97 Explorer brake go to floor

I have a 97 ford explorer and recently had the brakes done. The brake pedal occasionally would go to the floor and then build pressure right back. I had the brakes bleed and thought it was better until it did it again. It doesnt happen but ocasionally and I was told that it can be a bad ABS valve??? or the master cyclinder. I was wondering if there is an ABS valve, where is it? and should I replace it before the master cyclinder: and if it is the master cyclinder is it as simple to replace as it looks?

I was searching the forum and notice some replies say to remove the abs fuse. Will that allow me to see if the ABS system is failing? Will I still be able to drive the truck safely, wife's truck.