Auto Air Conditioning Repair

A refrigerator in a weird layout

Realize that AC in a car is basically a refrigerator in a weird layout. It’s designed to move heat from one place (the inside of your car) to some other place (the outdoors). While a complete discussion of every specific model and component is well outside the scope of this article, this should give you a start on figuring out what the problem might be and either fixing it yourself or talking intelligently to someone you can pay to fix it.

Car air conditioning

Major components to auto air conditioning

Become familiar with the five major components to auto air conditioning:



The compressor compresses the refrigerant in the system (on modern cars, usually a substance called r-134a).



The refrigerant carries the heat.



The condenser receives hot when the compressed refrigerant goes through it.

Expansion valve

Expansion valve

The expansion valve isn’t really a valve and is more like a nozzle.



The dryer/evaporator which adds heat to the refrigerant, cooling your car

Understand the air conditioning process

The compressor puts the refrigerant under pressure and sends it to the condensing coils. In your car, these coils are generally in front of the radiator.

When compressing a gas

  • When compressing gas, the gas gets quite hot.
  • When it is very hot outside, the outside air is cooler and heat can leave the gas.
  • When the pressurized gas has cools, it condenses into a liquid. This phase change makes it hotter.
  • The refrigerant now loses huge amounts of heat.
  • The liquid is then sent to the evaporator, the coils inside of your car. It is still a bit hot, but it is a liquid under pressure.
  • There it goes through the expansion valve, finds a low pressure and evaporates.
  • Evaporation requires a lot of heat energy, so the vapor gets cold. It is this phase change from liquid to gas that really causes the temperature to change.
  • This cold gas vapor chills the evaporator, and your car’s blower blows air through the cold evaporator and into the interior.
  • The refrigerant goes back through the cycle again and again.

4. Check to see if all the R-134a leaks out (meaning there’s nothing in the loop to carry away heat). Leaks are easy to spot but not easy to fix without pulling things apart. Most auto-supply stores carry a fluorescent dye that can be added to the system to check for leaks, and it will have instructions for use on the can. If there’s a bad enough leak, the system will have no pressure in it at all. Find one of the valve-stem-looking things and poke a pen in there to try to valve off pressure, and if there IS none, that’s the problem.

Troubleshooting auto air conditioning

Is the compressor turning?

Make sure the compressor is turning. Start the car, turn on the AC and look under the hood. The AC compressor is generally a pump-like thing off to one side with large rubber and steel hoses going to it. It will not have a filler cap on it, but will often have one or two things that look like the valve stems on a bike tire. The pulley on the front of the compressor exists as an outer pulley and an inner hub which turns when an electric clutch is engaged. If the AC is on and the blower is on, but the center of the pulley is not turning, then the compressor’s clutch is not engaging. This could be a bad fuse, a wiring problem, a broken AC switch in your dash, or the system could be low on refrigerant (most systems have a low-pressure safety cutout that will disable the compressor if there isn’t enough refrigerant in the system).

Look for other things that can go wrong: bad switches, bad fuses, broken wires, broken fan belt (preventing the pump from turning), or seal failure inside the compressor.

Need refrigerant?

Feel for any cooling at all. If the system cools, but not much, it could just be low pressure, and you can top up the refrigerant. Most auto-supply stores will have a kit to refill a system, and it will come with instructions. Do not overfill!

Bad wiring

If you suspect bad wiring, most compressors have a wire leading to the electric clutch. Find the connector in the middle of that wire, and unplug it. Take a length of wire and run it from the compressor’s wire to the plus (+) side of your battery. If you hear a loud clack, the electric clutch is fine and you should check the car’s wiring and fuses. If you get nothing, the electric clutch is bad and the compressor will have to be replaced. Ideally, if you can do this test while the car is running, you can see if the hub spins. That would rule out a clutch that actuates properly but then slips so badly it won’t generate pressure.

Remove air from system

If your system is empty and you’re refilling it, and have access to a small vacuum pump (like what they’d use in a lab or shop), it’s best to suck all the air out of the system before filling it. Air contains moisture, and moisture is bad in ac systems because it corrodes things.

Your system will have a light oil in it. If you vent off any refrigerant, be prepared to wipe some oil off things nearby.

Another possible replacement refrigerant is HC12A which is used quite a bit more in Europe. It performs better than R-134a or R12. It is more flammable. HC12A is more eco friendly than R12 or R134a. Venting HC12A is not believed to cause environmental damage and must be ordered on the internet as local shops do not seem to stock it.

A major issue with HC12A is that shops will not work on a car that has other refrigerants in it. Special equipment is needed for each type of refrigerant’s recovery. For this reason standard R12 or R134a is a safer choice.


