1995 Chevy S-10 Blower Motor

Thank you very much for your helpful information JDL.I will look for the relay tomorrow using the wire colors you listed. I will keep you posted on what I find. I have a cheap Haynes manual and they did not give me the blower motor, switch, and relay wiring in the electrical diagrams so the information you posted is critical for helping me continue on this problem. After I check that, I will try to get right on the plug going to the blower motor and see if the voltage increases to 12 volts when the switch is thrown into high position. If it does, I guess the motor has to be bad. If it does not, I guess the relay has to be bad. I don't think any of the resistors are used when you switch into high speed. The blower is supposed to get the full 12 volts and run at top speed.

The problem with the fan not running on high speed seems to be getting more frequent. I checked voltages at the switch itself when the blower did not come on in high speed and the switch seems to be working. The resistors are the old type of spring wires, which are more reliable than the newer electronic ones. The thing that makes me think that a relay is sticking is that on one single occasion when I shut the engine off and removed the keys the blower motor kept running. I had to start the engine about four or five times and fool with the controls and it finally shut off. I thought I was going to have to disconnect the battery for awhile.

Your diagram was helpful JDL.I can understand how the circuit works from the diagram you sent. Here is what I found and did up until now.I had no voltage at the blower motor when I threw the switch into high so I went to a junk yard and pulled the three relays. They have to be changed as a unit on the 94 and 95 Chevy S-10. When I got back home and unplugged the relays I found that the one in your diagram going to the blower motor had the plastic melted around the red wire inside the relay as well as in the plug. I will have to go back to the junk yard to get the plug end of the relay. The resistor block has coiled wires with three Zener diodes across the three coils of wire. They illustrate the three Zener diodes in the "resistor block" as three resistors in your diagram. It should be illustrated as a three Zener diodes. This figures because that is how they drop the voltage for the three lower speeds other than high. Zener diodes will have a voltage drop across them. Zener diodes are used to regulate voltages in power supplies. You can see in your diagram that if the signal comes in at the resistor block at pin B on the left then you would be operating at the lowest speed. Some voltage would be dropped across all three Zener diodes to give you the lowest speed out of the blower motor. This would be determined by the position of the switch. If it comes in on the pin next to it, you would be operating in the second lowest speed. If the signal comes in on the third pin then it is operating on the second highest speed. If the blower is in high, 12 volts is sent from the switch through the red wire and the relay directly to the blower motor. Knowing what I know now about the 94 and 95 Chevy S-10, I would advise everyone to look at the connections on the male and female plug connections going to the relay. I suspect that these will be burned in many, if not most, instances where the blower motor stops working in high speed and/or the motor continues to run when the engine is shut off.

Thanks again JDL. Here is the final solution. There is a red wire going into the relay that bypasses the resistor block. This wire is always hot. When the switch is thrown into the highest speed the relay kicks in and 12 volts is connected to the blower motor through the red wire going into the relay and the purple wire coming out. The red wire got hot at the connection inside the relay burning up the relay and the plug. That connection takes a lot of current running the blower motor at high speed. I changed the relay and was getting 12 volts into it but coming out of the plug I had nothing. The plug was toasted also. Those two things - the relay and the connector attaching to it were both bad.

I went to a junk yard and they gave me the assembly with three relays the GM says you have to change together. I paid $15. All three relays are the same. The reason GM says you have to change them together is because it is physically very difficult to remove one and put the another one in. When the blower motor won't shut off in an S-10 even when you turn the engine off the contacts in that relay are stuck in the energized position. It is possible to change one relay, so now I have two spares. I made a second trip to the junk yard and they gave me the plug for free. The resistor block has nothing to do with either symptom I experienced. A word of advice to anyone who has a Chevy S-10 blower motor that runs in high speed all the time, even when the engine is shut down and all switches are in off or low position - this is caused by the relay. Usually, you will lose the highest of four speeds in the blower motor first. In some cases you will see this second symptom if the contacts in the relay get welded together and the relay won't kick out. Take the connector off the relay and give it and the relay a good visual inspection.

I plan to change my relay every 100,000 miles with one of my two spares. :)

Dear gentlemen, those are definitely NOT zener diodes in the blower motor resistor assembly. They are thermal fuses. Available from China for about $1 each. With a voltmeter across them they will show about.2 ohms resistance. Completely different function and characteristics from diodes.