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Hvac Mode Stuck On Floor

george.underwood

By george.underwood
in Ask A GM Technician

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george.underwood Enthusiast

george.underwood

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1995 Silverado. HVAC mode is stuck on FLOOR. It was working ok up till a couple of weeks ago.

 

This is an older electronic control with 3 wires to actuator. I have part of a factory service manual and a Haynes wiring diagram. Control head is DELCO # 15-72267 (GM # 16233143)

 

I started it up with blower going, temp midrange, laid in floor with flashlight and actuated the MODE control from one side to the other. The actuator linkage did not move.

 

I probed the actuator signal input (white) with a voltmeter – with actuator connected. With engine and blower running, voltage ranges from 7.74V on VENT, 7.48V on FLOOR, down to 6.7V on DEF. Then took connector off actuator and measured – pretty much the same voltages (unloaded).

 

This does not seem to be enough range to me so seems like it would be the control, not actuator. I have a service manual but it gives no information on voltage ranges to isolate to control or actuator. What say the experts? Is there another procedure I can follow to isolate? (have not removed the actuator yet to see if it works in my hand).

george.underwood Enthusiast

george.underwood

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UPDATE

I removed the actuator, connected the connector and watched the rotation when moving the mode knob. It rotated but only a slight amount, probably not even enough to overcome the shaft lash. I was able to operate the door shaft by hand so it is not stuck. Im assuming at this point i have a bad control head. The slight amount of movement corresponds with the narrow voltage range measured on the control signal. Sure wish they would publish expected ranges for this stuff.

gmtech4 Senior Enthusiast

gmtech4

Posted
Posted

they do at the dealer,when you price out YOUR diagnoses and your wrong ,you will have spent the diag money ,so good luck brother,cross your fingers

george.underwood Enthusiast

george.underwood

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they do at the dealer,when you price out YOUR diagnoses and your wrong ,you will have spent the diag money ,so good luck brother,cross your fingers

 

I figure even if i end up replacing both the actuator and control head, its still cheaper than taking it to the dealership. (They would probably laugh at me if i took a 15 yr old truck there anyway). I usually dont pay dealer retail for parts either. Just ordered a control head on ebay (new in box OEM delco) for about a $45 savings vs local dealer retail.

 

If i had to pay labor for every repair to keep up these old trucks, i might as well buy new every few years like everybody else and have perpetual payments. I have another old truck i swap out to drive while waiting on parts and me to get around tuit. I keep it running, registered, and insured so thats another cost i should keep in the bottom line. Its also somewhat fun and challenging to me (im an engineer). Id rather do it myself and save money for retirement or some other toy. Maybe i'll eventually save enough to buy a new truck!

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