[Hutch]

When my high speed fan relay was on the fritz(broken ground wire) the symptons were:
when the three speed switch on the a/c control was on low and medium it worked ok but switch to high it would go back to low.
I was troubleshooting the circuit when I accidentaly grounded the case of the relay. With the fan switch being in the high
position the blower increased substantualy in rpm's
Pay special attention to your ground leads. The high speed relay on near the kick panel has a black lead whick is attached to the firewall and the one on the dash lip is grounded through a screw to the case of the relay.