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My son, who lives in another state, called me up one day to ask how to get a stripped lug nut off. He was replacing the rear brakes on his old Ford Ranger and couldn’t get the wheel off because one nut was rounded off. He had spent hours and tried everything, but since the nut was recessed deep into the wheel, he was limited to what he could do. I told him to look in the hole with a light to see if any flats were left on the nut. He said there weren’t. We discussed various possible solutions, and he unsuccessfully tried them all. Finally, I suggested that an impact wrench with an extractor socket might work, so he went out and bought a wrench, a compressor, an air hose, and a set of impact sockets.

I didn’t hear back from him that day, so I called him the following day to find out if he got the wheel off. He did succeed in doing so, but only after discovering that it was a locking lug nut, and the key was in the glove box!

Dan in Arizona

Typical Locking Lug Nut & Key

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Tesla's maintenance page says, "We recommend replacing your A/C desiccant bag every 2 years for Model S vehicles produced in 2012-2020..." The owners manuals for many late-model GM vehicles (Corvette, Malibu...) recommend replacing the A/C desiccant bag every 7 years. Other brand vehicles (Chrysler, Ford, Hyundai...) also have A/C desiccant bags but may not have any, or at least any easy to find, recommended replacement intervals.

Here is how refrigerant typically flows through an automotive A/C system:

1. Compressor pressurizes (and heats) refrigerant gas
2. Pressurized refrigerant cools from gas to liquid in the condenser (typically located in front of the engine's radiator)
3. During the trip from the condenser to the evaporator, a fixed orifice tube inserted in the refrigerant hose or an adjustable expansion valve reduce pressure to cool the refrigerant and allow it to turn back into a gas inside the evaporator (located in the vehicle's interior)
4. Low pressure refrigerant gas flows back to the compressor

Absorption of harmful moisture and metering of refrigerant flow/pressure/temperature differ depending on if the system uses an orifice tube or an expansion valve.

Orifice tube systems have another part called an accumulator between the evaporator and compressor. The accumulator canister gives the refrigerant more time and space to completely turn from liquid to gas before entering the compressor. Desiccant in the accumulator absorbs moisture.

Expansion valve systems do not have an accumulator (the expansion valve itself controls flow/pressure/temperature). To absorb moisture, there is either a receiver drier canister or a replaceable desiccant bag (a.k.a. "A/C Receiver Drier Desiccant Element") between the condenser and evaporator. A replaceable desiccant bag will typically be inside a tube mounted on the side of the condenser.

Automotive A/C maintenance used to tend towards, "if it ain't broken then don't fix it." If A/C repairs and/or refrigerant recharging is necessary then the accumulator or the receiver drier is also replaced to get rid of any moisture and contaminants that have accumulated in those parts. A replaceable desiccant bag (often accompanied by a small filter element) instead of a receiver drier now makes it more practical to do preventative maintenance. Typically a plug is unscrewed to access the desiccant bag (and often a filter element). The refrigerant must also be extracted and replaced (requiring specialized tools), but the system will now have freshened refrigerant, oil and desiccant which hopefully will extend the life of more expensive A/C system parts like the compressor.

GM's 7 year replacement interval seems reasonable. Desiccant bags might be saturated and filters might be grimy after 7 years. On the other hand, Tesla's 2 year desiccant bag replacement interval for the Model S is quite short. I have not heard or read anything about new refrigerants (R1234yf) being more likely to attract moisture. A clue might be that for the Model 3, Tesla's maintenance page says the replacement interval is two years longer "if it doesn’t have a heat pump." Tesla may have conservative maintenance intervals to better protect the remarkable (and expensive) heat pump system which provides A/C and heat for both the vehicle interior and propulsion batteries.

See the components that make up your specific vehicle's A/C system under "Heat & Air Conditioning" in the RockAuto.com catalog. The "A/C Compressor & Component Kit" section offers quick examples of all the parts that should be replaced to better eliminate moisture and other contaminants from the system (including shards from a failed compressor...).

Tom Taylor,
RockAuto.com

To read more of Tom's articles, click this link and choose from story titles on the Newsletter Archives page.