the lowest mixed air temperature is set for both zones, the control module cuts off the flow of coolant to the heat exchanger using a vacuum operated valve so that the maximum cooling effect is achieved.
Certain engine variants are equipped with a circulation pump to improve the flow of coolant through the heat exchanger. The control module starts the pump when the engine speed and outside temperature are low.

Air distribution
The control module supplies current to a stepping motor that turns the air distribution flap of the driver's and front-seat passenger zone, and via a link the air distribution flap for the rear-seat passengers. In other words, air distribution is the same in the passenger and driver's zone.
The air is distributed to the defroster, floor/rear-door windows or panel outlets/rear centre outlets. Air distribution depends on the mixed air temperature set for the driver's zone. For high values (the driver's zone needs to be warmed) defrost/floor is selected. For low values (the driver's zone needs to be cooled) floor/panel or panel is selected. When starting in cold weather defrost is initially selected.

Fan speed
The control module regulates a control unit that supplies the fan motor with current. The fan current is lowest when the mixed air temperature is the same as the desired temperature for both zones (neither zone needs to be heated or cooled).
The current increases as soon as a zone needs to be cooled or heated. When starting in cold conditions, the outside temperature and temperature of the coolant determine the current. The fan current is limited when the engine is not running.

Air recirculation
The control module supplies current to a DC motor which turns the air recirculation flap.
Air recirculation is selected 45 seconds after starting the engine if the outside temperature is high and the desired mixed air temperature is low for both zones (both zones need to be cooled substantially).
Air recirculation is also selected in the following three cases:

when the outside temperature is very high
when the outside temperature is high and the oar speed low (performance of the A/C falls) when the outside temperature and coolant temperature are high (risk of engine overheating)
The control module requests the A/C compressor to cut in if the outside temperature exceeds 5 C and ECON is not selected.

Main Components


Heating and Ventilation


The climate system enables the cabin to be divided into two separate climate zones where one temperature can be set for the driver and another set for the passengers. This is done by means of three air-mixing flaps; one for the front passenger, one for the rear passengers and one for the driver.



Air Mixing

The air mix temperature is regulated by means of a stepping motor for each climate zone.

The driver's zone has one air-mixing flap, while the passenger zone has two, one for the front seat passenger and one for the rear seat passengers, which are connected by a link arm.

The air temperature from the heat exchanger is affected by the fan speed and the position of the air-mixing flap. On certain markets, the water passing through the heat exchanger can be turned off completely with a vacuum operated shut-off valve to obtain maximum cooling efficiency (cars with A/C).

Depending on the desired heating position/temperature, the air-mixing flap directs a certain amount of the incoming air through the heat exchanger.

If cold air has been selected, the air-mixing flap is closed so that air is prevented from reaching the heat exchanger.

Certain engine versions are equipped with a circulation pump for the heat exchanger. By increasing the flow of coolant through the heat exchanger when necessary, maximum heating efficiency can be obtained.

Bus Communication



In the Saab 9-5, all the car's control modules are connected to buses with the exception of the ABS and SRS control modules.
The bus is divided into the power train (P bus) and the instrument bus (I bus). Both busses are connected to the main instrument display panel (MIU). The busses are electronically separated.
The P-bus has a data transfer rate ten times higher than that of the I-bus.
All the information that one control module sends is available to all the other control modules connected to the bus. The MIU is responsible for ensuring that all the information on one bus is also available on the other.
The control modules send out information on the bus at regular intervals. The time between two transmissions depends on the information being transmitted and varies between 10 milliseconds (0.010 seconds) and one second . Information is also sent out by the control modules whenever the information changes.
The transfer of information between the control modules is achieved on two leads BUS+ (green lead) and BUS- (white lead). Both leads of the P-bus are twisted to increase the tolerance to electrical interference.

In a bus system, all the units must be able to communicate with each other. For example, the engine cannot be started if Trionic is unable to receive immobilizer information from TWICE.

Intermittent bus faults
Trionic and TCM check continuously to see that all the control modules they receive information from are communicating correctly.
In the event of an intermittent fault occurring in the bus communication, diagnostic trouble codes will be set in Trionic and TCM.
The cause of the fault can be that the power supply or one of the bus leads to the control module in question is absent.

Permanent bus faults
All communication between the diagnostics tool and the bus-connected systems goes via DICE. Irrespective of which system is being contacted, the diagnostics tool and DICE will check to see that all the bus-connected systems in the car are activated and communicating. If any of the bus-connected control modules are missing, the diagnostics tool will detect this. This means that all the bus-connected control modules are communicating correctly if there is no warning from the diagnostics tool.

Incorrect values on the bus
TRIONIC and TCM generate a diagnostic trouble code (DTC) when the information they fetch from the bus has an erroneous value.
The text in the diagnostic trouble code refers to the system in which the error exists.

ACC uses the following information:






ACC sends the following information:



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Thursday, October 30th, 2008 AT 12:12 PM

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