On The Road

The art of staying cool

I really appreciate having air conditioning in my car and in my house – especially after the extremely high temperatures in late July.

We work on air-conditioning systems year-round, but the work picks up in the summertime. I have always found air conditioning to be interesting for one fundamental reason: All refrigerant systems follow the same basic principles. From cars to homes to refrigerators, they all work the same basic way. My background in automotive A/C helped me solve a problem in my house.

Air conditioning or refrigerant systems always use low-pressure gas known as Freon. This gas, which typically starts off at approximately 30 pounds per square inch (psi), is pulled into the A/C compressor, a pump that converts Freon into high-pressure gas. Depending on the outside air temperature, the high-side pressure coming out of the compressor could vary from 120 psi to 250 psi and up.

As Freon comes out of the high side, it is also extremely hot and must be cooled. It then flows into the condenser, which is a heat exchanger. The condenser sits in front of the engine’s radiator.

The auxiliary fan sits on the condenser; as soon as you turn on the air-conditioning system, the auxiliary fan turns on. If you have ever walked by an outdoor A/C unit while it is running, you can feel the heat being removed from the condenser by the auxiliary fan. Now that the high-pressure Freon has been cooled, it flows through a filter called a receiver dryer that removes dirt and moisture. It then flows through an expansion valve.

High-pressure Freon flows into the expansion valve, but liquid Freon flows out. The expansion valve regulates the flow of liquid Freon to the evaporator core, which sits inside the dash, inside the heater box. The evaporator core is also a heat exchanger. The dash blower motor sits right next to the evaporator core.

As warm, moist air gets blown across the evaporator, it is cooled and dried. This cool, dry air is what you feel coming through the vents in your car or the vents in your home. Once Freon leaves the evaporator, it is a low-pressure gas – and the entire process starts all over again.

Here are a few common A/C complaints and symptoms we hear from customers: The A/C takes a long time to get cold; the A/C is only blowing cold out of half of the vents; the A/C just does not work that well. These are usually caused by low Freon in the system.

I also often hear complaints of the A/C compressor making a noise or the A/C clutch cycling. These are indicators that the compressor could be going bad.

When a customer tells me his or her car’s A/C system smells like mold, I usually find that the evaporator core is contaminated with bacteria or the cabin filter is extremely dirty. When I learn that a car’s engine runs hotter when the A/C is on, it usually is because the condenser or the auxiliary fan is malfunctioning.

Same principles

My A/C knowledge helped me fix the unit in my house that wasn’t working properly on a hot day last month.

I went out to the A/C unit and made sure the auxiliary fan was cooling the condenser and checked the sight glass to see the Freon level. I felt the high-side and low-side lines to make sure they were the correct temperature. All of those things checked out. So I went to the furnace, which is essentially a heater box, and looked at the evaporator core inside the furnace assembly. I turned the A/C system off to stop the fan from running and checked the furnace/air-conditioner filter. The filter was clogged with dirt, dust and several candy wrappers (I have two little boys).

The furnace filter is the same thing as a car’s cabin filter. I replaced the filter and started that system. Within 30 minutes, the house was 5 degrees cooler.

This may be the last time I compare a car with my house, but with the way technology is headed, I wouldn’t bet on it.

Matt Pataky owns Sunnyvale Foreign Car Service, 15 Pioneer Way, Mountain View. For more information, call 960-6988, email This email address is being protected from spambots. You need JavaScript enabled to view it. or visit sunnyvaleforeigncar.com.

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