How to replace Air conditioner relay switch?

Only way to tell if A/C Evaporator Core Orifice tube is plugged is by looking at A/C gauge readings , An if it is plugged you more then likely need a new compressor , they become plugged with metal particles from worn out compressor. Your best bet would be to take your vehicle to a qualified repair shop .

#46-12-03: AIR CONDITIONER BLOWS WARM AIR (REPLACE A/C DELAY RELAY) - (Apr 7, 1994) REVISION: 04/14/94
THIS BULLETIN IS BEING REVISED TO CORRECT THE TRANSMISSION LISTED IN THE MODELS. ----------------------------------------------------------------------
SUBJECT: AIR CONDITIONER BLOWS WARM AIR (REPLACE A/C DELAY RELAY)
MODELS: 1994 CHEVROLET AND GMC TRUCK S/T PICKUP WITH 4.3 ENGINE (VIN Z - RPO LB4), 4L60E TRANSMISSION (M30) AND AIR CONDITIONER/MANUAL CONTROLS (C60); OR 4.3 ENGINE (VIN W - RPO L35) AND A/C (C60)
BUILT BEFORE THE FOLLOWING VIN BREAKPOINTS:
PLANT DIVISION VIN LINDEN GMC RK501034 SHREVEPORT GMC R8501199 SHREVEPORT CHEVROLET R8105893 LINDEN CHEVROLET RK103097
CONDITION:
SOME OWNERS MAY EXPERIENCE A CONDITION WHERE THE AIR CONDITIONER IS TURNED ON AND DELIVERS ONLY WARM AIR.
CAUSE:
THE AIR CONDITIONER COMPRESSOR MAY DELAY LONGER THAN THE "ORIGINAL DESIGN" INTENDED 12 SECONDS, OR MAY NOT ENGAGE, DUE TO THE POSSIBLE MALFUNCTION OF THE COMPRESSOR DELAY RELAY.
CORRECTION:
TRUCKS BUILT BEFORE THE VIN BREAKPOINTS LISTED ABOVE MAY NEED A NEW AIR CONDITIONER DELAY RELAY. REPLACE ONLY WITH 15990540 AIR CONDITIONER COMPRESSOR DELAY RELAY. SPECIFIED PROCEDURE IN SERVICE MANUAL NATP 9429, PAGE 1B-59. TEST AIR CONDITIONER OPERATION FOR DELIVERY OF COOL AIR.
NOTE:TO TEST FOR PROPER OPERATION, PUT THE A/C CONTROL ON THE "OFF" POSITION, START THE ENGINE, THEN PLACE THE A/C CONTROL IN THE "ON" POSITION. THIS SEQUENCE WILL PROVIDE IMMEDIATE ENGAGEMENT OF THE AIR CONDITIONER COMPRESSOR. WHEN THE ENGINE IS STARTED WITH THE A/C CONTROL ALREADY "ON", THERE WILL BE A NORMAL 15.0 SECOND DELAY FOR THE AIR CONDITIONER TO ENGAGE.
SERVICE PARTS INFORMATION:
P/N DESCRIPTION QTY
15990540 A/C COMPRESSOR DELAY RELAY 1
PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

Air Conditioner No air coming from air conditioning vents

1. Check the air conditioner fuse and replace as necessary.
2. Air conditioner system discharged. Have the system evacuated, charged and leak tested by an MVAC certified technician, utilizing approved recovery/recycling equipment. Repair as necessary.
3. Air conditioner low pressure switch defective. Replace switch.
4. Air conditioner fan resistor pack defective. Replace resistor pack.
5. Loose connection, broken wiring or defective air conditioner relay in air conditioning electrical circuit. Repair wiring or replace relay as necessary.

1. Check the air conditioner fuse and replace as necessary.
2. Air conditioner system discharged. Have the system evacuated, charged and leak tested by an MVAC certified technician, utilizing approved recovery/recycling equipment. Repair as necessary.
3. Air conditioner low pressure switch defective. Replace switch.
4. Air conditioner fan resistor pack defective. Replace resistor pack.
5. Loose connection, broken wiring or defective air conditioner relay in air conditioning electrical circuit. Repair wiring or replace relay as necessary.

1. Check the air conditioner fuse and replace as necessary.
2. Air conditioner system discharged. Have the system evacuated, charged and leak tested by an MVAC certified technician, utilizing approved recovery/recycling equipment. Repair as necessary.
3. Air conditioner low pressure switch defective. Replace switch.
4. Air conditioner fan resistor pack defective. Replace resistor pack.
5. Loose connection, broken wiring or defective air conditioner relay in air conditioning electrical circuit. Repair wiring or replace relay as necessary.

This is a common problem on all Astro/Safari vans. The problem is a leak in the vaccum lines that control the vaccum switch responsible for changing air direction from the defrosters, dash vents, floor vents..etc.
Many of the problems that plaque the Astro/Sarfari vans and many other "Mini-Vans" is the build up of excess heat in the engine compartment. It\'s a tight place to put a V6-4.3 Vortec engine and the heat generated bounces back and cooks everything on the engine (coils, modules, sensors, wiring, and of course plastic vaccum hoses). No need to mess with your switches or anything behind the dash -- replace those thin plastic vaccum hoses to operate the vaccum switch (located just below the A/C canisters, to the right of the heater/ac blower housing) and your dash switches will magically send heated or cooled air where you want it.

No air coming from air conditioning vents

1. Check the air conditioner fuse and replace as necessary.
2. Air conditioner system discharged. Have the system evacuated, charged and leak tested by an MVAC certified technician, utilizing approved recovery/recycling equipment. Repair as necessary.
3. Air conditioner low pressure switch defective. Replace switch.
4. Air conditioner fan resistor pack defective. Replace resistor pack.
5. Loose connection, broken wiring or defective air conditioner relay in air conditioning electrical circuit. Repair wiring or replace relay as necessary. Air conditioner has a smell when used
   1. The air conditioner evaporator drain hose is blocked or partially restricted, allowing condensation to build up around the evaporator and drainage tray. Clear the drain hose where it exits the passenger compartment.
   2. Check compressor clutch wiring, electrical connections and compressor clutch, and repair or replace as necessary.

o air coming from air conditioning vents

1. Check the air conditioner fuse and replace as necessary.
2. Air conditioner system discharged. Have the system evacuated, charged and leak tested by an MVAC certified technician, utilizing approved recovery/recycling equipment. Repair as necessary.
3. Air conditioner low pressure switch defective. Replace switch.
4. Air conditioner fan resistor pack defective. Replace resistor pack.
5. Loose connection, broken wiring or defective air conditioner relay in air conditioning electrical circuit. Repair wiring or replace relay as necessary.

Sounds like a bad heater control unit, or bad control module. You are bypassing the switch when you jump the relays, so usaully the switching mechanism is suspect.

replace the air conditioner relay, its located underneath the hood, you will see the relay center there, look underneath the cap to identify which is the ac relay switch.