1997 chevy lumina-More A/C Problems

Hi, recently i have been having problems with my A/C blower motor. I checked all fuses and relays and everything was good. All speeds work but high (4th speed) cuts in and out but i never have problems with 1 through 3 after replacing the pigtail to the blower motor due to loose connections. Could the A/C fan speed switch have an intermittent problem with the high speed? I am thinking this is the problem being the circuit from the switch to the relay and from the relay to the blower motor/resistor is good. I have hooked up my multi-meter to the power input of the relay, When the fourth speed goes it drops down to no voltage to the relay.

Thanks, Any help is appreciated!

That sounds like a power problem to the High relay. Older models used a fusible link, later models had a Maxi fuse in the UEC. Then there are the connections....

That sounds like a power problem to the High relay. Older models used a fusible link, later models had a Maxi fuse in the UEC. Then there are the connections....

If i am correct, the relay supplies power to the blower motor resistor for speeds 1,2,3 and then from the resistor to the blower motor. But on the highest speed (speed 4) the power goes directly from the relay to the blower motor. But the relay is the same that supplies power to the blower motor or the resistor depending on the speed. Also, I have already replaced the relay and it still acts the same.

The three lower fan speeds are powered through the resistor and the relay N.C. contacts via the switch and Fuse 4. The high speed fan is powered through the relay N.O. contacts via Fuse 14.

what do you mean by N.C. and N.O.?

The relay is a single pole, double throw (SPDT). One pair of contacts is normally closed (NC) and the other contacts are normally open (NO). When the relay is de-energized, the NC contacts are closed and that's what powers the three lower speeds. When the relay is energized, the NO contacts close, carrying current to the blower at full (high) speed. That can only happen if the fuse and circuit powering the NO contact is intact. The fuse for HIGH is separate from the other blower speeds.

Okay, thanks for clearing that up. I think that fuse is in the passenger side dash fuse block, I checked and it was good.