1990 Chevy Suburban A/C relay only works when I tap it

Yes bought two seperate new ones. All 3 do it.

Does that relay have a ground wire or are you talking about the fan motor being grounded.

They are spade terminals 6 of them

It looked a little nasty, so I took apart the male part of the socket and pulled out the individual wires, the red power wire looks like it may have shorted out at some point because it has burn marks on it and the plastic. Even so, it's still in pretty good shape and has a good connection to the relay. I just now finished up re grounding it hoping that was the cause. I even ran a wire from the original ground location to a better location on the chassis. I guess my next step is to look at that red wire. The volt meter says 13 volts though, yet it still only clicks on with a tap of the screw driver.

Thanks for your help, it's been very informative.

Could it be the switch inside the vehicle? I turned the truck on, tapped the relay to get it started, then moved the switch from high, to the next one down and it worked, then moved it back to high and it worked, then moved it all the way to the lowest setting, and it wouldn't come back on

Blower motor, sorry for the technical mis understanding. I fixed the issue. It was the control switch inside the dash.

I have to say I know a lot more about how my a/c works now.

Thanks,

Nick