Category: A/C system diagnosis test

motor vehicle repair near me

Blower motor only start working after i hit a bump.

In most cases that is a sign of worn down blower motor brushes not making a good contact. In some cases the blower motor/resistor pigtail could cause erratic operation of the blower motor too.

What is a blower motor?

The blower motor is a simple squirrel cage type of fan, DC electrical motor. It is located underneath the dash, usually inside the hvac case. Depending on the vehicle, there could be more than one blower motor

What is the function of the blower motor?

Ram air flowing through the evaporator does not provide enough air flow inside the vehicle for cooling purposes so the blower motor forces air past the evaporator and the heater core and out of the vents.

What are the main causes of a blower motor failure?

Noise from the blower motor due to a bad bearing or debris in the fan. A restriction in the cabin air filter that causes internal failure of the blower electrical parts and poor grounds are the main causes of failure and replacement of this air conditioning component.

Sight glass

Auto A/C Sight Glass diagnosis.


A sight glass is a transparent glass tube or window installed in a tank or boiler system that allows an observer to view what is happening inside the system.

The refrigerant sight glass is normally located anywhere liquid flow exists and anywhere it can serve a purpose. When it is installed just prior to the expansion device, the technician can be assured that a solid column of liquid is reaching the device. When it is installed at the condensing unit, it can help with troubleshooting.

Sight glasses come in two basic styles: plain and with a moisture indicator. The plain sight glass is used to observe the refrigerant as it moves along the line. The sight glass with a moisture indicator can tell what the moisture content is in the system. It has a small element in it that changes color when moisture is present.

What you see in the sight glass can help you diagnose system malfunctions. It is strongly suggested that you do not use the sight glass as the only means of diagnosis. Also, do not use the sight glass to diagnose R134a systems.

If the sight glass is clear, one of three conditions can exist: the system is completely empty, the system is full, or the system is overcharged. If there is foam, the charge is low, but if there are only a couple of bubbles, it is probably Ok. few bubbles when the compressor cycles on is normal. Oil streaks in the sight glass usually indicate a low charge and that the compressor is pumping oil from its sump. If the sight glass is cloudy, the desiccant bag has probably burst.

If an R134a system has a sight glass, do not use it or try to perform diagnosis, as it is normal to observe bubbles in this type of system.



System Ok

System overcharged

System empties (No refrigerant)


System low on refrigerant

System contaminated with air


System may be low on refrigerant

Oil may streak as oil circulates


Desiccant breakdown 

Contaminated system



2019 – Renault ARKANA

A car makes a hissing noise each time the A/C system and engine are turned off.

A refrigerant leak doesn’t typically make a noise, except when the refrigerant blow out of the leak. This noise would happen suddenly and would not have a hissing sound. 

Refrigerant leak noise.

On most systems, when the engine is turned off after the A/C system has been on ,a hissing sound will be heard as the pressure within the system equalizes. This is a normal noise. A refrigerant leak doesn’t typically make a noise, except when the refrigerant blows out of the leak. This noise would happen suddenly and would not have a hissing sound.

Air conditioning metering device.Thermal expansion valve

What is the function of expansion valve’s capillary tube in air conditioning?

The capillary tube controls the amount the expansion valve is open. As the temperature of the outlet of the evaporator increases, the expansion valve opens to allow for more refrigerant flow.

The temperature is sensed by a remote thermal bulb attached to the capillary tube of the valve. A decrease in outlet temperature will cause the valve to close, thereby restricting the flow of refrigerant.

How do you test a expansion valve?

A quick test of the expansion valve involves warming and cooling the thermal bulb and watching the change in pressures on the manifold gauge set.

air conditioning service near me

The air-conditioning system cools satisfactorily during the early morning or late evening, but does not cool during the hot part of the day.

The problem is that the A/C system seems to work fine in the early morning and evenings, but does not during the heat of the day. During a performance test, the low-side gauge reads normal and then drops dramatically.

  • Ice could be forming on the expansion valve
  • The receiver drier could be saturated with moisture

Moisture in the system can be released from the desiccant in the receiver-drier by an increase in temperature on the high side. When the ambient temperature is lower the desiccant may be able to hold the moisture out of the refrigerant. Internal freezing of the expansion valve could produce external icing on the valve.