Category: A/C compressor control

ac temperature out of the vents

How the a/c should be operating in order to cool down the interior of your car

Check inside the vehicle:

  • The A/C climate control should be set to Max Cold Position.
  • A/C Climate control set button On.
  • Recirculation/fresh air mode set to recirculate.
  • Engine temperature should be in the normal range (not overheating)
  • Outside ambient temperature should be sensing outside actual ambient temperature.(Ambient temperature should be above 37 F )
  • Engine RPM’s should in the normal everyday range.
  • With the A/C  blower on Max, the mass of air coming out from the vents should be strong.
  • Cabin air Filter should be clean.
  • A/C evaporator coil should be free from debris and leaks.

Check the engine compartment :

  • The front of the vehicle should be free from any road debris.
  • The radiator and A/C condenser should be free from leaves, bugs or dirt.
  • With the A/C system ON the radiator/condenser fan assembly should be operating.
  • The Drive belt should be running all the accessories and in good condition.
  • The A/C compressor CLUTCH should be engaged with A/C ON.
  • The A/C compressor ECV should be modulating the hvac compressor output for max cold.
  • All A/C lines and hoses should be free from dye, oil ,ice or damage.
  • The A/C system should be properly charged with exact amount of refrigerant specified by the manufacturer.
  • Hvac box drain tube should be draining water from underneath the vehicle.



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automotive ac compressor and refrigerant lines

Sun Load or Ambient Light Sensor

The sun load sensor function as an input for the module in charge of automatically controlling the headlight operation and air conditioning system control module.

How to test the Sun Load or Ambient Light Sensor ?

A bright LED light may be used to artificially force the sensor  to adjust for light intensity and angle. With the headlights in the automatic setting position, we should see the running lights coming on and off and the automatic climate control adjusting the air temperature out of the vents. Exposing the sensor photocell to the strong led light will increase the current flow from the sun load sensor while  covering the sensor photocell will decrease the current flow signal to the hvac control module and headlight control module. With a scan tool connected to the vehicle or a multimeter we should be able to see these variations in voltage when the sensor is operating properly. The most common voltage range is between zero and five volts, but is always a good idea to compare the readings against manufacturer specs.

Do you need Assistance with your Sun Load Sensor ?

Contact Us !

automotive ac compressor and refrigerant lines

Solar Sensor, Sun load sensor or Ambient light sensor.

The solar, sun load sensor, or ambient light sensor detects the heat load of the sun, elevation and azimuth. It is used to adjust the amount and direction of the cooled air through the dash vents and to control headlights operation of the vehicle.

Do you need assistance with the sun load sensor in your car ?

Contact us !

Auto AC system service

What is a clutch relay?

A relay is a device that allows you to control high amperage circuit from low amperage circuit.

Automotive switches and electronics are wired to relays since they arent designed to handle the arcing and high current demand required in some circuits.

How a relay works

Every relay has at least two circuits running through it: a low-amperage, or CONTROL circuit, and a high amperage, or load circuit.

When you energize a relay, youre actually energizing the control circuit. This energizes an electromagnet in the relay, which opens or closes a set of contacts. The contacts are part of the load circuit. When the contacts close, they complete the high amperage circuit, allowing current to flow.

Different types of relays

Relays can be normally-open (NO), normally-closed (NC) or can have dual contacts.

Normally-open contact relays have one set of contacts that remain open when the relay control circuit is de-energized. When you energize the relay, the contacts close, completing the high amperage circuit.

Normally-closed contact relays work the opposite way: The contacts are closed when the relay is de-energized. Energizing the control circuit in the relay opens the contacts, shutting off the current in the load circuit.

Dual-contact relays have one set of normally-open contacts, and one set of normally-closed contacts. When the relay is de-energized, current flows through the normally-closed contacts. When you energize the relay, the normally-closed contacts open, and the normally-open contacts close. Now current flows through the normal-open contacts.


Most mini-relays have four or five terminals. The two small terminals(often specified as 85 and 86) are used to energize the coil that creates the magnetic attraction necessary to cause a connection between the high amperage switch contacts.Two other terminals make the high amperage-amperage power in (terminal 30) and power out (terminal 87) connection. Sometimes a fifth terminal (marked 87a) is used as a normally closed (NC) contact, as opposed to 87 being normally-open (NO), which closes when the relay energizes.

Solid state relays

Some manufacturers use solid-state relays in different areas of the car. The operation of these devices is much like an electronic fuel injector. These components can be totally off or tally on, like regular relays. What differentiates them is their ability to be turned on to a certain percentage with a pulse-width modulated signal. The advantage of these devices is that they can control the current flow to the output device, resulting in a variable speed device.

A scan tool is necessary to troubleshoot these solid-state relays. The scan tool can retrieve trouble codes as well as perform output tests on these circuits during the troubleshooting process.

How do I know if my AC clutch relay is bad?

When testing these relays:

  1. Unplug the relay
  2. Measure for continuity between pins 30 and 87a.There should be less than 1ohm resistance.
  3. Measure for continuity between pins 30 and 87.There shouldnt be any continuity between these terminals
  4. Apply power (12volts) to pin 86 and ground to pin 85.The relay should click.
  5. Measure for continuity between pins 30 and 87a.There shouldnt be any continuity between these terminals.
  6. Measure for continuity between pins 30 and 87.There should be less than 1ohm resistance between these terminals.
What are the symptoms of a bad relay?

Signs of a Bad or Failing AC Compressor Relay

The AC compressor will not have power and the AC system will not function.

AC compressor intermittent operation causing weakened or intermittent cooling performance.

If you are experiencing issues with your AC system and suspect that your AC relay has either failed or is beginning to fail, we recommend having it diagnosed by a professional technician.

Auto ac compressor clutch assembly.Air conditioning compressor bearing

The compressor clutch will not disengage when the A/C control is switched to off.

A/C clutch coil shorted.

If the positive wire to the compressor clutch coil is shorted to a 12-volt source, the compressor clutch will not disengage. This is simply because there is no control of the power to the clutch.