On a 1994 base corvette C4 equipped with electronic air C68 system. The compressor and blower motor run when the heater and A/C Control Head blower mode is on "OFF! Air flows through Def Vents but not through the air vents. The only way to turn off the Compressor is to remove the fuse. The blower is new. Please advise!

Edward,

C4 Corvettes have an Outside Air Temperature sensor which may be faulty. It senses air temp in front of the car and tells the climate control unit (which controls the heat/ac) what the temp outside is. Yours is in front of the grill. It's a $20 part. It looks like the attached link. I'm not sure if this is your issue, but it was on my son's car. I just thought it might give you a direction to check.

Fred-
C4 Corvette 1986 1989 Outside Air Temperature Sensor

no it does not. The heater system works from a small radiator in side the cabin in a box with the blower motor. The compressor runs off the motor and is responsible for the cold air in the cabin. You may be confused because in climate control vehicles the compressor is running all the time and you vary the cold air by opening up the tap to the heater core in side thecar

unplug blower run hot wire to blower see if it works if does it resistor nif not it blower

The first thing to do here is test the blower motor, it may have worn out brushes. Make up a jumper cable from bulk lamp cord (avail, from any hardware store by the foot) and connect it to the battery and then to the blower, if it doesn't run tap it with a hammer handle, if it starts the brushes are the problem and you need a new blower motor.

If this is electronic system with digital readout, it is likely the control head or blower motor speed controller. I think your owner manual tells you how to self test control head. go to car-part.com to find used part. or tascafordparts.com for new at discount.

When the engine is cold,check the coolant level.

Make sure it's on max.

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A coolant system should be flush every two years.

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If you did a coolant flush recently then air pocket can be the cause of the un-even heating problem.

The DIY method is to drive you car onto a ramp or a steep hill.

Iet the engine cool off and top off the coolant tank.

Set MAX heat + MAX fan

Let the engine ran for 20 minutes wih the cap off and the trap air will escape from the coolant reserve tank,

Check coolant level and top off coolant when the engine cools down.



A shop will charge $75+ for this but using an air operated excavate tool!

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A car with over 90K miles may experience linkage problem to the heater control valve.

The heater control valve (near the firewall) may be stick over time.

Open the hood and move the heater to max and min. Back and forth.

Clean and lube the linkage with WD-40 to free the heater control valve.

If it's a vacuum type heater control valve then cash for leaky vac. hoses.


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Move the fan switch back and forth to re-new the electrical conductors.

Pass a vacuum over the control panel to prevent dust build up behind the console.

Is the heater working? Turn the A.C. off with the car at an idle. Turn the A.C. on and listen for the compressor to turn on. (should hear a click under the hood and the motor should change pitch. If no noise, the compressor is not comming on. The o-rings were bad about leaking on these cars, letting out all the freeon. If there is no freeon, the low pressure switch won't let the compressor run.

ok could be one of 3 things. 1 you may be out of freon. (proly spelt that wrong) 2. compresser could be bad. 3 the clutch on your compresser might not be engaging. when trucks running turn ac on and see if the front of your compresser spins or not. if it does clutch is good. but it could be that your compresser is still bad. either way i recomend you go for freon and start there. when they fill it they will tell you for sure wether or not your compresser is bad.

The temp blend door rotates between allowing heat through the heater core, or cold air through the a/cevaporator, or a blending of the 2 by being anywhere between the two.

I would check the heater a/c control head first and hope it's just the control head.
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here is a descripton of the system.

Section 12-03A: Air Conditioning, Heater System, Manual, Ranger and Explorer 1996 Ranger and Explorer Workshop Manual
DESCRIPTION AND OPERATION A/C-Heater System, Manual The manual air conditioning/heater system used in these vehicles is a split-case, blend air design. This design includes the following major components:

• An A/C evaporator housing (19850) which is attached to the engine compartment side of the dash panel (01610). This assembly includes: (1) the A/C evaporator core (19860), (2) the suction accumulator/drier (19C836), (3) the A/C cycling switch (19E561), (4) an internal, A/C evaporator core orifice (19D990) located inside the inlet line to the A/C evaporator core, (5) a blower motor (18527), (6) a blower motor wheel (18504), (7) a heater blower motor switch resistor (18591), and (8) the A/C evaporator case (19897).
• A heater air plenum chamber (18471) which attaches to the passenger compartment side of the dash panel. This assembly includes: (1) the outside/recirculating air inlet door, (2) the panel door, (3) the floor defrost door, (4) the temperature blend door, and (5) the heater core (18476).
• Other components which link and/or control the heating and air conditioning systems include: (1) the A/C control (19980), (2) the ducts and registers, (3) the windshield defroster hose nozzle (18490), (4) the control cables, (5) the vacuum lines, (6) the refrigerant tubes and hoses, (7) the A/C compressor (19703), and (8) the A/C condenser core (19712).

The A/C control (19980) assembly consists of three main parts:

• The function selector knob, a vacuum selector valve combined with an internal electrical switch.
• Heater blower motor switch (18578), an electrical switch that provides four speeds of A/C blower motor operation.
• A temperature control knob, which controls the position of the temperature blend door mounted on A/C evaporator housing (19850) assembly.

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Temperature Control
The temperature selector actuates a variable resistance switch. This switch varies the voltage to an electric actuator used to position the temperature blend door. Positioning the temperature control in any position between COOL and WARM causes the temperature blend door to direct more or less outside air through or around the heater core (18476) for whatever proportion of heated or unheated outside air is desired. The air blends together as it leaves the heater core and enters the heater air plenum chamber (18471) for distribution.
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System Airflow Description Air is drawn into the system by the blower motor (18527) through the outside-recirc. door opening. The air is blown through the A/C evaporator core (19860) and then the heater core (18476) (when the temperature control is moved toward the WARM position). When the temperature blend door is in the maximum COOL position, the air bypasses the heater core. When the temperature control is moved to the right, away from the maximum COOL position, air passes through the heater core where it is warmed, and then mixed with the cool air before it is discharged through the registers. OFF
With the function selector in the OFF position, the outside-recirc. door is in the recirculated air position. It is closed to outside air and no air passes through the system. The blower motor is off. MAX A/C
NOTE: No temperature modulation is possible in the MAX A/C position.

In the MAX A/C position, the outside-recirc. air door is in the recirculated air position. All of the air discharges through the panel registers except for a small amount of floor bleed. The A/C compressor (19703) operates in this function control setting.
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You have to almost remove the dash to get this part out.
Removal

1. Disconnect battery ground cable.
   

1. NOTE: Refer to Section 01-12 for instrument panel removal and installation procedure.
   
   Loosen instrument panel (04320) and pull back from cowl.
   

1. Remove A/C electronic door actuator motor electrical connector from bracket on A/C evaporator housing.
   

1. Remove three A/C electronic door actuator motor retaining screws.
   

1. NOTE: The mounting bracket remains in place on the A/C evaporator housing.
   
   Lift A/C electronic door actuator motor vertically approximately 12mm (1/2 inch) to disengage it from bracket and actuator shaft, then pull A/C electronic door actuator motor back toward passenger compartment.
   

Notes Electronic Automatic (RPO C68)/ Dual Zone Air Conditioning (RPO CJ2)