Auto Q & A - Your Auto's Heating and Cooling

Q. My A/C was recharged several weeks ago and ran well until one afternoon, when it was only blowing warm air. It blows warm air even when it is cool outside. I need to know what it could be before going to the mechanic.

A. By far, the most common cause would be a slow leak in the system, and Freon might have been lost, causing warm air to blow. There also can be lots of other possibilities. Try going back to the shop where the care was done or a different one to see what they find. Air conditioning work requires lots of equipment and is not really a do-it-yourself repair.

Simply recharging an A/C system never fixes anything. An electrical problem may have occurred if there is a leak. The system has three major components and a few smaller ones. Most of the time, your problem lies in at least one of the three big ones: compressor, evaporator, and condenser. It also has a small metal can, containing desiccant, which should be changed whenever the system is opened. The components are in different locations in the car, so there really is no such thing as replacing the whole air conditioner as many people think they have after a major repair.

Depending on the vehicle, there are several feet of hard and flexible lines that can become damaged can cause a leak. The best thing to do now is to have it evacuated and recharged with the addition of dye to aid in finding the leak in the very near future. If you do not wish to go to the dealership, find a reputable A/C specialty shop or independent garage that does full-service A/C work. Finding leaks in A/C systems these days is not hard since there are high-tech leak detection tools. Good A/C shops will even show where the test equipment is detecting the leak. Most shops use either a "sniffer" or a special dye that shows up under backlight.

Q. A gasoline smell is coming through the air conditioning vents. Please help!

A. Could there be a fuel leak under the hood somewhere? Have it checked immediately. Preferably, have it towed if you need a pro to evaluate. THIS IS POTENTIALLY A VERY DANGEROUS SITUATION.

Q. I recently purchased a '95 Toyota Camry DX. When I run the air conditioner, it smells very bad. How can I get rid of the smell?

A. The air conditioning problem is most likely your heater core. It should smell like a stinky syrup or hot antifreeze. If you drive it around at night and the windows fog up real easy, it is your heater core. You could go and have it repaired or bypass it all together if you live someplace hot like Phoenix. It can also be mildew on the evaporator. They make a few chemicals that can be shot in there. A spray of bleach will work, also. The hardest thing is getting access to the core. You may have to cut a one-inch hole in the housing to get a good shot at it. Just make sure you know where you're drilling and stay well clear of the core. A little A/C tape will cover the hole afterwards. Once you kill the smell, you can prevent further mold by turning off the A/C and having the selector set on fresh air, not recirculation, with the blower on high. Let it run for a minute or two. This will dry the evaporator and ducts.

Q. When outside temperature is cold (less than 15°F), the temperature indicator in my dash indicates that the motor doesn't reach the normal operating temperature. This is happening when the car is in movement. On the other hand, if the car doesn't move, the temperature will be reached, but it will drop once I move fast. In addition, when the indicator says the motor isn't hot enough, there's no heat at all that comes from the ventilation. Heat will be back when I let the car run without moving and let the temperature reach normal status. I do not have this problem during summer, when it's not freezing. Before assuming the only component failure is the thermostat, what could be involved here?

A. Your thermostat is more than likely stuck open. By opening and closing, the thermostat helps keep the engine at correct operating temperature. When it goes bad, it will either stick open or closed. If it sticks open, then your engine will be slow to warm up and won't stay at operating temperature. If it were to stick closed, then the car usually overheats because the coolant can't flow to the radiator. On most cars they aren't hard to change or get to.

Q. About three weeks ago, my car wouldn't switch between vent and defrost. I tore it apart to try to find the problem, and in the process, it quit heating (the A/C isn't working either). The blower continues to work fine. The LED's on the A/C and the recirculation work. The rear wiper/defrost on the same control panel works also. I sent the temperature control in to be rebuilt, replaced it, and still nothing works. What I should look at next?

A. There may be a way is a way to reset the climate control head. It involves pressing and holding certain buttons, though I don't remember which ones. Try calling the local car dealer for details; I would think they would tell you. Tell them you are a tech from a local dealer working on a used car.

Q. I have a 1994 Buick Lesabre. The air conditioner is working but when I have it on I hear something clicking on and off repeatedly. The air seems to be working fine - it's cold. When I first turn it on, I can hear the compressor turn on. After it's on a while, it sounds like the compressor turns off, then turns on, turns off, then turns on in rapid succession. I'm puzzled. It also does the same thing when you switch on the defroster. If it was the air conditioner compressor, why would it affect the defroster?

