What your describing is exactly what I was experiencing in my 85. I thought the ducts were bleeding air. So I got some aluminized duct tape and sealed everything up.
I mean every where there was a seam in the stock ducting got it covered with tape. NO difference to air volume at MAX setting.
Replaced blower motor with new hundred dollar Napa part seen some junk in the bottom of the air box under the blower and cleaned it out and washed the squirrel cage thoroughly. ZERO difference.
Thought maybe there was a problem with the A/C since I had it converted to R-134. Had the MOST reputable shop in the area take a quick look at all the system pressures and condition which were ideal. then even had them evacuate and recharge system and recheck pressures again they were stellar. NO difference in cold air volume.
Finally after sweating in the hot sun in traffic one day I got pissed enough to Check the ONE thing I had not actually laid my own eyes on which was the A/C evaporator. LOW and behold there was about 2 sq. inches of fins that were actually letting air pass through. every other nook and cranny of the evaporator was PLUGGED SOLID with grime, grit, dust, oat chaff, horse hair, saw dust, even some remnants of packing peanuts and a number of other F. O. D. that was picked up by the Max A/C inlet under the glove box near the passengers feet. Where all the dust and junk from working in the field or out at the ranch would collect.
pulled the evaporator out not draining the system just using the slack in the lines and laid it on the fender well and flushed it using the hose at about 1/4 power and back flushing both ways till water flowed freely through it. then hit it with some simple green and let that soak for 3-5 min then flushed thoroughly again. cleaned out the area in the box near the evaporator with a vacuum and a wet rag. Thoroughly cleaned the evaporator drain and put it back together with a LIGHT bead of silicone to seal the box tight and low and behold TONS OF ICE COLD AIR!
IM willing to send you $10 cash if that's not your problem! That's how confident I am that it is.
there's a company out of AZ that is a Internet dealer in A/C system parts and what not. I think I got there web address from Warden when he was looking to install a parallel flow condenser for his R134 retrofit. Any way they have a foaming cleaner that works pretty well on moderately dirty systems. You drill a SMALL i think 3/16" hole in the heater box in front of the evaporator and insert the dispensing nozzle hooked to the aerosol foam can empty contents into air box while running the ac on Max high and watch all the sludge and grime come out of the drain hole. As I recall it was pretty cheep too. Did that on my 94 and it helped a bunch.
