Restrictions
A restriction is a condition where some piece of debris has lodged in a component, and is 'restricting' the flow of refrigerant. Condenser restrictions are the most common. Most late-model condensers have very small passages, as low as 6mms! When there is a restriction in the system, the flow of refrigerant is greatly slowed, or sometimes stopped completely. The blockage causes pressure to build up behind the restriction, and will cause damage to the components behind it.
The most effective way to locate a restriction is with temperature testing. With a good thermometer, temperature (which is pressure!) can be measured ANYWHERE on the system. Large drops in temperature can be identified and repaired. For example, a restricted condenser...If the inlet measures 160 degrees (about 295 psi) and the outlet measures 90 degrees (about 103 psi), it means the refrigerant is slowly leaking past a restriction. Because the refrigerant spends more time in the condenser, it has time to cool of more. Problem is, that 295 psi will continue to build back, and will eventually blow a seal somewhere, probably in the compressor.
Some restrictions can be repaired by flushing the restricted component, but parallel-flow condensers usually need to be replaced.

Improper Refrigerant Charge
As A/C systems become smaller and smaller, the amount of refrigerant in the system becomes critical. The correct charge for an A/C system has been calculated and engineered by vehicle manufacturers for optimum performance. Here are some tips to keep in mind when charging a system:
Charging with cans: A 12 ounce can of refrigerant gives you 12 ounces of refrigerant, right? Well, not always. If you are using a gauge set to charge, those hoses can hold up to 4 ounces of refrigerant themselves. On a 56 ounce capacity system, those 4 ounces might not make a big difference, but on a 1 pound system, you can bet it will. Also, notice how when you pull the can tap off, how the can wasn't quite empty? Yep, another ounce or 2 there.
Too much! Your A/C isn't quite cooling, so you run down to the parts store or a big box retail store, and buy a recharge kit. We in the industry call 'em suicide kits. You add a can of refrigerant. Well, with A/C, too much isn't better.
Retrofitting: Vehicles manufactured prior to 1993 and some 1994 originally came with R12 refrigerant. Because of the cost of that refrigerant, most folks opt to retrofit to R134a refrigerant. Problem is, there is no set standard for how much R134a refrigerant to use in an R12 system. There are many misconceptions about how much to use, and some people have come up with percentages of original charge. I've heard to use as little as 60% of the original charge!
So how do I know if I have the proper charge? Our old friend temperature testing can help determine if you have the proper charge. Orifice tube systems are the easiest and most accurately confirmed systems. It can be done on expansion valve systems, but you'll need to get on the evaporator side of the expansion valve.
Here's how: Measure the evaporator inlet pipe and record your temperature. Now measure the outlet pipe of the evaporator. Those 2 temperatures should be as close to equal as possible, at least within 5 degrees of each other. If the outlet is MORE than 5 degrees warmer than the inlet, you still need more refrigerant. If the outlet is MORE than 5 degrees cooler than the inlet, you have too much refrigerant in there.
Final tip: If your A/C is working, don't mess with. If you have an R12 system, you do NOT need to have it converted to R134a just because someone tells you that R12 is gone. If it's working, leave it alone.
If your system is working and sealed, you DO NOT need to replace your filter drier or accumulator. This is not a part that wears out. The only time you need to replace it is when the system is opened, or if you've had a leak that allows air (and moisture) into the system. If someone tells you you need to replace it every 3, 5 or 7 years, they're trying to sell you something.

We'll be adding more guides and tech tips in the future, so keep an eye out. If you have other questions in the meantime, you are always welcome to visit www.techchoiceparts.com , click on the Sales Chat button, and we'll be glad to talk A/C. Thanks!

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