It Must Be Low On Freon

 How many times have I heard that?  The air-conditioner is not making things cool like it used to, whether it's the house, the car, the boat or the RV.  Nobody wants to appear as if they don't know anything so they need to say something that shows they are not completely ignorant. Whether it is wishful thinking or they are simply trying to impress the service technician so that he will think he is dealing with a knowledgeable owner and not try to stick them for an unnecessary expensive repair is a good question, but the fact is, low Freon is rarely the culprit when the darn thing just isn't putting out.

   There is one exception thought and that is automobile air-conditioning. Due to the fact that the compressor is mounted on the engine and the engine vibrates a lot the connections to the condenser (the radiator like thing in front of the real radiator), and the evaporator (the cold part hidden under the dash) are made of flexible tubing connected to non-flexible metal fittings. Over time these flexible lines become not so flexible due to heat and age and vibration and the joints leak. This is why you find charging kits in auto parts stores and you don't find them in hardware stores.

   While they all work on the same principle, auto air-conditioners and home refrigerators use one kind of "Freon" and home, boat and RV air-conditioners use a different kind. On older cars and refrigerators, pre 1995, the system used R12 and now uses R134a and the two don't mix, so before you recharge your system with R134a make sure that is what it takes. The connections for R134a are different than for R12 so you won't be able to charge an R12 system with R134a hoses. If you have an R12 system and it leaks you should get it converted to R134a as R12 is no longer available at the auto store and is VERY expensive from a dealer. Getting the conversion will be cheaper in the long run and is more environmentally friendly according to the EPA, so do your part for the environment and save money.

   Now if your system is low on gas then that is not the problem. The problem is you have a leak somewhere in the system and it needs to be found and fixed before you recharge it. Being low on Freon is a symptom of another problem not the problem itself. If it was working one day and not the next or you recharge it and it all leaks out in a week then you have a big hole and it should be easy to find, if it takes three months to leak out you are unlikely to find it without a leak detector.

   On most cars there is a receiver/drier between the condenser and the evaporator and they have a little sight glass window in the top through which you can see the liquid Freon on it's way to the evaporator. After running the air conditioner for a minute or so this window should show only liquid. If you can see any bubbles in the liquid or it seems foamy then you may be low on Freon.

   If you don't see anything at all you may be completely out of gas, in which case you will have not cooling, or it may be completely full and working normally.

   On an automobile, if there is still some gas left in the system, that is if it is working somewhat, with the engine OFF pour a little soapy water over all the joints that you can see, metal to metal and rubber to metal, then watch carefully for bubbles. You might need to wait awhile for one to form if it is a slow leak. On some compressors the connections have O-ring seals and these can leak so pour some there too. There are also dyes and sealers you can buy in auto stores and on eBay for the 134a systems that are fairly inexpensive so you might want to try that. There are fluorescent dyes as well but these require a special light to illuminate them and so the cost is higher. One problem with the dyes that I've found is that if you don't get it in properly it can spray all over everything making it totally useless from then on and if there is a leak it is almost always on the backside of a fitting or somewhere else where you can't see it.

   If you do find the leak this way then try tightening the joint with two wrenches but be careful not to over tighten as some of these lines are aluminum and break easily. If you get a little movement then check with the soapy water again, you might have got it.

   The one place you are not going to find a leak this way is if it is in the evaporator. Because it is hidden behind or under the dashboard you cannot see bubbles or dyes and need an electronic leak detector. If you don't have one then you are going to have to take it to an a/c guy for him to find the leak. You might want to do this anyway because can have more than one leak particularly on an older system and he will know where to look.

   OK, as I said in the beginning, what if it isn't low on Freon?

   The compressor is driven by  belt or belts from the engine and is turned on or off by a magnetic clutch on the front next to the pulley.  When you turn on the air 12 volt power is sent to the clutch and it engages and the compressor turns. You should hear a click and then the front face of the pulley will turn and the hose that goes to the condenser at the front will get hot and the hose coming back from the evaporator will get cool. If this doesn't happen then it may be a 12 volt problem. It could be something simple like the plug-in-electrical connector to the compressor has come loose and reconnecting it solves the problem. I have amazed a couple of people by fixing a "broken" system just by doing that. One of them had had a "broken" a/c for several months and couldn't afford to take it in to a repair shop.

   If that isn't the case it could be the high pressure switch is preventing it from engaging or even a bad fuse but in the case of the latter the blower usually won't work either as they are on the same fuse. Sometimes there is a relay in the system as well and that could be bad but that is hard to check for and I am just covering the easy stuff here.

   A high pressure switch disconnects power to the compressor clutch if the pressure gets too high. This can happen if you have electric fans and they stop working or if the condenser is clogged with bugs or anything else you may have picked up while driving, such as a piece of newspaper or a plastic bag. Of course if any of these have happened you will have a high engine temperature too. You can bypass the high pressure switch just to see if it is faulty. If it is, then the clutch will engage when you turn the a/c on and you need to replace that switch. DO NOT try to fun the system without a working high pressure switch as this can lead to very expensive problems such as blown hoses and compressors.

   On most auto systems there is a freeze sensor on the output from the evaporator going back to the compressor. It is basically a thermostat that senses when it is getting too cold. This can happen when it is cool in the vehicle and the fan is on low speed, or the system is low on Freon. Either way it also cuts power to the a/c clutch and turns off the compressor.  If the switch is bad or if the wires have become disconnected the compressor won't turn on. Always check for disconnected wires if the a/c doesn't work right after you just had some other work performed on the engine such as an oil change or air filter change or new spark plugs.
It is very easy for a mechanic or owner to not notice a loose wire connector when they are struggling with a stubborn bolt or spark plug.

   One last thing that can throw you a curve is if the system has a suction pressure regulator in the evaporator. It is there to keep a constant pressure and temperature in the evaporator and if it stops working, even when everything else seems to be right, you will have poor cooling performance. Not that you usually want to mess with this as it is buried under the dash but if you have to, you have to know it's there.

   Always remember to wear protective gloves and glasses when working with high pressure Freon. A frost bitten finger is one thing, a frozen eyeball is quite another. Save the ice for that cold one you are going to have later to celebrate a job well done!

Brian Ratcliffe
2008
Marine Air Conditioning Service Secrets