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AC low pressure is high

All, I have a 2007 Honda Odyssey. The AC stopped working so I hooked up a pressure gauge from one of the self charging kit with the engine off and the pressure was 100 pounds. I let out pressure and only air was coming out and sometimes it was warm air and at times it would be cool for a second or two. Got the pressure down to about 30 pounds.

Started the van and ran the AC on high and pressure immediately jumped back up in the red zone within 20 to 30 seconds. Let some pressure out, and again only warm air came out. Does this mean I am sucking air from somewhere? What should I be checking? I don’t have a gauge to check the high pressure to see if it is normal or not.

Put everything down, and step away from the vehicle.

Because, you don’t know what the hell you’re doing!



There could be a problem with the charging port and what you were reading was can pressure or the compressor was not engaged which would mean static system pressure.

Don’'t take this the wrong way but I agree with Tester. You are wading into something that can not only damage the system but could easily cause damage to yourself such as frostbite or blindness. I think you are asking, or begging, for trouble based on what you have posted.

You likely have never seen a refrigerant explosion. It can be downright nasty and dangerous.


With the engine off or the compressor off the low side will be the same as the high side, don’t release the refrigerant based on this.

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That makes as much sense as cutting your wrist because your blood pressure is to high


I could not agree more !!


While I agree I don’t know what I am doing, all this badgering makes me think the compressor is dead. I was not adding more refrigerant, to be clear. The charging kit has a trigger release, this is how I was releasing pressure. So was not simply pushing the low pressure valve.

If the 100 lbs of pressure is normal static pressure and only air is coming out of the low side, this would be a compressor problem, right? When I turn the AC on I can hear the clutch engage, but thinking maybe the shaft broke in the compressor or something like that. Running the AC after getting it down to 30 lbs by letting air out it when right back to 100, so does that mean other components are working or what would you check?

Looking for pointers, and will be taking it to shop, but wanted to a bit of troubleshooting as that is my nature. I don’t see how anything I did would have caused damage to anything, as far as I could tell there was refrigerant, or at least nothing I could detect being released.

The collective wisdom on this site is that you should stop fooling around! You are apparently unable to hear that.
I recommend that no one give any further response to his questions. If he were to be injured because of something recommended here…(fill in your own negative outcome). We don’t let our kids play with fire. He can go directly to AC professionals and ask all that he wants to.


Stop being foolish. Pointers from the web ! The shop you use does not want to here them and certainly will not want you to say you saw something different on the web then what they say. As for releasing something into the air , if you did that could be a federal charge under EPA rules.

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I recommend that you stop recommending your opinion. There are probably hundreds of suggestions given on this site monthly that could end in disaster. I did not realize that this site was only for professionals.

As a novice, there is no way to gain any understanding of the AC system if it will not be discussed. Not sure what the point of your post was. What have I done that was dangerous? Please tell me. I am not trying to charge the system, I am trying to understand it.

Some of the replies have, indeed, been brusque. They should have told you why what you are reporting indicates that you are working on something where you don’t understand the hazards. I know little, but I’ll give it a try. The knowledgeable people can jump in and correct me.

“I hooked up a pressure gauge from one of the self charging kit with the engine off and the pressure was 100 pounds.”

No way should the pressure on the low side be that high. Either the system is screwed up, or you are measuring things wrong.

“I let out pressure and only air was coming out and sometimes it was warm air and at times it would be cool for a second or two.”

If you were letting pressure out through the port, then you were releasing refrigerant, not air. As the refrigerant expanded on release, it cooled down.

I’m not sure what the actual hazards are. However, if you keep trying this knowledge-free DIY repair you risk messing things up to the point where you will require much more extensive repairs than if you just wisely take it to a professional now.

Thanks Art.

I don’t think I am measuring wrong, but who knows. When I connect the gauge to the low side it jumps right up into the red zone at around the 100lb mark. If I press the trigger on the release it seems like only air is coming out. There is no smell, oil substance and it is not cold at all. The reason I did this is that it was reading very high with the engine running as well. It had been working fine until yesterday then today, no cold AC.

I was not attempting a repair, and while releasing refrigerant is bad for the environment and illegal, I don’t see how it was dangerous. This vehicle has only been in the shop 3 times since I purchased it and it now has 220k miles on it. One of the other times it was in the shop was for the AC about 60,000 miles ago and the compressor was replaced at that time. I have done the timing belt twice myself, brakes myself, oil changes myself and many other misc repairs but in general I never touch the AC. At my age not even sure I would attempt the timing belt again to be honest.

That is incorrect. The car wasn’t running, the pressure equalizes throughout the system.

