My AC is blowing but cooling intermittently (not cooling at when idling). on 1994 Volvo 850

The AC is cooling but weakly when driving.
I had an AC sealer put in and the coolant filled.
It is performing a bit better now. Before filling it stopped cooling all together.
I recently had the timing belt and water pump replaced.
Someone said that this could be an AC thermostat (near pump) problem.
I was also told that this is may be compressor problem (bad clutch) and need the compressor and dryer replaced.
Could it be a faulty sensor?
Will diagnostic codes point to a solution?

3 answers 4 comments
You might have a dirty condenser coil or blockage between the radiator and the coil. This would not let air flow through to help cool the coil, when you are driving more air gets through and as the coil cools so does the air in your vents. But there are several other problems that could cause the same result, like a weak compressor, blockage at orfice tube or expansion valve. You really need to have a performance test done on the system to pin point the problem. Just adding freon yourself or scanning for codes will cure this problem. Replacing the A/C clutch doesn't require replacement of the dryer but replacing the compressor does.
Sounds like many good points.
I'll have to check them out and respond.

most likely u have a leak and are wasting money on freon. the sealer is a temp fix at best. find the leak w/ a/c leak dye and repair as req.
I do have a leak but it is tiny.
I filled the freon 2 years ago and it has worked fine since then.
I believe that the current filling and seal should have resolve the leak problem.
ok then poss air flow or freon flow have that ck'd out
Air flow is strong. Sealer was just put in and freon was topped.
If the freon level is good (A/C clutch is not cycling on and off all the time) and airflow is continuous (the fan is not shutting off), then I would check to see that the A/C clutch is engaged when it is acting up. It's common for the clutch to shut off when it warms up, probably from an open electrical circuit inside the clutch.