A/C airflow drops when accelerating or going up a hill

[JCurtis]

I have a 96 Bonneville that needs some A/C work.

Seems that when you are at highway speed and accelerate or go up grade the airflow through the A/C vents drops to almost nothing... then pics up again when you slow down or level out.

This is really annoying... A/C shops say they can't find anything wrong.

It never did this when it was new. I have replaced the compressor and other items that have failed, and it goes into the shop soon to get the orifice tube unplugged and the system recharged because its blowing warm air.

Any suggestions about the disappearing airflow?

And why does the orifice tube get clogged so often?

[Flatrater]

Orfice tubes get clogged by metal coming from the compressor. I always replace the orfice tube every time I replace a compressor. The tube is pretty cheap to replace.

As for your airflow I suspect you have a vaccum operated HVAC doors at open throttle you loose vaccum and the doors go towards default mode which is air blowing on the windshield in defrost mode. I would look at the vaccum source making sure the line is attached and no cracks in the vaccum tank. After that check make sure the vaccum check valve is working.

[JCurtis]

Okay, I have the air blowing cold again, but I still have the problem with disappearing air flow under acceleration and going up hill under acceleration.

Any other suggestions as to where these alleged vacuum leaks might be and how I can locate?

Originally Posted by Flatrater

Orfice tubes get clogged by metal coming from the compressor. I always replace the orfice tube every time I replace a compressor. The tube is pretty cheap to replace.

As for your airflow I suspect you have a vaccum operated HVAC doors at open throttle you loose vaccum and the doors go towards default mode which is air blowing on the windshield in defrost mode. I would look at the vaccum source making sure the line is attached and no cracks in the vaccum tank. After that check make sure the vaccum check valve is working.

[jbh49]

Had the same problem on my '97. Replaced the vaccum lines and had to replace the valve controlling the door that directs the air...like what Flatrater said.

[Telepath]

The line to your vaccum tank might be cracked or loose. The tank is under the passenger front quarter panel, kinda below and behind the headlight. The hose on my Bonne was rather brittle and weathered, and the car behaved exactly like you described. Repair or replace the hose and your problem will likely go away.