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You are getting excellent advice on troubleshooting your problem.  As Richard suggests, do yourself a huge favor and acquire a decent meter that checks capacitance, that would be my first immediate step.  You may have more than one failure point.

My experience in general FWIW, regarding A/C parts causing failures. I have changed a couple hundred condenser fan capacitors, a few dozen condenser fans, a dozen or two thermostats with the relatively small group of units maintained over the last 30 years.  On a normal R22/R410 household A/C unit, if the condenser fan quits the compressor internal thermal switch will overheat and shut the compressor off in a matter of seconds.  If the condenser fan shaft sleeve/bearing is bad or needing lubrication the fan will lose RPM, most are 825 or 1075RPM, raising the compressor temperature etc., etc..  I have seen the evaporator turn into a block of ice that took all day to melt on a 115ºF day due to a dirty condenser.  A capacitor has a 5% tolerance, anything outside of that range can cause a variety of problems with the fan motor, intermittent or not running at all.  The motor capacitor needed is specified on the tag attached to the motor.  There is always the possibility someone installed an incorrect size capacitor, check the tag.  Most old A/C units were made for the cheapest air filters with good airflow.  Do not use the HEPA or pleated filters designed to clean your air, they restrict airflow causing the fan to work harder causing the compressor to run warmer causing the pressures to be higher causing the refrigerant system to be inefficient and eventually causing the evaporator to become a block of ice.    Newer systems were made for those filters.

This week I will be checking all A/C units capacitors, motors etc..  Most techs do an amp check on the fan motor, I use a screwdriver to spin the condenser fan.  If it doesn't keep spinning freely I replace the motor.  I try to avoid having those phone calls at 3PM on a 118º day.

Most problems are within your capability, keep at it!

From what I understand the only filters are under the entry steps??  Or are there some elsewhere??

Mine are under the stairs. Only way to get to my coils on the units to clean them is to pull the unit. Suspect its the same for yours. Mine were actually not that dirty, I was surprised especially since there was dust almost in all the bays from being taken out west, there was even sediment in the water filter I had to clean out.