A malfunctioning cabin temperature control system required further investigation.

There are days when we make repairs that, complex and simple at the same time, bring us a high level of satisfaction and pride as technicians. Take for example, this repair we did on a 1989 Corvette convertible.

The customer complaint: the automatic heating and air conditioning system does not seem to be able to maintain the desired temperature in the cabin.

In the cold

At our first check, we can very well observe that if we set the desired temperature to the warmest, the temperature of the air leaving the ventilation system remains very cold. We can’t have heat. Before looking further, since this is an electronically controlled system, the first task would be to check for trouble codes.

In 1989, we are asked to press “Ext Temp” and “Auto” so that the module shows us the codes present. Please note that if this maneuver does not work, you have not selected the correct “Auto” button. No code present for the moment. In this situation, we go to the “symptom testing” chart, and we go down to “temperature of air discharged from vents is incorrect, no fault codes” which takes us to the test chart A: Heater and A/C Programmer.

This first series of tests makes us check the power supply and the ground of the module that controls the different vacuum valves for the direction of the ventilation and the temperature actuator. All pass the test, so we move on to Table 2. This is where the problem lies. Here we have to check the power supply of the temperature actuator and the integrity of the wires. The 12 V power supply is not there. This conclusion leads us to Table 4. This table makes us complete a final check to confirm that the module is really in default, which is the case.

Inside the module

Since the room is not available, we decide to open the module (A/C Programmer), to see if there is anything we can do. It is here that we can see that two solder joints on the circuit board are compromised. Two small welds were enough to make the system operational as in 1989.

A customer more than happy to have his Corvette repaired, just in time for the summer season!

Steve Oborne is the owner, with his wife Jennifer Gilbert, of Atelier Oborne Service in Val-Joli, QC. He has been involved in mechanics since his childhood. [email protected].