Heater only blows from defroster

Car is a 97 3.8 and the other day I switched the defroster on to clear some moisture on the inside of the windshield. Now the heater or a/c only blows from the defroster vents. The a/c shuts off when I switch to heat but still blows from the top.

It looks like the system is controlled by vacuum. I have good vacuum at the intake and I can trace the vacuum line to the firewall. Does anyone know where this line comes through? Behind the heater blower maybe?

Anyone had a problem with this? Is there a cable connection from the switch on the center dash or is this strictly vacuum controlled?

Thanks,
Gary

telmd said:

I had a similar prob on my 94. On mine it was the vac line that comes thru the firewall had a slit in it causing it to leak. took a peice of rubber vac line and a couple zipties and patched it up....been working fine every since

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Do you know where that vacuum line goes, once it passes through the firewall?