1995 E320 A/C blower testing
 

At highway speed very slight air coming thru the vents is cold with the A/C on but otherwise no airflow so I suspect the problem is a bad blower or regulator.

To do the first basic test, I understand I need to check voltage at firewall from yellow>blk and red>blk.
WHERE?
I traced the A/C fuse wire on the strut mount and it branches off - one to the firewall behind the brake booster (no connector, just straight thru the firewall) the other goes to a 3 pin connector at the top of the wall separating the engine area from the firewall area. The wires in that connector are not black, yellow and red. they are red/green stripe, brown and another set of stripes (getting dark outside, can't tell). I tested left pin to middle and got 0. I tested middle to right pin and got 0. I don't even know if this is the correct wires to test.
With this connector unplugged with key turned on but engine not running I got loud hissing noise from the Aux air pump area (warm up air pump) .
Someone please give me a clue where to test before I rip everything open to get access to the blower.

The blower motor connector is on the left outside firewall (sort of near the brake fluid reservoir), it sounds like you found it already. Just jump power and ground to the connector ON the firewall and see if the blower fan then runs. OR if you want to do it the opposite way, turn the key on and turn the climate control to defrost mode and check the HARNESS side, in defrost mode you should have high speed fan and therefore should have battery voltage if you want to test with a voltmeter. I assume the strip fuse on the left strut tower is not burnt out or cracked?
Gilly

The fuse on strut tower is solid, no trace of burns or cracks. the fuse in the relay (item B in the relay box behind main fuse box) is good.
At the crack of dawn I'll test the pins with defroster on.
thanks for your input

I went to test 3 pin connector this morning, turned key in ignition and pushed defroster button...and the fan started blowing.
So what ever it was that was causing blower not to work is ....
INTERMITTENT!
I hate intermittent.
You never know when you really fixed it becuase you replace one part, try the system and it works....and then it doesn't work. So you end up changing mutiple parts.

sampling motor that pulls air across temp sensor at the dome light can cause what you say, or a weak/dying regulator.

That's totally like "headline news" for me, never heard of such a thing.....

MORE than likely it's the brushes worn out on the blower motor itself.

Gilly