On my 99 blazer one day the heat and ac worked fine.Next day nothing works,Recirc,fresh,fan speed,rear defrost or automatic modes.Compressor is cycling as if ac is on .Anyone know thw problem.

Do you hear the blower motor come on at all?

No you hear nothing.I have checked all fuses and all are good.I work on my old classics but this is baffling.Nothing on that panel works including rear window defrost.

It could be a loose power connection going to the blower motor, or a bad blower motor relay, or the blower motor just took a dump.
Try running a jumper ground wire from the screws on the blower itself to a good ground under the hood, that was a coworker's problem on his 97'

No you hear nothing.I have checked all fuses and all are good.I work on my old classics but this is baffling.Nothing on that panel works including rear window defrost.

The only thing you can do at this point is check the harness that connects to the controls. Start following it back towards the fuse panel.
I had a similar issue with my power windows. It turned out that I had a couple of harness that were undone and the wires were rubbing on mounting brackets for the dash. This caused a bunch of shorts and burnt wires.

Once I got all that cleaned up all the electrical ghosts went away.

sounds like a control panel problem.

A bad power connection, or a vacuum leak.

Defrost will have the compressor cycling.

I don't believe it would be a vacumm problem.This Blazer has the optional automatic controls.Even the button for rear window defrost doesn't work and that has nothing to do with vacumm.Also the compressor is cycling with the selector switch in the off position.I am guessing electrical in some shape or form.

I don't believe it would be a vacumm problem.This Blazer has the optional automatic controls.Even the button for rear window defrost doesn't work and that has nothing to do with vacumm.Also the compressor is cycling with the selector switch in the off position.I am guessing electrical in some shape or form.

I'm thinking you might want to replace the whole assembly.

They can be purchased off of ebay cheaply.