Originally Posted by Aage
Do the old Armstrong units have high and low Schrader valves?
Only low, which is usually at the back end of the AC.
A proper working roof AC, should kick up the high pressure, to 4 times the low pressure.
As an example, if the low is 70 psi, the high should be 280 psi.
A good indication of a worn out compressor is when the 4 times, starts dropping, to even 3 times.
That's a positive indicator that the compressor is worn out.
Compressors don't last forever.