<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by GMPartsGuy:
If you put it on low/medium and it still blows high in those settings, it would be a high blower relay. If you have no fan at all in the lower speeds, then it would be the resistor. Easy to check with a VOM.
Dave </div></BLOCKQUOTE>
Unless you have a dead short somewhere, PartsGuy is correct.
If it runs in low through medium in high speed, pull the relay attached to the blower (under the I/P), if it now works in low through medium, the relay needs to be replaced.
If it still runs in high, you got problems.
If it only runs in high, and not in low through high medium (1-3, then sounds like the resistor, which is just left of the relay on the blower motor case.