Rep Power: 0

A/C intermittently works, usually at startup. Then cuts out and blows warm/hot air (depending on outside temp and engine temp). When it's blowing warm, the compressor is not engaged. Replaced the fuses and compressor relay switch. Compressor still cuts out and the system blows warm air.

I did have the system recharged at Valvoline two weeks ago. No change.

What's the next step here? I don't have a lot of electrical know-how or tools, but I'd like to avoid an expensive trip to the dealer.

 
Rep Power: 224

Could be the compressor clutch. It wears down and eventually begins to slip, this generates heat. After a few minutes it will get hot enough to trip the thermal switch to prevent damage. A/C will begin working again after the compressor has cooled down.

 
Rep Power: 0

Gotcha. That sounds like a new compressor.

 
Rep Power: 222

You can replace the clutch and coil without replacing the compressor. Potentially you might just need to take a shim out. The system doesn't need to be evacuated.
check on rockauto. I did this on my 2000 last week.