Another A/C question

[Navy Flier]

We have not had to use the dash air until we got into August so this problem was late in surfacing. A/C works ok on Norm but when I switch to Max the air ceases to come out of the dash vents and is diverted to the defroster vents. It is still cold, just blowing out of the wrong vents. Switching back to Norm results in air from the dash vents again. Intuition tells me that for some reason one or more plenum doors are not operating normally. Any other ideas?

As an aside, an A/C tech told me that having the blower on the max setting blows air that is not as cold as turning the blower down one notch. He said on max the air passes over the coils too fast to cool properly. I tried turning the blower down one position and sure enough it was colder. It means to me that the max setting would be good for initial cooling and then turn it down to maintain the temp.

[Navy Flier]

We have not had to use the dash air until we got into August so this problem was late in surfacing. A/C works ok on Norm but when I switch to Max the air ceases to come out of the dash vents and is diverted to the defroster vents. It is still cold, just blowing out of the wrong vents. Switching back to Norm results in air from the dash vents again. Intuition tells me that for some reason one or more plenum doors are not operating normally. Any other ideas?

As an aside, an A/C tech told me that having the blower on the max setting blows air that is not as cold as turning the blower down one notch. He said on max the air passes over the coils too fast to cool properly. I tried turning the blower down one position and sure enough it was colder. It means to me that the max setting would be good for initial cooling and then turn it down to maintain the temp.

[garybtt]

Check your vacuum pump and see if it is working.

["007"]

Check also the vac-tubes coming of control unit.

[tomsm]

Navy Flier - there was a very good thread on this problem a few weeks ago - pictures and everything...