Air Con Not working - Fan working fine - any advice?

Aircon will not not engage if low gas.

The light not illuminating could be as simple as a bulb - I am unsure of the switch system so best to get other advice.

Wanted to offer advice of if you want good aircon, after twenty years of the system running, maybe time for a clean and system refurbishment;
Get the system professionally degassed
Remove the ac evaporator (undo the two pipes in the front trunk infront of passengers side foot well area / next to battery, then the four screws under the dash) then wash with dishwashing liquid and warm water. Washing is just putting water over, it's delicate like a radiator/intercooler.
Replace the Tx valve whilst the evaporator is out (estimated part cost under $100)
Replace all connection pipe Orings (cheap as but time consuming)
When getting it regased, get the a/c shop to change the dehumidifier canister (estimated part cost $30)
The above costs a bit more but can make a big difference on the a/c performance, longevity, and smell :)