AC Coolant Pressure
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Thread: AC Coolant Pressure

  1. #1
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    AC Coolant Pressure

    The wife reported the A/C on her 2008 Oddy isn't blowing cold air. I don't ever recall having the A/C worked on or charging the system. I assumed we were low on refrigerant. Being the wonderful husband that I am, I ran out and bought one of those charge kits with the dial.

    I followed the instructions, started the van, put the A/C on max and checked the pressure off the low pressure side. The needle on the dial shot into the red zone reading approx 125psi. I relieved the pressure, turned the van off and rechecked, getting the same result.

    Rather than risk over-pressurizing the system I elected to do nothing until I hear back from the experts here.

    How is it possible the pressure is so high? Shouldn't it be different with the van and A/C on as opposed to completely off? What's the next thing to look at?

    Thanks for any and all help!

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  3. #2
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    I'll bet you're reading the can pressure, and not the system pressure.

  4. #3
    Registered User dntboles's Avatar
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    I'd stay away from those "charge kits with the dial." It's way too easy to mess up the system. Been there... overcharged that...

    Do a search on the forums for some very recent discussions of others with A/C issues.
    Dave
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  6. #4
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    I agree. Don’t use the cans. The first thing to check is your AC clutch relay. Very common for these to fail. There are 3 identical relays in the relay box under the hood. So you can simply do a temporary swap to see if that solves the problem.
    2010 Honda Odyssey EX-L
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  7. #5
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    125psi could be possible if the compressor is not engaged. Confirm the clutch pulls in and the whole compressor is spinning. If you can see the 3 bolts on the compressor face are not spinning, the clutch hasn't engaged for some reason (fuse, relay, low pressure switch....)

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  8. #6
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    I checked the pressure with the can disconnected. therefore the pressure is coming from the system. I spent some more time on it and the compressor does not seem to be kicking in. I'll try and spend some more time on it tomorrow.

    Thanks for pointing me in the right direction.

  9. #7
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    If your static pressure is 125 psi, than somebody put too much R134 in your system. That said, was the engine stone cold? If the system was warmed by engine heat, than 125 psi is possible.

  10. #8
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    Update: I replaced the relay; $7.00 at the auto parts store. My hearing isn't that great so I couldn't hear the compressor kicking in. But, the pressure is now at 55psi. Per my IR thermometer, the air coming out of the vent was 46 degrees while the outside temp was 57 degrees.

    I would say so far, so good!

  11. #9
    Registered User 0dyfamily's Avatar
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    The only way to ensure correct refrigerant charge is to evacuate the system, check that it holds vacuum (no leaks), then charge with the correct mass of R134a with a refrigerant scale (I have somebody recover the refrigerant, perform repairs if necessary, then pull vacuum using my 5-valve manifold with vacrometer, and then charge from a 30-lb. jug on a refrigerant scale good down to tenths of an ounce).

    Measuring pressure from ports on an unstabilized system is a crap shoot. You need a no-wind area, a way to measure inlet & outlet temperature from the evaporator (I use a multi-channel datalogger), and near-exact value of the local relative humidity before going into the shop manual charts.

    Please, please, please tell me you did NOT use THIS garbage, or anything from this company:



    OF
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    1998 Accord LX 238k, Haynes 676 ATF cooler
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  12. #10
    Registered User dntboles's Avatar
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    Concur with 0dyfamily. That's the correct way.

    I've done the crapshoot, with a gauge set (2 gauges). Sometimes I won. But QA wasn't around to see me topping up.

    However, AVOID the single gauge, low-side only setup that comes with a can of refrigerant. I did that 2 times and thought it was working, until it just didn't. I was 0 for 2 there and then had to take it to a pro to do it right. What did the pro do? Exactly what 0dyfamily said.
    Dave
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  13. #11
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    I had similar issue and had to have AC Compressor / Clutch replaced a few years ago on my 2007 Odyssey LX. I bought the Denso 471-1630 OEM unit for ~$250 and my mechanic replaced it (2 hour job). Money well spent. Beats having no AC in the hot weather!

  14. #12
    Registered User John Clark's Avatar
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    Quote Originally Posted by breinerd View Post
    I had similar issue and had to have AC Compressor / Clutch replaced a few years ago on my 2007 Odyssey LX. I bought the Denso 471-1630 OEM unit for ~$250 and my mechanic replaced it (2 hour job). Money well spent. Beats having no AC in the hot weather!
    The downside of this is that most of the time you do not get any warranty with the compressor if you don't change the condenser and expansion valve(s) at the same time. It's always a conundrum I have to deal with. If you're a shop and you buy from your supplier they will warranty for you as they assume you know what you're doing. If you're not a shop you'll get no warranty if the compressor fails and you didn't change condenser, drier, and expansion valve, as well as prove you did a flush.
    Last edited by John Clark; 04-09-2019 at 09:54 PM.
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  15. #13
    Registered User 0dyfamily's Avatar
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    At least, by going with a genuine Denso for his compressor replacement, breinerd stacked the odds in his favor.

