Those wire counts and colors don't agree with the Blazer or S10 wiring diagrams. Is this a Trailblazer or Bravado or something other than a vanilla Blazer or S10?

George

 

and which engine?


George

 

Standard 2000 Chevy Blazer LT 4.3 rwd

 

Hooking up the test light I have power coming in to the resistor but no power coming in to the blower motor. It’s a brand new resistor so I don’t think it would be bad??

 

Dk blue is the output wire on the resistor network, do you have power there in fan positions 1, 2, and 3 (the bulb should change intensity)? If so, does that power make it to pin 87A in the relay socket?

When the fan speed is on 4 (high) there is a different power path to the blower motor. Put the fan speed on high (4) and see if there is power on pin 86 of the relay socket.

Is there always on power to pin 87 of the relay socket?


George

 

Also, I got to where my shop manuals are so I can see the detail of the HVAC control unit connectors and wiring. When you get a chance post another picture looking more into the back of the unit at a slight angle so we can see all of the connectors and wiring.


George

 

This is the back of the control unit. The relay is noticing the switch of the fan speed and is sending power to the corresponding pins to the resistor. Once it gets to the resistor I am not getting any power out of it to the blower motor pin.

 

OK, I took a detailed look at the wiring and connectors on the back of your HVAC control unit and now we can use your test light to check power in and out of the unit. There is a cluster of vacuum hoses which can ignore and there are 5 electrical connectors, You can identify the connectors because each one has a different set of colored wires:

C1: 10 pins. wires are Gray, black
C2: 3 pins. wires are light blue, brown, brown
C3: 3 pins. wires are brown, light blue and black
C4: 5 pins. wires are orange, light blue, tan, brown
C5: 4 pins: wires are gray, brown, white, black

The power into the control head for the fan speeds is on the outside brown wire on C2. Pull the connector or back probe that wire (even better) and check for power

In any selector position except off the output from the selector switch to feed the fan speed selector is on middle brown wire of C2 which has to be checked with the connector in place.

That power output is spliced into the C4 connector and enters the fan speed selector switch on brown wire of C4. With C4 connected you should see the following at the resistor connector (disconnected):

Power always on the brown wire
Power on the tan wire in fan speed 2
Power on the light blue wire on fan speed 3

Back up on the HVAC control module you should see power on the orange wire of C4 with the connector attached with fan speed 4 (high).

With all connectors in place you should see varying levels of power on the dark blue output wire of the resistor network.

If you have not found any problems at this point then we can move on to the relay, wiring and ground for the motor.


George

 

Clockwise starting adjacent to the vacuum hose connector its:

C2
C3
C4
C1
C5

For fan speeds 1-3 the power goes from the hvac control head to the resistor network and then out on dark blue to the relay pin 87a. For fan speed 4 (high), the power for the motor bypasses the resistor network, leaves the hvac control head on orange wire to the relay pin 86 which then energizes the relay to take always hot power from the fuse panel and routes it through the relay to the motor. At rest the relay just passes the resistor output power through to the motor. In high fan speed the relay is energized which disconnects the resistor power output and switches always on power from a different fuse to the motor with no power limiting resistors involved.


George