A/C evaporator seal foam blocks bypass air. It seals the gaps between the evaporator core and the plastic case. This forces all air from the blower motor to flow through the cooling fins rather than around the sides. The foam also cushions the core to prevent rattling.
Mechanic Glossary
A/C Evaporator Seal Foam
Adhesive foam strips wrapped around the edges of the evaporator core to seal the gap between the core and the housing box.
Frequently Asked Questions
It ensures maximum cooling efficiency. Without the foam seal, up to 20% of the air would bypass the core, blowing warm air into the cabin.
Small black foam particles will blow out of your dashboard vents, and A/C cooling performance will drop slightly.
Yes. New evaporators usually come with adhesive-backed foam strips that you must wrap around the core edges before installing it.