    Our 1998 Accord's OEM compressor quit, with the clutch, pulley bearing and clutch coil dying a terrible death together. I truly feared a "black death" situation, so upon pulling the compressor, I did a post mortem autopsy. Luckily, zero "black death", and it did not internally turn into a grenade, either (no shiny shrapnel inside the compressor).

    Yes, Denso replacement. Did not consider any other.

    I did not pull the condenser and flush it, nor replace the TXV based on the advanced age and low market value of the vehicle...but man, in my burg we need that A/C to work! I did replace the drier/filter/accumulator assembly, as this was the easiest single item to change outside of the compressor, and provides the best "bang for buck" to help assure continued satisfactory operation. Every item that was removed received new O-rings, too. Pulled vacuum, loaded up with the exact charge of R-134a per the shop manual.

    If you don't have a "black death" or shrapnel episode, the odds of a simple compressor replacement working for a solid service lifetime is quite good, as long as you went with proper vacuum application and exact charging after install. Replacing the filter/desiccant is the cheapest additional item one can do to up the odds in your favor.

    OF

  16. #14
    Registered User John Clark's Avatar
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    Yeah, the Denso compressors are the OEM. I just changed two of these out. One on my own van and one on another just like mine. The Denso compressors were identical to the originals, right down to the stickers. The originals didn't even have a Honda sticker on them. On these two vans I replaced everything. If you just have a clutch failure it's tough since they don't sell the clutch assembly separately. I've considered buying the whole compressor and just swapping clutches at times, just so I don't have to bother with the rest of the system just for a coil or bearing problem. I've also seen, however, a bad bearing take out the shaft seal due to excessive heat from the burned up bearing. In that case it's best to replace the whole compressor...but back to the warranty conundrum.

    As a side note, you can't flush condensers anymore. On the outside, the tubes look like they're big. However, the horizontal tubes you see on the outside house much smaller tubes on the inside. The passages through those tubes are so small that you can't flush them. Any small amount of contamination will plug them almost immediately, too. I cut one open just a few weeks back when I did the full system overhauls on the two Odysseys.
    2008 Odyssey Touring-Silver
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  17. #15
    Registered User 0dyfamily's Avatar
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    The HECAT air-fluid hammer flusher will flush a Honda A/C condenser. It's a long story, but I actually have one. It is the only item I know that will push all of the A/T clutch "silt" out of an OEM radiator in-tank ATF cooler, too (there's also a long explanation why some of that stuff will only grudgingly leave its low-restriction cooler).

    Yes, Denso (and Koyo) condensers are thermally efficient, but their design makes them really hard to flush. BTW, most likely a Denso (or Koyo) condenser (representative of most Japanese cars in the last 20 years) is on the far right of this pic:

    AC Coolant Pressure-condsection1.jpg

    Problem is finding a shop that uses a HECAT or something like it. Most A/C shops still only use continuous flow, lower-pressure flushing. If needed, you absolutely need to clean a Honda condenser (or any Denso or Koyo condenser) with a high-pressure air-fluid hammer system, or replace the condenser. The lines downstream to the TXV can be cleaned using relatively lower pressure continuous flow flushing.

    Replacing the TXV is a real linchpin to success if the system was contaminated...its trouble-free function is the least tolerant of contamination, and you can't see the type of contamination that would stop it form working well or at all.

    John, I can absolutely understand why you would replace the condenser (and filter/desiccant in its integrated housing) and TXV to ensure surgical cleanliness for your paying customers, and why Denso demands it.

    I knew I wasn't going to do the extra work to maintain a Denso compressor warranty on a $1,200 car, but I wanted to make darn sure the system was dry so it would work. The last item I installed was the drier/accumulator on that ancient Accord...I readied the parts, dropped the O-rings in a pharmacy cup of ND-8 refrigerant oil, removed the seals on the drier, quickly installed it and tightened the connections, applied vacuum, closed the pump-to-manifold ball valve for a quick leak check, then opened it up and ran continuous vacuum prior to next leak check and charging.

    John Clark, I don't know your thoughts, but that filter/desiccant Honda uses in the Odyssey just is not confidence-inspiring to me. Our old Accord has a real filter/desiccant assembly between the compressor and condenser. It is the size of a 16-oz. Coors Light can for that small-capacity A/C system; it's as large as some I've seen on smaller household HVAC systems.

    I guess this discussion illustrates why that "Can-o'-stuff to 'Fix' your A/C" from the parts store never truly "works", even if it has a fancy gauge on it.

    OF

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