"bizarre" a/c behavior

2014 honda civic LX 1.8L engine, 117,000 miles
engine is running, vehicle stationary, hood up, ambient outside temperature 90degrees

compressor turning, clutch engaged;
compressor clutch does not ever disengage during any of the following
and the condenser fan itself also turns continuously during all of the following ;
pressure at low-side port wobbles a bit around 40 psi value

PLENTY OF VERY COLD AIR INSIDE CAR AT THE VENTS

shortly after engaging a/c from within the vehicle, here is what happens:
there a thumping/rumbling noise from the condenser fan area,
and a large blast of very hot air shoots out towards rear of engine;
the noise and air blast last for about 10 seconds; the both stop for about 10 seconds;
then both occur together again for 10 seconds; then off for about 10 seconds,
- over and over ; (after a couple minutes of this, i turn a/c off)

what is the cause of this periodic, repetitive, off-and-on rumbling noise and air blast
( i say again: the condenser fan does NOT stop-and-start during any of this) ?
(I've consulted the Haynes manual but nothing in there corresponds to anything quite like this)

thank you

 

We need to see what the high side is doing. If the clutch stays engaged the pressure should be extreme and the pop off will blow.
What is the static pressure?

 

my gauge/dial attaches only to the low-side port; its value while all of the aforementioned is going on is 25

 

With everything off what is the pressure? That is static pressure.

 

that's with fan ON and a/c ON -- and cold air is coming out of the vents ;;
with everything OFF (engine off, fan off a/c off ) pressure is 80++

 

That's normal static pressure. Need to get a gauge on the high side.

 

ah .... ok ;; i guess that's my next task
thank you, so far