climate control cluster

I have a 1991 ext cab 4x4 and am having trouble with the climate control cluster. Everytime I turn it on all of the lights flash. After about 4 minutes only the defrost works. If I go to change it to blow out of the vents or on the floor the same thing happens. I went to the wreckers and got a new one but the same thing is happening. Did I get a dud from the wreckers or is there another problem somewhere else. I have looked for a shorted wire but can't find one. Would this happen if a hose had a leak? Any ideas? Thanks