Sunday, January 27, 2008

What is Vacuuming the A/C system, and why do I need to do it?

When you vacuum an A/C system, you're not cleaning it, you are removing AIR and MOISTURE. A vacuum pump is connected to the yellow hose of a manifold gauge set. The pump pulls all of the air out of the system. Also, water 'boils' in a vacuum, so all the moisture is removed from the system. Air and moisture are harmful to an A/C system, because they react with refrigerant, and create an acid that can damage or destroy seals and o-rings.

A vacuum is pulled AFTER all the components have been replaced and the system is sealed up, but BEFORE refrigerant is added. Typically, the vacuum pump should be left running for about 1 hour, longer in especially humid climates, or when the A/C system has been left open to air for an extended amount of time. A vacuum must be pulled anytime the system has been exposed to air, or had a toal loss of refrigerant.

Most vacuum pumps will only pull a vacuum of 28 psi max. 26-28 psi is fine. I normally let the vacuum run for about 15 minutes, then I shut the valves on the gauges and watch for a minute or so. If the needle on the low (blue) side starts creeping back towards zero, I know something is not correctly sealed. If it holds solid, I will re-open the valves and let the pump run.

While vacuum pumps are pretty expensive, many retail parts stores rent or loan them to the do-it-yourselfer. There are less expensive, but less efficient models that run off of shop air, and those will work fine for the ocassional odd repair.

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Wednesday, January 23, 2008

General Motors Compressors - Locked Up Out of the Box

You just bought a brand new, or remanufactured, General Motors type compressor (HR6, HT6, R4), and it's locked up staight out of the box! ...Or is it?

GM compressors have Teflon piston rings on the end of each piston. R4 Radial compressors have 4 pistons, and 4 Teflon rings. HR compressors have 3 pistons, with a Teflon ring on both ends, so 6 Teflon rings total.

These piston rings are pressed onto the end of the pistons with a die, then quickly installed in the compressor cylinders during assembly. Quickly, because these rings expand or 'flex', trying to return to their original shape.

Once installed in the compressor cylinders, these Teflon piston rings will expand, and form a kind of positive seal. While very tight, the compressor is not locked up.

Another way to think of it is with a jar or, say grape jelly. While very tight, the lid is not locked onto the jar. You just need some assistance to open it the first time, maybe a rag or your shirt tail. Once opened, the lid is forever easy to remove.

The same goes for your new General Motors A/C compressor. With the use of a tool called a 'spanner wrench', available for sale or rent at most auto parts stores, you'll have the extra leverage to get that compressor rotating in no time.

Monday, January 21, 2008

Why do I need A/C in the Winter?

The quick answer is this: defrost.

To explain further, the A/C system doesn't just cool the air, it 'conditions' it. Whether you want cold or warm conditions is your choice. The A/C system is also a dehumidifier, removing moisture from the air. Most defrosters run with the A/C system these days.

Also, because most engines have a single serpetine belt driving all the accessories, a locked up compressor can cause further problems, including a broken drive belt, resulting in a stranded motorist.

If you are not going to replace your locked up compressor, do not turn on your A/C or defrost.