Problem with Heating/AC

My 99' Blazer LS is having issue with Heating the cabin as well as cooling it.

Here are my symptoms:

Air not hot, but mildly warm. But this afternoon when it was 45 degrees it brought hot air out.
Air will switch from Feet, to Defrost, to Front Panels.
AC will get cold briefly then stay slightly cool.

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Before you reply read what all I have done.

Radiator flush and replacement of coolant and hoses. Plenty of coolant in the system.
Recharged the AC system last fall. Checked out okay this summer too.

Thoughts or suggestions on this?

i think i heard something about a problem with the climate control switch on that year -- worth a check . what does the temp guage say - normal ?

Could be blend door or if an LT with auto climate (temps on dials) then an electric blend door motor also both seen behind glove box. Some info in the FAQs. Narrow it down - if when the heat is off you feel no heat but the AC is on/off then possible low pressure due to seal leak, compressor leak, or I've also had intermittent connector contact on the rear of the compressor so lighten pins and all OK. If heat on/off are you sure the heater core is freely flowing (assumes AC off) and may have to flush just the core - had that too so used 3' lengths of heater nose at the firewall and a garden hose and flushed both ways till freely flowing. Hope that helps.

Check under you hood on the driver's side fora ball looking thing and see if the vacuum hose has come loose if not follow it and check it for leaks and dry rot this is what works your vent doors.

Check under you hood on the driver's side fora ball looking thing and see if the vacuum hose has come loose if not follow it and check it for leaks and dry rot this is what works your vent doors.

If it is right near the Brake Fluid Reserve, then yes I have a rotted line just hanging there. I never could figure out where it went.

If it is right near the Brake Fluid Reserve, then yes I have a rotted line just hanging there. I never could figure out where it went.
That's your problem that is what runs your vent doors and heat door.

That's your problem that is what runs your vent doors and heat door.

Thank you for the response. I am going to try and fix it this week.