Hello fellow Blazer's!

I recently sold my 96 Blazer LT (with manual A/C) and got me one of those 98 Blazer LT's with Computer Climate Control.
This summer I had no problems at all with the A/C, the selectors on Auto and everthing worked fine, the A/C light came on now and then when cold air was needed.
Now it is winter in Sweden and with that a lot of moisture. That means that that the A/C is really helpful when defrosting the windows, as it dries the air.

But I can't figure out how this CCC is supposed to work. I have tried the owners manual of course, but it is in Swedish, and I do not know where they found the guy who translated it from English...because it is impossible to make any sense out of it. So I'm turning to you, as I have had a lot of help reading the posts in this forum over the years.

When I select defrost on the ****, I would expect it to be possible to also press the A/C button, to getdry air fron the vents. But the only thing that happens is that the light in the buttob flashes for a second or two, then goes out. Is this normal? Is it not possible to get cooled air from the vents when defrost is selected?

Generally, the only time I get the A/C light shining (and the A/C working) is when the ***** are in the Auto position...
If i have selected fan or vents manually, the light only flashes when I press it.

If anybody with the CCC on a 98 Blazer could help me understand how it is supposed to work, then I might be able to talk to my favourite mechanic and get it fixed.

Thank's in advance.

/Björn

 

Welcome to the forum. The a/c compressor clutch is controlled by the PCM, and it will run the compressor any time one of the defrost positions is selected on the hvac control head, provided the ambient temperature is above 38 degrees F. If it is colder than that, the compressor clutch will not engauge.

here is a page from the service manual on your HVAC description and operation, I hope this helps.

Heating and A/C Operation
The purpose of the heating and A/C system is to provide heated and cooled air to the interior of the vehicle. The A/C system will also remove humidity from the interior and reduce windshield fogging. The vehicle operator can determine the passenger compartment temperature by adjusting the air temperature switch. Regardless of the temperature setting, the following can effect the rate that the HVAC system can achieve the desired temperature:[align=left]



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Recirculation actuator setting[/align][align=left]



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Difference between inside and desired temperature[/align][align=left]



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Difference between ambient and desired temperature [/align][align=left]



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Blower motor speed setting[/align][align=left]



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Mode setting[/align]The control module makes the following actions when automatic operation is not selected, and an air temperature setting is selected:[align=left]



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When the air temperature switch is placed in the warmest position, the control module commands the air temperature door to divert maximum air past the heater core.[/align][align=left]



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When the air temperature switch is placed in the coldest position, the control module commands the air temperature door to direct air to bypass the heater core.[/align][align=left]



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When the air temperature switch is placed between the warmest and coldest positions, the control module monitors the following sensor inputs to determine the air temperature door position that diverts the appropriate amount of air past the heater core in order to achieve the desired temperature:[/align][align=left]



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Sunload[/align][align=left]



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Duct temperatures[/align][align=left]



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Ambient temperature[/align][align=left]



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Inside temperature[/align]The following shows what blower motor and mode actuator adjustments are made for each air temperature switch selection when in automatic mode.





Component

Full Cold Position

All Other Temperature Positions

Full Hot Position


Mode Actuator

Panel

Automatic Operation

Floor


Blower Motor

High Speed

Automatic Operation

High Speed
The A/C system can be engaged by either pressing the A/C switch or during automatic operation. The A/C switch will illuminate when the A/C switch is pressed to the on position. The control module sends a class 2 A/C request message to the powertrain control module (PCM). The mode switch must be placed in the following positions for the A/C to be engaged by the PCM.[align=left]



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Auto[/align][align=left]



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Max A/C[/align][align=left]



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Bi-Level A/C[/align][align=left]



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Blend[/align][align=left]



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Defrost[/align]The following conditions must be met in order for the PCM to turn on the compressor clutch:[align=left]



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Engine coolant temperature (ECT) is less than 121°C (250°F)[/align][align=left]



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Engine RPM is more than 550 RPM[/align][align=left]



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A/C low pressure switch signal circuit is grounded[/align][align=left]



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A/C request signal circuit to the PCM has 8.5 volts or more[/align][align=left]



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Ambient air temperature must be above 3°C (38°F)[/align]Once engaged, the compressor clutch will be disengaged for the following conditions:[align=left]



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Throttle position is 100%[/align][align=left]



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A/C request signal circuit has 0 volts [/align][align=left]



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A/C low pressure switch signal circuit has voltage[/align][align=left]



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Engine coolant temperature (ECT) is more than 121°C (250°F)[/align][align=left]



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Engine speed is more than 5500 RPM[/align][align=left]



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Ambient air temperature is be below 3°C (38°F)[/align][align=left]



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Transmission shift[/align][align=left]



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PCM detects excessive torque load[/align][align=left]



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PCM detects insufficient idle quality[/align][align=left]



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PCM detects a hard launch condition[/align]When the compressor clutch disengages, the compressor clutch diode protects the electrical system from a voltage spike.
Automatic Operation
In automatic operation, the HVAC control module will maintain the comfort level inside of the vehicle by controlling the A/C compressor clutch, the blower motor, the air temperature actuator, the mode actuator and the recirculation actuator.
To place the HVAC system in Automatic mode, the following is required:[align=left]



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The blower motor switch must be in the Auto position[/align][align=left]



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The air temperature switch must be in any other position other than full hot or full cold position[/align][align=left]



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The mode switch must be in the Auto position[/align]Once the desired temperature is reached, the blower motor, mode, recirculation and temperature actuators will automatically be adjusted to maintain the temperature selected. The HVAC control module performs the following functions to maintain the desired air temperature:[align=left]



•
Monitor the following sensors:[/align][align=left]



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Inside air temperature sensor[/align][align=left]



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Duct air temperature sensors[/align][align=left]



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Ambient air temperature sensor[/align][align=left]



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Sunload sensor[/align][align=left]



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Regulate blower motor speed[/align][align=left]



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Position the air temperature actuator[/align][align=left]



•
Position the mode actuator[/align][align=left]



•
Position the recirculation actuator[/align][align=left]



•
Request A/C operation[/align]

 

Well covered, Bill, as always! I had a response typed up, then saw that you had posted a reply already.

 

Thank you very much for the extensive coverage of the subject!
I would guess the reason for the A/C not engaging (in my case) would be the ambient temperature.
I'll experiment with it a bit in light of all this information. Thank's!
/Björn

 

you're very welcome, let us know what you find.