Auto Air Conditioning & Heater Repair: high speed does not work on heater fan motor, chevy dealer, astro van

Question
I have a 1995 Astro Van and the high speed on the blower switch does not turn the blower on at all the other 3 speeds work. I need to know why it does not turn on the blower. I changed the relay that is mounted on the firewall that is suppose to operate the high speed to the blower. Does the aircompressor have to work before the high speed fan will work? Or is their a relay just for the air conditoning system. The air conditioner does not work because it compressor locked up according to the GM Chevy dealer. The wire that is connected to the clutch is disconneted. I put the control switch to a/c position and then checked to see if any current is comming out of the connector that connects to the clutch and thier is no votage. I hope I gave you enough imformation to describe my problem. Thank you very much,mabe you can help me to fix this problem.


Answer
Richard,
This is odd, usually high is the only speed that you will have when the fan starts acting up. But if you have a test light or multimeter, here are the checks that need to be made. No your compressor does not need to be on to operate the fan in high.

With your ignition on and blower switch on high...
Check voltage between orange wire on blower switch. If you have voltage, go to the next step, if no voltage, replace your blower switch.
Check voltage at the orange wire on the high speed blower motor relay connector. If you have voltage go to next step. No voltage - repair the break in wire between switch and relay.
Check voltage on the black wire of the relay connector. If you have voltage, good guess... next step. No voltage, repair the break in the line between the black wire and ground.
Finally, Check for voltage at the red wire of the relay connector. If you have voltage, replace the relay, maybe you got a bad one from the parts store. If no voltage, repair the fusible link or broken wire between the relay connector and the fuse box.
If you have voltage at all of these points, the only thing left is the wire leading to the motor from the relay being broken.

Thank you for the question, I hope I was of some assistance. If I can do anything further during this process, or in the future, please do not hesitate to ask. If you found this response to be of some assistance, please remember to rate this answer. Thanks again and good luck in everything.