OP, you have done two incorrect things: trying to diagnose the system when it’s not running, and venting freon, a major pollutant, into the air. Why are you surprised that folks are telling you to stop? I have a full set of gauges, installed the a/c system from the ground up on my first car, and I will still take my car to an a/c specialist is there is something wrong. PLEASE do the same.

Thanks for the info. I was not trying to diagnose it only with the car not running. As stated the pressure was reading high when it was running as well. That is, there was no change. Also, note that as far as I could tell it was not venting freon. I understand everyone’s concern. I get it, it is not something for the novice. But I have already learned a lot from this discussion from those that took some time to explain a few things to me.

Once again, not trying to fix it, just trying to understand it. The last time it had an AC issue and I took it to a shop it was the compressor but they also replaced the pressure switch and a relay. In the end they told me all 3 were bad. This is hard for me to understand, but I do get that it is possible. So before taking it somewhere, wanted to understand what the overall problem was. That was the reason for the post. I am not trying to repair it.

Anyway, enough said, and understood.

I understand you want to figure out what is going on. Here’s one thing you can take away: an a/c system will probably not exhibit excess low side pressure from too much freon if it had been running fine, then quit. The excess pressure is caused by something mechanically wrong in the system. That is, unless you overfilled the system right before, and you didn’t do that, correct?

It’s difficult to pass up the opportunity to be comically critical at times @blevebass_173667. Maybe my best advice is to get a good book on how AC systems work. Until then just leave your cars AC alone.

Thanks all. I have the factory manual, so I should visit that.

Oh, I never tried to charge it. No can was ever hooked to the gauge and hose. I have a 2007 Ridgeline that I can try my gauge on to see what the behavior is on something that is working. If it doesn’t work after that, then I know it was me :slightly_smiling_face:

The high and low side fittings should not be interchangeable so I assume no one has dinked around altered those. As I mentioned previously, a 100 on the low side could be can pressure or static pressure from the system.

As for the refrigerant/air released from the system it should be cold if it is refrigerant only. Not cold could mean all of the refrigerant has been lost due to a leak and you are releasing air pressured up by the compressor.

I’ve offered advice to DIYers on here before. The reason for hesitation here is that your post came across as someone who as about to get themselves hurt. Over the years I’ve seen 4 or 5 A/C explosions; all while in the hands of competent A/C techs. Most were hoses that let go. Two of them involved can explosions in which the very competent and well experienced techs had brain hiccups and inadvertently opened the high side of the gauge set. There was a shotgun boom and they disappeared in a cloud of steam. Luckily they were not hurt due to long sleeves, gloves, and goggles. Refrigerant can cause frostbite in seconds and blindness in an instant if one bit of refrigerant hits the eyeball.

If you must proceed with this please; gloves and goggles. Those are cheap. Fingers and eyes are not.

And for what it’s worth, I consider myself to be proficient in A/C work and still suffer the effects of frostbite on my right index finger. Went some years ago to look at the central unit at my son’s house. A 108 at the time and in a dripping sweat fog I inadvertently got a 1 second blast of R22 on the fingertip.
That was about 8 years ago and that fingertip is still numb. No gloves and I knew better but hey I forgot to bring them and I know what I’m doing so what could go wrong…


Could you perhaps link to this charging kit? Because every DIY A/C charging can I’ve seen involves a hose with a gauge that’s connected to can of refrigerant with a trigger on it (like a can of compressed air). If that’s what you have , then when you press the trigger, you’re definitely adding refrigerant. If you were venting the system, then you’d know it, refrigerant/oil would spray out and get all over the place.

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Great, thanks. I did just hook the same gauge up to my Ridgeline and it behaved as was being described here. With the system off the reading was 80 or so pounds. Started the engine with AC on high and it immediately dropped below 50 between 40 and 50, so lets say 45. When the AC would cycle it would drop down to 10 or so.

On the system that is not working, it is always at 100 pounds. Never drops, so from what I am reading here is that my static pressure may be a bit high (compared to my Ridgeline), but the key is that there is no change which means there is something clogging the system or the compressor is bad. The clutch does engage and disengage when I toggle between AC on and off.

Next will be a visit to the shop. Thanks to all that took the time to give some guidance. In my line of business if something does something to mitigate an issue and it is no longer reproducing it is considered a miss if the cause is not understood. So, it is in my nature to try and understand. I do take all the warnings to heart. Besides possibly releasing freon, which I am still not sure I did, the exercise was relatively safe.

As a side note, I have the charging hose because I put a rebuilt long block into my F350, and needed to charge the AC. That went with no issues, but now I will be a lot more careful based on the information here.