AC Not working. Refrigerant pressure too high.
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  1. #1
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    AC Not working. Refrigerant pressure too high.

    My ac broke about 18 hours after buying it. It worked great on the test drive a couple of weeks ago. It was weaker a few hours after taking it home. The next day it didn't work at all. I was going to try refilling the refrigerant with a kit from walmart. The kit has a gauge. I ran the car and ac on full blast for five minutes and connected the gauge to the low pressure valve, it actually said the pressure was too high. Any ideas?

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  3. #2
    Super Moderator Steve in Chicago's Avatar
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    Even though your engine was running and the AC was turned on, your AC compressor may not have been engaged. If the compressor is not engaged and spinning, your gauge is only measuring the static pressure of the system and not the working pressure.

    Look at your AC compressor. With the engine on, the belt and pulley will always be spinning. The center of that pulley (face of it) spins only when the compressor is engaged. If the system charge is leaking out, when it gets low enough a safety switch will keep the compressor from engaging.

    If your system charge leaked out in 18 hours, how long do you imagine your re-charge will last?

    Your going to need to find and repair all the leaks first. This typically requires you to open the system to atmosphere. In order to do that you'll first need to reclaim all the charge left in the system. Then once you get things repaired and re-assembled, you'll need to evacuate the system before it can be recharged. You're not equipped to do this.

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    It probably leaked out over the course of at least 3 weeks, if not more. The canister I bought also has a leak sealant. Will it work? I don't know, but for $25 I'm willing to give it a shot.

    Thanks for letting me know about the pulley. I'll have to see if the face of it is moving.

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    Super Moderator Steve in Chicago's Avatar
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    Quote Originally Posted by Branson View Post
    The canister I bought also has a leak sealant. Will it work?
    Don't use it. Do some general Google searches and reading on the topic.

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    If the gauge said the pressure was too high, it did not leak out. It's been a while, but I would guess a full system would be around 90psi with the system shut down. It is possible the system was overcharged or had moisture in it and the high pressure shut it down.

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    Super Moderator Steve in Chicago's Avatar
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    I'm guessing his gauge indicated high pressure because it was measuring static pressure and not the suction pressure of a working system. Those DIY simple gauges try to do the thinking for you by giving you a "green zone" to shoot for. Unless the compressor is running, the "green zone" means nothing because what you are measuring is the static vapor pressure of the r134a in the system. The compressor needs to be engaged to get a meaningful reading.

    The static vapor pressure of r134a is temperature dependent not amount dependent. At a given temperature, a can 95% full will have the same static pressure as a can 5% full.

    Running suction pressure could be somewhere around 30psig (depending on temps and amount of charge). Static pressure of the low side could be around 90psig (depending on temps alone) and the gauge would be indicating way above the green zone.


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    Quote Originally Posted by Branson View Post
    It probably leaked out over the course of at least 3 weeks, if not more. The canister I bought also has a leak sealant. Will it work? I don't know, but for $25 I'm willing to give it a shot.
    Listen to Steve. Don't do it. Not only won't it work, you'll never get that gloop out again.

  9. #8
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    The compressor is not running. The bottle was smart enough to base the target psi on ambient temperature and not just just 'low', 'good', and 'high'. The static pressure is 100psi in 85 degree weather. I know static is going to be higher than running pressure, but shouldn't that static pressure still indicate that there is enough refrigerant in the system that the compressor is not shutting down from a lack of refrigerant? What other reasons could make the compressor shut down?

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    Don't overlook the obvious. I've had the compressor fail to engage a couple of times; once it was the relay, once it was the power lead to the compressor clutch. I understand a bad pressure switch is a popular failure mode, too.

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    How would I test for a bad pressure sensor? Vag-com?

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