I have a 1998 Taurus I just got from Grandma. It is a creampuff with only 86k on the ticker. Had to replace the fuel pump, filter, plugs, and wires to get it running. Recharged the AC, and got it frosty. Problem is, under acceleration the output changes from vents to defrost. I used a can of starter fluid, spraying all over the engine bay while at idle, trying to find a vacuum leak, no luck. I got online and learned the culprit is most likely the HVAC vacuum check valve. Ordered it yesterday, got it today, put it on, and no change. It still changes to defrost under acceleration. Any ideas on where else I should check?