My interior blower will work on 3 speeds for about thirty seconds and then drop down to the lowest speed. When it is working and I put in high(the fourth speed) it drops down to low immediately. I replaced the blower motor and fan which had frozen up with a new one from Toyota. I also replaced the heater relay. I'm wondering if the switch itself isn't bad. I looked at it but it would be a booger to get out. Any thoughts appreciated. It's hottern you know what around here. This is a 93 4x4 truck by the way. Thanks