Compressor relief valve diagnosis

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Tubularfab
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Compressor relief valve diagnosis

Postby Tubularfab » Fri Jun 26, 2020 10:19 am

Hello - just joined this forum for this question. I am a mechanical engineer and a car guy with lots of wrench time in.

My wife’s 2009 Honda Odyssey’s A/C is not working when it gets above about 75 degrees outside. I’ve put my gauges on several times, and it shows low charge. For instance, 85 degrees ambient and I get about 20psi low, 90 high and virtually no cooling. I add a little refrigerant, and bring the pressures up a bit and it starts cooling better (still undercharged). However, if you drive it it blows off refrigerant from the relief valve on the compressor as soon as the engine rpms rise by the slightest bit, and then stops cooling. I did this yesterday with gauges in place and did not see any jump in the high side - held steady about 120 psi as it blew off the Freon.

So, my question is do I just need to replace the relief valve? Or, can something between the compressor and high side port be obstructed and cause the relief valve to open? To me it seems the it has to be the relief valve, but looking for verification- haven’t encountered this one before!

Thank you!
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bohica2xo
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Re: Compressor relief valve diagnosis

Postby bohica2xo » Sat Jun 27, 2020 6:10 am

Many times, when an HPRV opens it never re-seats properly. I would replace it given the age of the vehicle.

First you should look for why it opened the first time. Are the condensers fans working? That is the number one cause of a high pressure event.

The oil volume lost through relief valve operation is hard to determine. But you lost some the first time it opened.

I would look the system over carefully for any damage. Do you live someplace with a lot of road salt or sea air corrosion?
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JohnHere
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Re: Compressor relief valve diagnosis

Postby JohnHere » Sun Jun 28, 2020 11:16 am

bohica2xo wrote:Many times, when an HPRV opens it never re-seats properly. I would replace it given the age of the vehicle.
The same thing often happens with the Temperature Pressure Relief (TPR) valve on a home's water heater. Although some people suggest testing the TPR valve yearly by manually opening it, I've found that once you do that, it will continue to leak and require replacement. Same thing with the HPRV in this instance. Once it opens for whatever reason, it often doesn't re-seat, as already said.
bohica2xo wrote:First you should look for why it opened the first time. Are the condensers fans working? That is the number one cause of a high pressure event.
I wonder whether the system actually experienced high pressure. It's certainly possible, caused by the fan(s) malfunctioning, as mentioned. I'd definitely check that out first. The compressor was generating only around 120 PSI during your part-charge pressure testing, though, which points toward an HPRV that normally would open at a much higher pressure.
bohica2xo wrote:I would look the system over carefully for any damage. Do you live someplace with a lot of road salt or sea air corrosion?
If you live in such a locale, the HPRV could have corroded to the point of failure, especially if the compressor sits down low. I would change it as already suggested, add some refrigerant (as much as needed to make the compressor run), operate the system for a short time while driving (just a few minutes, though, as a low refrigerant charge will result in low oil flow through the compressor), and see what happens. If the new HPRV doesn't release, then you've probably found the problem.
bohica2xo wrote:The oil volume lost through relief valve operation is hard to determine. But you lost some the first time it opened.
As said, none of us knows exactly how much oil it lost. Any amount added now is guesswork. You could put in an ounce or so at this point. If it's not enough, the risk is oil starvation to the compressor and eventual compressor failure. If it's too much, cooling might be compromised.

The only way to get the right amount of oil in there now is to start with a completely empty system, including an empty compressor, properly flushing the components that can be flushed, adding the correct amount of oil to the compressor/components, reassemble everything, and evacuate/recharge according to the under-hood decal.

Your call.
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bohica2xo
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Re: Compressor relief valve diagnosis

Postby bohica2xo » Sun Jun 28, 2020 11:43 am

Yep.

The very nature of the HPRV leaves the spring & piston open to the elements. Low mounted compressors can have corrosion issues. Either the spring in the valve rusts away & it opens - or the whole mess corrodes & it fails to open at all.

That valve should really be a bypass within the compressor to keep from venting refrigerant. So far no manufacturer does this.
Al9
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Re: Compressor relief valve diagnosis

Postby Al9 » Sun Jun 28, 2020 12:09 pm

Replaced my HPRV on my aging compressor last year. Noticed the new one comes with a green plastic cover in front of the valve "hole", which the old one simply lacks. Likely supposed to keep any dirt out. Anyways in my case it's the o-ring behind that actually failed, yet the compressor is mounted low.
bohica2xo wrote:That valve should really be a bypass within the compressor to keep from venting refrigerant. So far no manufacturer does this.

They're not doing it likely to prevent excessive internal bypass "old and worn compressor" like issues (likely ending in unneeded compressor replacements) in case it fails. Though they could well employ a V5 control valve like design instead of a Sanden SD7V16 control valve like one.
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bohica2xo
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Re: Compressor relief valve diagnosis

Postby bohica2xo » Sun Jun 28, 2020 1:56 pm

Too clever by half.

A bypassing compressor could be diagnosed as any other system issue. A bypass valve would keep the refrigerant and oil inside the system where it should remain. With the laws regarding venting, and the flammability issues of things like yf1234 this should be obvious.

.
Tubularfab
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Re: Compressor relief valve diagnosis

Postby Tubularfab » Mon Jun 29, 2020 10:28 am

Thank you for all the info! This is just one I never experienced before.

The van has lived in Atlanta, GA all it’s life and never saw much in the way of snow or salt. There is no damage to the system,?either.

I guess I will try a new valve as a start. Any ideas what thread the Honda compressor would have, or where to buy one?

Thank you!
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JohnHere
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Re: Compressor relief valve diagnosis

Postby JohnHere » Tue Jun 30, 2020 7:10 am

If it has the original Denso compressor, the thread size is M10-1.5

Check with Tim at ACKits.com for the correct OEM part.

An Internet search turned up this one: https://www.ebay.com/itm/NEW-A-C-Compre ... 4048659882
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Tim
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Re: Compressor relief valve diagnosis

Postby Tim » Tue Jun 30, 2020 7:25 am

Thanks for the reference.

Please no ebay/amazom links on our forum. They do fine on their own. And do not support this site in any manner!

Another note. I've been working on some email server issues. Reply notices should be better now as well as reset emails.
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JohnHere
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Re: Compressor relief valve diagnosis

Postby JohnHere » Tue Jun 30, 2020 7:35 am

Thanks, Tim. Noted for future.

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