VW AC Compressor Solenoid Valve Symptoms—What Are They?

Are you having AC issues with your Volkswagen? Do you suspect that the solenoid valve is the culprit, and want to know if the symptoms of a failing compressor solenoid valve match the signs that you’re having? You’ve come to the right place, for we have researched this question, and we have the answer for you.

Here are the symptoms of a failing compressor solenoid on your Volkswagen.

  1. Inconsistent cooling
  2. Delayed cooling
  3. Unresponsive AC controls
  4. Recharging the refrigerant that doesn’t improve the condition

In the succeeding sections, let’s talk more about each symptom of a failing AC compressor solenoid valve.

Read on!

A Volkswagen Jetta on display at the Chicago Auto Show media, VW AC Compressor Solenoid Valve Symptoms - What Are They?

What is a Variable Displacement Compressor?

Traditional auto AC systems use a compressor clutch to engage and disengage the compressor.

The compressor’s pulley spins with the movement of the serpentine belt and the crankshaft.

The crankshaft is in constant rotation when the engine is running. The crankshaft is responsible for converting the reciprocating movement of the pistons of an engine into rotational motion.

When you turn on the car AC, the compressor’s clutch engages the compressor’s pulley. This causes the rotation of the pulley that provides power to the compressor. When you turn off the car AC, the compressor’s clutch will disengage the pulley.

This type of compressor is the FDC or the Fixed Displacement Compressor.

Modern compressors no longer use a clutch system like the one in a Volkswagen car. Instead, modern compressors, or Variable Displacement Compressors (VDC), can change their pumping capacity depending on the need.

If the cabin temperature is high, the VDC will increase the capacity of its pistons to allow for more refrigerant. Once the cabin temperature becomes routine, the piston’s ability will shift down to match the cabin temperature and cooling load.

Car aircond compressor during maintanace work. selective focus

VDC Compressor Types

There are two types of VDC compressors. The difference between these two types depends on the system that controls the displacement of the cylinders and the system that regulates the cylinder capacity. Thus, most internal structures of these two types are the same.

ICVDC (Internally Controlled Variable Displacement Compressor)

This type of VDC uses the refrigerant pressure at the compressor’s suction chamber through a unique diaphragm.

When the cabin temperature is high, refrigerant is needed to cool the cabin air. The higher demand also increases the low-side pressure. The high pressure moves the diaphragm, pushing the wobble plate to its greatest angle.

A high plate angle will increase the capacity of the pistons to its maximum, displacing the most amount of refrigerant. The angle of the wobble plate drops as the demand for cooling drops because the pressure on the low side will also decrease.

The diaphragm responds to the changes in pressure, pushing or pulling the wobble plate accordingly.

Some ICVDC systems still use a clutch system to engage and disengage the compressor’s pulley if there is no need to use the compressor.

ECVDC (Externally Controlled Variable Displacement Compressor)

Instead of a diaphragm, the ECU (Engine Control Unit) controls the suction and discharge using a solenoid valve.

The ECU (also known as the ECM or Engine Control Module) is responsible for getting data from various sensors inside your Volkswagen vehicle. The ECU can make multiple decisions that affect the performance of your car depending on the data it brings.

Temperature sensors inside your Volkswagen's cabin influence the solenoid valve's behavior.

An ECVDC has better control over the displacement of the piston because it is not dependent on the pressure of the low side of the AC system.

Moreover, since the system has more control in an ECVDC system, there is no need to use a compressor clutch to engage and disengage the compressor’s pulley. The ECU can modify the amount of refrigerant using the solenoid valve.

How does a solenoid valve work?

solenoid valve

Solenoid valves combine a solenoid on top and a valve below. Thus, a solenoid valve will look like a regular valve with electrical wiring from its top part.

The ECU can activate and deactivate the flow of electricity into the solenoid half. When there is no electricity, the solenoid half does not produce any electromagnetic field.

However, when the ECU activates the flow of electrical energy to the solenoid valve, the magnetic field also activates.

The center of the electrical coil inside the solenoid part is an armature. There is a spring and a plunger inside the armature. The plunger seals the valve.