A. The air conditioner is needed for the defroster to work. If you tried to defrost using the same air that was causing the windshield to fog up, you would get nowhere. The air conditioner dries, as well as cools the air. This allows it to absorb the moisture (fog) as it blows over the glass and clears the windshield. The clicking sound is a magnetic clutch, which allows the compressor to run or be turned off. The high or low limit switches usually cause the cycling of the compressor. These temporarily shut off the compressor to prevent damage to it. In your case, I'm guessing low pressure. The only way to really find out the extent of the problem is to take it to an auto air conditioning specialist. Pay for a diagnosis and then decide if cool air and a clear windshield are worth the cost of repairs. Your current problem will only get worse with time.

Your problem is normal on that system and is affected by temperature and demand. If it's running in cooler conditions (outside air temperature), it will cycle more frequently. If you have the blower speed set on low (low demand), then it will cycle more frequently. So, you may not have a problem. The real test is when you get a warm sunny day, the interior is hot and you have it set on MAX and high blow. If it cycles then and the air temperature at the vent is not cold, it's probably low on refrigerant and should be checked by a good A/C tech.

Q. I had no heat in my car this past winter. I flushed the heat coil and that worked. No heat now, again. About a year ago, I found out that the A/C compressor comes on with the defogger when it's above a certain temperature outside. It's in the high 80s outside now. Is there something that prevents the heater from working when it's hot out?

A. The compressor coming on with the defogger is normal, it keeps it from seizing up over the winter. No, there is nothing to keep the heat from coming on in hot weather. Since turning the heater on removes heat from the cooling system, it actually cools the engine. Often heater cores plug up again even after they are flushed. Flush it again; if it goes away great, but it may only be temporary. There are products that claim to help flush cooling systems. It might be worth a shot to try.

Q. My wife told me the car's A/C is not working. I went outside to check and sure enough she was right. I checked to see if the compressor was turned on, and it was. I added some R134a to the system and it started to get cool; I added the required amount, and it started to get cold. There is something green leaking. What can this be?

A. The system is leaking refrigerant. The green stuff you noticed could very well be the UV dye that is sometimes put in the system to help look for leaks.

Q. I have a 2002 Chevy Avalanche. When the engine is at idle speed either at startup or at stop sign, the A/C blows hot air. It works excellent when driving. What is not working?

A. It sounds like either the fan clutch is getting weak and not pulling enough air across the condenser, or the compressor is getting weak. If memory serves correct, it's a variable speed compressor and one of the first signs/symptoms of it going out is not producing enough pressure at idle.

Q. My 1998 Dodge Caravan overheats only when I turn on the A/C with the recycle on. Seems the air conditioner alone will not cause the overheat condition. Can I check the fans while the engine is still cold?

A. If the air conditioner is working OK and still blowing cold air, the fans should be on or cycling on and off. Anytime the A/C is on, even on a cold engine, just start the engine and turn on the A/C and look at the fans. They both should kick on and be running within a few minutes. They can cycle on and off based on air conditioner pressure readings.

Q. My friend has a 1998 Chevy Malibu and her HVAC controls speeds "1" and "2" don't work. I know that this is a common problem with 1997-2002 Chevy Malibus, but don't know what the problem is, what the solution is, and how much it would cost to fix the problem?

A. Aside from the MVAC controls, you should find the same problem in heater mode. Your resister stack is bad. The blower motor resistor is located on the passenger side, under the dash. You need to remove the closeout panel, under the glove box. Look up in there and you will see the blower motor, and just over and off to the left you will see the blower motor resistor. Two or three screws secure the heater box - they are 5.5mm (7/32).

Q. I have a 2002 Mitsubishi Galant. The heater is not pumping out any heat at all. It is cold air only. What could be the problem?

A. You may be low on coolant or have a thermostat stuck open if the engine temperature gauge stays in the cold range. A thermostat is cheap. Check the coolant level first or have it checked at a full service gas station. It could be something else such as a blend door problem.

Q. I recently noticed some white vapors coming from the A/C vents of my '99 RAV4. I would turn the unit off until I can bear the heat no longer. When I turned the A/C back on, everything is fine. This has happened several times in the past two weeks. What was the source of the white vapors and should I be concerned?

A. It's probably water vapor. You are making your own miniature clouds. Check under your RAV after driving for a while with the air on and see if water is dripping underneath. If not, your drain tube is clogged and condensate is accumulating in the heat/air box. If you unclog the tube, the clouds should go away.