  • Be extremely cautious about converting your old R-12 system to R-134a: The R-134a conversion kits sold at auto parts stores and even walmart, are called “black death kits” by some ac repairmen. Frequently, the new R-134a refrigerant will not circulate the R-12 oil and you will burn up your compressor. The R-12 mineral oil has chlorine contaminants that will destroy the R-134a pag or poe special oil. The only way to reliably convert from R-12 to R-134a is to remove the compressor and flush out all the old oil with the new type of oil; then replace the old receiver-dryer or accumulator with a new one; then flush out all the lines, the evaporator, and the condensor with special cleaner then vacuum to a steady vacuum; and finally charge with 70-80%, (by weight) of the original R-12 weight, with R-134a; and expect poorer cooling ability. It is much easier to keep the old R-12 system running with R-12 that is readily availabe via ebay.
  • Illegal: Venting refrigerant — even R-134a — is illegal in the united states, so act accordingly.
  • High Pressure: Never connect refrigerant cans, oil or leak-detector cans to the “high pressure side” of the system. This is often marked with H or High, or a red connector cap. Cans can explode, and that would hurt.
  • Avoid Contact: Stay away from major leaks of refrigerant. As it vents it will get cold enough to freeze your skin.
  • Moving Parts: Look out for moving fan blades and fan belts!
  • Explosive: HC12 is a hydrocarbon, usually some mix of butane or propane. It will explode with an ignition source. Light up a cigarette if you have an evaporator leak and your car becomes a bomb. Professionals don’t use it because of this very reason.

Stay Cool with Air Conditioning Services at P.B. Foreign and Domestic Car Repair

Just like your vehicle’s engine needs a tune-up, your air conditioning system requires regular maintenance for optimal performance. An inefficient AC system can reduce your comfort, especially during the hot Californian summers, and can affect your fuel efficiency. Consult with our expert Car Care technicians to find out when your vehicle’s AC system needs a check-up.

Comprehensive AC Services

We offer a full range of air conditioning services, from basic inspections to comprehensive repairs, to ensure your system is running efficiently. Our services include:

  • AC System Check: We assess the overall health of your AC system.
  • Refrigerant Top-Up: Ensuring optimal cooling performance.
  • Filter Replacement: For cleaner, healthier air inside your car.
  • Leak Detection and Repair: To prevent refrigerant loss and efficiency drop.
  • AC System Cleaning: For optimal air quality and flow.
  • Electrical Checks: To make sure all AC components are working correctly.

Contact Us for Air Conditioning Service

Keeping your air conditioning system in top shape will not only enhance your driving comfort but also improve fuel efficiency and extend the lifespan of the AC system itself. Trust the expertise of P.B. Foreign and Domestic Car Repair to keep your car cool and comfortable. If you need your AC serviced, schedule an appointment or give us a call at 1-858-270-1142.

Need auto repair or car maintenance? Are you in Pacific Beach? Schedule an appointment for a free inspection.

Auto Repair Services

Types of Vehicles We Repair

Servicing a wide range of vehicle types.

Models of Vehicles We Repair

Expertise in various vehicle models.

Jack Kreile
Jack Kreile
August 8, 2023

I’ve been bringing various cars to PB Foreign & Domestic for over 30 yrs. Once agsin, on Monday they provided the best car & customer service I have come to expect from this shop.

I highly recommend them for all your car service needs.

’85 Honda Accord
’97 Nissan Altima
’03 350z
’03 Lexus ES 300
’15 Hyundai Genesis

Diane Greene
Diane Greene
July 29, 2023

Dan, the mechanic is very skilled and honest. I highly recommend asking for him.

ira farnham
ira farnham
June 6, 2023

Great family owned business, run a cool father and son duo. I’ve been taking my cars here for over a decade.

I’ve come across 2 types of mechanics over the years: 1) fixes what needs fixing, checks everthing else out, tells the customer what to keep an eye on/expect in the future. 2) fixes what needs fixing and EVERYTHING else that it touches.

PB Foreign and Domestic is type 1) – straightforward, steady, and honest – which is why I keep coming back and I suspect it’s why the same guys have been working there for forever too.

Aran Osborne
Aran Osborne
April 9, 2023

Best service, best price, they do a great job and are honest! Family owned and operated. I will continue to take my car here. For regular oil changes and maintanance, George is awesome and everyone he employs, this place is great no complaints! Always will look at something if you have a concern like I did. Minor and didn’t Rip me off like most places would have.

Linda Gould
Linda Gould
February 19, 2023

I truly feel like I’m getting the service that’s required and not being upsold on things I don’t need. The price is always better than anywhere else I’ve looked and repairs done timely. They always call if the estimate given to me ends up being different, sometimes it’s lower and if it’s higher they clearly explain why and if it’s absolutely necessary or a recommendation. I trust them.

Jonathan Grannick
Jonathan Grannick
November 18, 2022

If you want a local independent family owned car mechanic that is honest, trustworthy, reasonably priced, and not trying to nickel & dime you these are your guys! Aaron is especially a pleasure to deal with. He went above and beyond at my last oil change to help me on a few things that would have taken tons of time to figure out on my own, you can tell he enjoys helping people (when they aren’t too busy) and is just a personable good natured guy which is so great to have in a car mechanic. Couldn’t recommend them enough!

T. C.
T. C.
May 3, 2022

We really love PB Foreign and Domestic! They have served us well for years on 3 vehicles and have never been disappointed. Highly recommend over dealership or other local facilities. They don’t try to upsell you on things you do not need. Super friendly and can usually get you in within a day or two. It is best to call ahead and make an appointment.

Mandy Anderson
Mandy Anderson
August 25, 2018

Porsche Cayman – my car was overheating so I had my car towed to PB Foreign and Domestic Car Repair. The team was able to repair my car ( I needed a new radiator and water pump) and they gave me very fair pricing. I will definitely come back for my preventitive maintenance.

Need auto repair or car maintenance? Are you in Pacific Beach? Schedule an appointment for a free inspection.