If the system uses a naturally open solenoid valve, a spring pulls the plunger when the electromagnet is off, keeping the valve open. However, if the system has an inherently closed solenoid valve, the spring pushes the plunger into place when the electromagnet is off, closing the valve.

Activating the electromagnet moves the plunger in the opposite direction of its natural position. Thus, the electromagnet will push the plunger to the open position in a naturally closed valve and a closed position in a naturally open valve.

What are the symptoms of a failing solenoid valve?

Electrical solenoid valve used to control the opening

Now that we understand how the solenoid valve works and the type of AC compressor that uses it, it will be simpler to understand the different symptoms of a failing solenoid valve.

Even though the two types of Variable Displacement Compressors have different methods of controlling the performance of the compressor’s pistons, some of the symptoms will be the same across the two types.

However, even though there are similar symptoms, troubleshooting will be different. Some ICVDCs still use a clutch system, which can be a point of failure. ECVDC systems do not have a clutch system.

Additionally, an ECVDC system uses feedback from the ECU and electrical energy to manipulate the position of the valve. A problem with the ECU or the circuit can cause a problem with the ECVDC.

Keep in mind that recharging the refrigerant will not fix the problem. If the problem persists after recharging, one of the symptoms below will confirm that it is a problem with the solenoid valve.

Here are the common symptoms of a failing solenoid valve.

Inconsistent Cooling

Air conditioning in the car blowing strong cold air

Opening the AC of your Volkswagen vehicle on a hot day, you might notice that the AC needs to generate the right amount of cold air. In some situations, the AC might produce too much cold air when you turn it on for moderate cooling.

You might experience situations where there is no cold air coming out of the AC vents.

Contaminants in the refrigerant can create a blockage in the valve. This can lead to an incomplete valve opening (or closing).

Another possible cause is metal shavings inside the compressor that reach the solenoid valve. The metal shavings can get between the valve and the valve wall and limit the movement of the valve.

When the valve doesn’t open or close as much as it needs to, the refrigerant will not be able to get into the compressor at the correct volume. This leads to inconsistent cooling.

A naturally open valve will generate too much cooling, while a system that uses a naturally closed valve will produce minimal cooling. The exact symptom will depend on the type of ECVDC that your Volkswagen AC system operates.

To solve this problem, it is best to replace the compressor.

Replacing the solenoid valve will fix the problem, albeit temporarily. If you don’t replace the compressor, the issues inside the compressor that created the blockage in the solenoid valve can create another blockage. Replacing the compressor will fix the root cause of the problem.

Delay In Cooling

A delay in cooling makes it seem like your AC takes too long to produce cold air. If you experience a lag or delay before your AC starts to cool the air inside the cabin of your Volkswagen vehicle, then it could be a problem with the solenoid valve.

This issue can happen when corrosion takes over the electronic contacts of the solenoid valve. Corrosion on the connections will limit the amount of electrical energy that gets to the solenoid valve, creating an inconsistent energy flow. This can affect the effectivity of the solenoid half to open the valve.

You can fix this issue by spraying the area with a contact cleaner.

You can clean the electrical contacts with a corrosion remover to remove tougher corrosion, then apply some contact cleaner.

Hosa D5S-6 CAIG DeoxIT Contact Cleaner is available on Amazon through this link.

Unresponsive AC System

When the AC system in your Volkswagen becomes unresponsive—it doesn’t cool the cabin no matter how long you wait for it to do so—the problem could be the solenoid valve again.

The spring that keeps the plunger open or closed will eventually wear out. Corrosion can also cause this problem. Corrosion inside the plunger and spring can cause the plunger to seize and stop moving.

If the corrosion is not that bad, you might get away with cleaning the solenoid valve if you can open the solenoid part and get to the plunger and spring.

In most cases, it would be easier to replace the solenoid valve.


A Volkswagen Jetta on display at the Chicago Auto Show media

Even though the solenoid valve gives the compressor more control over the cooling of your Volkswagen vehicle, it can be tricky to troubleshoot without knowing the correct symptoms.

If you found this article interesting, why not check the two articles below?

Does AC Compressor Control Heat In Car?

AC Compressor Bolts Broke Off—What To Do?

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