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I drive a 2010 VW Golf. The AC has not been working at all lately. Before taking it in to the pros, I bought an AC Recharge Kit and only got to step 1 on the directions.

When I hooked it up to the "high" side of the AC compressor, the pressure gauge showed 30 psi. Step 1 is something like "slowly release refrigerant into the system until the pressure reaches 30 psi."

So I concluded that it wasn't in fact low on refrigerant and took it into the dealership. It turns out it was in fact very low on refrigerant.

What did I do wrong? (I know that DIY AC Recharging is not recommended but I've done this multiple times on my previous car without any difficulties.)

I understand that this is probably car-specific so let me know if you need pictures of what exactly I tried.

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4 Answers 4

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You should have been charging on the low side not the high side. But it's actually good that you weren't able to top off the system. You should never use that stuff in any car AC system and it's outlawed in the states. This is a flammable refrigerant!

From the SDS (Saftey Data Sheet)

AUTO – IGNITION TEMPERATURE: 1585 F

FLASHPOINT: -34 C

LOWER FLAMMABLE LIMIT (LEL): 1.9%

UPPER FLAMMABLE LIMIT (UEL): 8.5%

From their directions:

Although RED TEK® 12a is compatible with most existing refrigerants and oils, DO NOT MIX REFRIGERANTS. Mixing refrigerants is illegal in Canada and the US and will not offer the maximum performance available from RED TEK® 12a.

RED TEK® 12a Refrigerant is installed through the LOW SIDE SERVICE PORT AND IS CHARGED AS A LIQUID INTO A "0" ATMOSPHERIC CONDITION. DO NOT INSTALL INTO A SYSTEM WHERE A HARD VACUUM EXISTS. DANGER!! DO NOT INSTALL ON HIGH SIDE SERVICE PORT.

Had you have topped off your system, and then taken it to get it repaired somewhere they would need specialized equipment to recover what would now be a blend because you mixed different types of refrigerant. Most shops just won't work on a car with a blend because it takes a machine just for recovering blends and they have to pay to dispose of the old blends because they can't be recycled or reused. So the shops that do have that equipment charge a lot to work on them.

If you are going to DIY AC recharge make sure you get the correct refrigerant (IE the exact kind in your car) and read the directions completely before attempting to do the repair yourself.

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The pressure was equalized throughout the system. Static pressure (without the system running) at around 80deg F should be around 90psi. I found this information from this website:

On a properly working system, high-side pressure will be about twice the ambient temperature, plus 50 PSI. For instance, on a 90-degree Fahrenheit day, twice 90 is 180, plus 50 equals 230 PSI. This is not precise but close enough for the purposes of this article. Both pressures reading within these ranges means the system should produce a vent temperature in the mid, to low forties, with the engine idling.

They suggest using a dual gauge manifold, showing both the low and high side. Unlike my esteemed colleague, I believe checking and recharging your system is something which can be done at home. You do, however, need to be careful while doing such, as if you blow the system by overcharging, you will be in for some major repair bills. Also, over charging the system (if it doesn't blow it) can also cause the A/C core inside the car to freeze the condensation.

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  • @interrobang ... If this answers your question, please consider checking it as answered.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Aug 20, 2014 at 22:12
  • I had to give it to @Larry. He answered my question more directly. What did I do wrong? I used the high side instead of the low.
    – sgryzko
    Commented Aug 21, 2014 at 23:58
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I know this is an old thread but I will answer for the benefit of others making a similar mistake. Most of the consumer recharge units will not fit the high pressure port so I think your mistake was simply that you didn't run the engine with the air con set at minimum temperature for 2 mins. With the engine off and the compressor stationery, a healthy system will hold pressure. The 30psi you refer to is the gas pressure with the system running. A closer inspection of the instructions on the recharge bottle should confirm this. Happy motoring.

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-3

The fault for me would be your wasting your money on a Re-Charge kit. A service quality AirCon service machine would not only check pressures and moisture content, but also find any vacuum leaks. The machine would also be able to check high and pressures during actual operation of the AirCon, and replenish any gas or oil with the exact correct amounts.

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    This answer is not particularly useful given that the OP acknowledged in the question that DIY A/C service is generally fault-prone. The question asks specifically what the fault might be in this case.
    – jscs
    Commented Aug 20, 2014 at 20:02

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