How to keep blower on after a/c shuts off

[Needaclue]

Looking for an easy cheap way to to do as title says. The A/C compressor and the blower turn off simultaneously leaving a fair amount of cooling left in the evaporator. A thermometer at the first vent from the HVAC shows 45 degrees at shut off. Manually setting the blower on for 7 minutes brings the temp up to 65. I'm looking for a way to do this automatically. This is a 25 year old Heir furnace and Tempstar A/C condenser. Looking in the manuals and at the furnace I see no adjustments to make this happen. Any ideas?

[HayZee518]

look on the unit and in the schematic for an evaporator fan relay. now look in an electrical catalog for a pneumatic control relay. this type of relay uses an electromagnet to open/close a circuit initially but the contacts open or close after a pneumatic time delay. the contacts are referred to as an A or B contact depending on usage. check your unit's control circuit voltage - i.e. 120 volts or 24 volts. whichever it is buy a pneumatic control relay with the same voltage rating 120 volt or 24 volt. amperage would be negligible.

[Needaclue]

Thanks for the quick response. "Pneumatic" meaning air sensing. What air would it sense and where would it connect to the air source?

Did more poking around. Control circuit uses 24 volts. Do you think this gadget would work? Blower Control | Delay Timer | ICM Controls

[HayZee518]

the "air" is atmospheric air. whatever surrounds the relay. no air source needed. inside is a diaphragm that is actuated by the magnet and opens the diaphragm. other side of the diaphragm has a switch on it. when power is disconnected to the relay a spring tries to close the relay but the air has to pass through a variable orifice before the contacts will close or open. hence the time delay.