jjbjr64

I'm replacing the AC Manifold that bolts to the air conditioner under dash, There is a hole in it. (see picture attached). have no idea what this is for. Can anyone enlighten me. Thanks.

AZ442

I have no idea why, I pluged mine.

defiant1

Is there a drain hose that attaches to the a/c that would feed down through that hole?? I don't have the same set up, but an 1970 aftermarket version that I had to run a hose outside the firewall.

d1

jjbjr64

I don't think there is a drain hose involved, cause it is facing the dash not the firewall.

fjross

My car is a 71 and it also had a casting hole from the factory in the plastic plenum. I thought it was a hole made by the previous owner, but when I checked other 71 plenum's, they had the same hole in same location.

Lady72nRob71

I know what you are talking about, I was wondering that myself. Not a drain - too high up, away from the evap. Also the manifold is not sealed well to the heater box - 2 screws and tape...

All I could think is that it is a little unmentioned vent to create a small draft down there when the fan is on. I once though it could have been for a sensor or switch that was never used, but I would expect some mounting holes near it.

69442C

Maybe it was there as a pressure relief so when a vent was closed there would be a means of a little pressure escaping so the ductwork wouldn't try to move around. Maybe it solves a problem of air hammer like would be seen with water hammer at home when a faucet is closed quickly.

Or, maybe an inspection port to allow someone to see if the damper door was moving. But you would think a removable plug would be in that hole if this was the purpose.

Or, maybe the the designers knew that some of these cars would eventually sit for very extended periods of time and eventually become a home for mice and other critters. This opening just was a means give to those critters complete access to the ductwork system too.

Lady72nRob71

Engineers put it there so toddlers could have something to get their fingers stuck in.