High side pressure lower than static pressure?

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High side pressure lower than static pressure?

Postby brian0918 » Sun Sep 11, 2016 9:47 pm

My 2006 Honda Accord has an ongoing issue with the A/C - it is only blowing cool (65F) on passenger side, warm on driver side. This can be a symptom of low refrigerant because the refrigerant enters the evaporator on the passenger and is only able to cool that side.

I took it to a shop that evacuated and recharged the system and didn't find any leaks. Because of the temp difference they think it's just a blend door problem, even the passenger side is not very cold.

With rented gauges I did this test on a hotter day (88F and sunny):

1. Ambient pressure with A/C off: 105 psi on both sides.
2. Turning A/C on at idle: immediate drop to 65 High, 15 Low.
3. While at idle: High wobbled and climbed to 80, Low would climb to 24, then lower to 16, then back up again. ???
4. Increase to 2000rpm: High remained around 80, Low dropped to 11.
5. After a minute holding at 2000rpm: High 95, Low 14.

Why does the High side drop below ambient? And what could be the problem based on these readings?
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Re: High side pressure lower than static pressure?

Postby ACProf » Sun Sep 11, 2016 11:49 pm

1. Ambient pressure with A/C off: 105 psi on both sides.

Using temp/pressure chart on top post, Static at 105 psi says ambient temp is around 90F

3. While at idle: High wobbled and climbed to 80,

80 psi is about 75F. No heat transfer occurs FROM 75F to 90F.

Your system is way undercharged [or refrigerant leaked out on your drive home].

ACProf
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Re: High side pressure lower than static pressure?

Postby brian0918 » Sun Sep 11, 2016 11:55 pm

Thanks fo the reply. What about the fact that the high side did not increase substantially at 2000rpm, and the low side did not go to near zero or negative? Could it indicate the compressor is failing to build pressure, rather than that the system is simply low in refrigerant?
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Re: High side pressure lower than static pressure?

Postby brian0918 » Sun Sep 11, 2016 11:58 pm

I actually brought it to the shop a week later, and they claim they didn't find any leaks, and their recovery machine didn't find any problems with the system.
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Re: High side pressure lower than static pressure?

Postby ACProf » Mon Sep 12, 2016 7:31 am

If there's nothing more to compress, the high side won't go up!

You didn't mention any previous history on this vehicle to base a diagnosis on.

Original compressor?

Has the system been serviced?

Parts replaced?


I'd get a second opinion.
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Re: High side pressure lower than static pressure?

Postby Tom Greenleaf » Mon Sep 12, 2016 12:01 pm

Quote from top">>
I took it to a shop that evacuated and recharged the system and didn't find any leaks. Because of the temp difference they think it's just a blend door problem, even the passenger side is not very cold.<<"

*********************************
Did the shop tell you how much they recovered and if it worked properly for even a few minutes when/if charged back to spec? They might not be able to and quickly lost refrigerant when pressure might have spiked to norms and just bad luck at finding the leak.

I'll spare the novel and say I think it leaked out already and agree with ACProf - get another opinion. All forms of leak detection used to really verify no leaks. If exact charge came out or does again if it was right unless stolen where did it go?

One more: Check condensate tube for evidence of oil - none should be there,

T
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