A/C & heat only blow sometimes?

I have a 1995 ford explorer and I had my a/c recharged thinking that was the problem. The air blew out for out from a/c and heat for about 3 days and then it was done. Now in the mornings I turn my heat settings on and nothing happens except for this little hissing sound and no air. But sometimes air does blow out usually after its been running a while. But I've had mornings where it decides to work right away

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