Had a little time today to check air flow. Air is blowing out of vents inside car. Air is sucking in at grill under wipers on outside of car. Do they make a metering device to check how much freon you put in a system using a 30lb canister?

The metering device would be a scale used during the charging process.

BTW, doesn't that car have a sight glass?

Fresh Air Door
 

Checked the Air door behind the glove box today. It does not close with temp wheel in min position. When I press the recirculate button it does not close either. I closed it and put a small block of wood against the frame to hold it. The outside temp is 72. At idle the air temp coming from the center vents is 62. I ran it at 2000 rpm's for 5 minutes and the air temp coming from the vents is 58. It looks as though there are 2 vacuum servos attached to the air door. This car does have a sight glass and at idle there is almost a constant flow of freon. It does have a gap in the flow sometimes. The flow is white looking. I am going to remove the blower on Sat and inspect the evap core. Thanks for all the help.

There is no vacuum to the servos at the air door behind the glove box. All the other doors work. What should I check first? I will be ordering a freon scale and will remove the freon from the car and recharge. My specs say to use 2.2 lbs of R12 freon. If I use R134a should I charge 80% of 2.2 lbs?

Yes, use 80% of the R12 spec when substituting R134a.

Clogged a/c drain in'91 300E
 

Good to know! And now I won't go crazy searching for non-existent filters😁 (but still with original problem of locating probable clog...!)