I have the Pisa Euro dash in my 88 Mera. I finally got the AC working and found that on MAX and NORM cold air only comes out of the side vents and does not cool the cabin very well. Switching the AC to bi-level does a little better but doesn't recirculate cabin air so it's still marginal cooling. I wanted to have AC air come out of the three round vents on the top of the dash.

I pulled the dash to see how the Pisa plenum worked and what I could do to get better airflow and cooling. I drilled three 1 1/2" holes in the plenum between the upper and lower chambers. Now I get AC air out of the three top vents and defroster vents also. The airflow out of the side vents is about the same as it was before I modified the plenum so there is at least double the airflow in all the AC control modes. So far having cool air coming out of the defroster vents has not been a problem but if one shows up I will just block them off.

I don't know how this modification will affect the HEAT and DEFROST modes when it's cold. I don't drive it in the winter so for me that isn't a concern, I just want to be comfortable when it's hot.

quote Originally posted by Larryinkc: I have the Pisa Euro dash in my 88 Mera. I finally got the AC working and found that on MAX and NORM cold air only comes out of the side vents and does not cool the cabin very well. Switching the AC to bi-level does a little better but doesn't recirculate cabin air so it's still marginal cooling. I wanted to have AC air come out of the three round vents on the top of the dash. I pulled the dash to see how the Pisa plenum worked and what I could do to get better airflow and cooling. I drilled three 1 1/2" holes in the plenum between the upper and lower chambers. Now I get AC air out of the three top vents and defroster vents also. The airflow out of the side vents is about the same as it was before I modified the plenum so there is at least double the airflow in all the AC control modes. So far having cool air coming out of the defroster vents has not been a problem but if one shows up I will just block them off. I don't know how this modification will affect the HEAT and DEFROST modes when it's cold. I don't drive it in the winter so for me that isn't a concern, I just want to be comfortable when it's hot.

I'd be interested to know what testing PISA had done when they designed this. My guess is that it was more of an aesthetic look than really a technical one, so I don't suspect it will have too much of an effect on defrost... you've probably improved it overall.