Modern automotive heating, ventilation, and air conditioning systems (HVAC), use an electronic control module which is much like an electronic thermostat inside of a house. What makes it different, however, is that the module in a house is a simple thermostat which sets the temperature. In a vehicle, the control module sets the temperature for up to four zones, controls the amount, temperature, and location of air flow, and controls the operation of the refrigerant system in the engine compartment. This is a might task, but it is all cone by a small microprocessor.
How do HVAC Electronic Control Modules work?
The HVAC electronic control module receives input from many areas to determine the best method of accomplishing the task of bringing comfort to the passengers inside the vehicle. When it receives information, it compares that information to programmed tables and graphs, and follows pre-set instructions on how to perform its' job. Inputs range from ambient temperature sensors, solar temperature sensors, cabin temperature sensors, driver input via the control panel, sensors within the refrigerant cooling system, and even returned signal from directing components within the system. For instance, if the outside temperature is 60 degrees fahrenheit, but the driver asks for 70 degrees fahrenheit, the control module will not automatically turn on the heater, but it will look at the cabin air temperature. If the cabin air temperature is above 70 degrees, the air conditioner or vent air will become active. This is only one operation, but it is a good example of the network of electronic components are at work to comfort vehicle passengers.
What are the symptoms of a bad HVAC Electronic Control Module?
When the electronic control module for the HVAC system fails, the result could be simple or complete failure. Since, as discussed, there is a broad range of components that play a role in the HVAC electronic control system, there are many ways for the HVAC control module to fail. Let's look at a simple, but confusing case. The driver turns the heater on, but, instead, the vents blow outside air and the air conditioner is activated. This could be an internal fault of the HVAC control module causing the control module to misinterpret an air temperature sensor. In this case, that is causing the control module to blow cold air from outside into the vehicle when the vehicle is already cold. This is just one example of what can go wrong, but it is best to understand that erratic or failed operation is most common.
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Can I drive with a bad HVAC Electronic Control Module?
When the HVAC system is behaving erratically or not at all, the vehicle can be driven indefinitely, but the comfort and, depending on the climate, safety of passengers should be considered. In extremely hot climates such as deserts, not having an air conditioner in the vehicle could be considered a risk factor for children and seniors.
How often do HVAC Electronic Control Modules need replacement?
This is not particularly common, but it does occur. Electronic components fail at random, but some things can lead to early failure. Jump starting a battery backwards or improperly can lead to the early failure of many electronic components, especially control modules. Also, spilling liquids on the HVAC controls in the cabin may lead to damage to the HVAC control module, which is often a part the unit housing the controls. In most cases, the HVAC electronic control module should last the lifetime of the vehicle.
How are HVAC Electronic Control Module issues diagnosed?
When the heater or air conditioner, and sometimes other components that happen to be tied into the control module, act erratically or not at all, the technician will go for the diagnostic scan tool. This will allow the technician to view current system operation as long as the control module is still functioning. If during the course of diagnostics any circuit is reading differently in the control module than is input, or the control module is sending incorrect information, it will be considered faulty. This is because all control modules are designed to send information, receive information, and interpret that information based on pre-set information.
How are HVAC Electronic Control Modules replaced?
Like any other control module, the location of the HVAC electronic control module will be identified, and the technician will then begin removing all obstructing components needed to access and remove the control module. Once accessed and removed, the connectors are cleaned and inspected, and the new module will be installed. After all components are reassembled on the vehicle, the technician will program the control module, if needed, and test the operation of the system to ensure the customer complaint has been corrected.
RepairPal Recommendations for HVAC Electronic Control Module issues
When dealing with electronic systems, especially if the issue pertains to the control module, we recommend thorough diagnostics before replacing parts. In effort to correct an electronic failure, it would be very easy to spend hundreds of dollars replacing components before realizing the issue is more advanced. In the case of electronic failures, diagnostics is a must.
What to look out for when dealing with HVAC Electronic Control Module issues
Every possible scenario related to the failure of the HVAC electronic control module can be replicated by one or more failures within the HVAC control system. This means that the control module may be blamed for an external issue, or an external component may be blamed for an internal HVAC electronic control module issue. When the issue has been routed to one circuit, the entire circuit should be tested to prove the diagnosis.
Can I replace the HVAC Electronic Control Module myself?
Except for the very advanced DIY mechanic with a strong understanding of computerized circuit diagnostics and testing, this repair should be left to a professional. Again, diagnostics of electronic systems are difficult for the untrained person to perform correctly. Unless safety and diagnostic methods are understood and followed properly, this should be left to a professional.
Lexus HVAC Electronic Control Module Replacement Cost Estimates
The average cost for a HVAC Electronic Control Module Replacement is between $1,457 and $1,502 but can vary from car to car.