2008 Honda Odyssey Touring, Dual rear and front A/C. I had a slow leak I could not find, so after a few years, I decided replace entire system. Initially, I was experiencing 30 PSI on the low-side and 450 PSI on the high-side (which I knew was too high on the low-side), with about 47-49 degrees coming out the vents, but it took a while for the vents to cool down. The ambient air temp at the time was about 89-91 degrees. I felt I had overcharged the system, but it was cooling, so I left it alone for about two weeks. During this time, there were complaints that the A/C occassionally did not work.

Yesterday, I intended to let some freon out and try to lower the pressures. It was 81 degrees outside and I installed the gauges. I ran the car up to 2000 RPM and checked the gauges. I was getting a steady 20 PSI on the low side and 300 PSI on the high, with 44 degrees coming out the vents. I let it run like this for 10 minutes. The pressures never changed. I did not see the rise up to 400-450 PSI like I had previously. So now I was confused and I ended up leaving the system alone. Bear in mind, I replaced literally everything... two evaps, one condenser, two expansion valves, cleaned the lines, replaced all o-rings, same UAC compressor because it was only 12,000 miles old. NOTE: I did not change the high-pressure switch.... I assume its working since the cooling is good on a steady basis and the clutch engages as expected.

Do I have a problem here? why might I have seen 30/450 last week , but only 20/300 today. By the way, there was a A/C not working complaint earlier today when it was 97 degrees outside. But they said it started working again in short-order.

 

You very much have a problem. 400+ psi on r134a is extremely high. Honestly anything over 220 or so is alarming. The symptoms you are experiencing are reminiscent of a blockage or restriction. since you said you replaced your expansion valve, i need you to replace your filter drier as well and receiver. Reassemble, pull deep vacuum and hold to check for leaks, refill with factory charge. Also I am curious to know how you cleaned the lines?

Just for reference I'm not a car AC tech but I work residential HVAC so i am very familiar with the pressure/temperature relationships and where they should be roughly. at 90 degrees outdoor ambient I want to see around 170 or so pressure on the high side within the first 2 minutes of starting the system. The low side needs to be somewhere in the ballpark of 30-40 psi.

When you do the repair and go to test again I want you to record everything down again like you did here with the outdoor ambient. Also, I want you to verify the condenser fan is turning on.

 

Thank-you for your assistance.

1. The condenser fan is turning on. In fact, it seems like it runs too much. Almost immediately upon car start up and AC activation, the fan turns on and off repeatedly with like 1-2 second between cycles. It eventually seems to settle to normal operation. I probably have an issue there as well..... unless its just a symptom of the pressure problems.
2. On this car (someone correct me if I am wrong)... the receiver dryer is part of the new condenser. The condenser has a long cylindrical chamber on the side which contains the drier. You could do maintenance on it if desired, but I just replaced the entire condenser.
3. I cleaned the lines by spraying the cleaner at one end and then blowing them out with air. But it was a difficult process and the cleaner was absurdly expensive in my opinion. I only used one can and I skipped some of the lines. That was the weak part of my job. I am pretty sure everything else was brand new.
4. I bought my parts through Rockauto.com..... and they screwed up the order at several points.... sending me two major components that were damaged and had to be replaced. Maybe the parts they are selling are crap. Unfortunately, its a lot of work to re-gain access to things like the two expansion valves (front and rear AC systems).

I did a careful job of reassembly. I replaced every seal and component. I never looked to verify that the new condenser actually had the drier element inside.... I assumed it did. I did not want to open the drier chamber and look. I figured that these components come with factory seals..... why force the consumer to destroy the seal unnecessarily.

But you identify a much larger problem.

Might simply over-charging lead to my symptoms?

By the way.... the system does not work well. Sometimes cools. Other times, wife complains. Nothing like it used to be from the factory.

So if I do what you ask..... I dont know what I am looking for. But it sounds like I should do two things..... cleans the line professionally and properly..... and replace the expansion valves yet again. Maybe my line cleaning effort just loosened some dirt which is now causing a blockage.

Marc

 

One other thing. Is it possible to add too much oil to the system? I added oil at various locations in the system according to instructions, in order to ensure a good distribution. But I never verified the amount of oil in the compressor.... so I added more to the low pressure side just before closing it up. I added half of what was called for in the compressor. You could assume the compressor (which I did not change because it was only 12,000 miles old) retained some oil from before I disassembled the system.... but I wasn't certain.... so I added more just before I closed up the system. After time, all the oil in the entire system should distribute and even out, right?

Marc

 

And one other "one other" thing. Really a question. Judging from your comments, it sounds like, generally speaking, over charging a system would lead to both low and high sides reading higher pressures. I have a situation where my low-side is LOW at 20, and my high-side is HIGH at 300. I am thinking, removing some freon might resolve the high-side problem, but probably will not fix the low-side problem.... or might make it worse. In other words, I am thinking that adding or removing freon is like the adage that a rising tide lifts all ships. It will have an equal impact on both the low and high sides. So regardless of freon levels, I have a "relative" pressure problem between the low and high sides. I do think I over-charged the system however. I was using a large $100 container of freon I purchased several years ago and I have been using it for AC maintenance for several years. I was going by weight and had the container sitting on a scale. But the freon went much faster than I expected and, before I knew it, I had passed my weight marker.

Marc

 

An overcharge will result in higher pressures on both gauges. If you try to recover charge until you get a 170 high side, your low side will probably be very low. This is indicative of a restriction. Think: compressor is pushing refrigerant into the condenser, but a restriction somewhere is preventing it from moving through the lines as fast as normal, so pressure builds up behind this restriction. Simultaneously, since more refrigerant is backing up in the condenser there is less elsewhere (evaporator and suction line) and so the low side pressure decreases.

As for the oil I would follow the OEM instructions. I can tell you however that in residential when you change a compressor you don't have to make adjustments to the oil in the system. There's always a little oil in the lines and evaporator but the large majority is in the compressor. I'm sure a car would be similar. So by changing a condenser in a car, you should NOT have to add any more oil into the system. By changing the compressor, you also don't have to adjust oil. You really should never have to adjust oil especially if you're replacing the compressor.

I tried looking up a picture of the condenser for a 2008 odyssey to see what you're talking about. I don't see what looks like a reciever but the photo was kinda small. There is a restriction somewhere in the high side after the condenser. Its either the expansion valve, or its the reciever drier. I got money on the reciever.
Pull vacuum for a long time to ensure the moisture is out of the system. Sometimes moisture can freeze in the metering device and cause it to restrict. When you shut down the system and it thaws, the problem will go away for awhile upon system startup but will probably show up again.
Factory charge and don't go over. Make sure to purge your refrigerant hoses of air, then zero the scale. On a house I leave the hoses in a deep vacuum (since they are already connected to the system which is also in a vacuum) and release the refrigerant from the condenser so that it gets sucked into the hoses as well, and no air is introduced in the system. When adding charge to the system in a vacuum you would screw your r134a hose onto the jug, then open the jug and go to the other end of that hose and unthread it a bit and wait until refrigerant starts escaping, then screw it back on the gauge manifold, set everything in place and zero the scale. Then charge.

 

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OK.... some feedback. I ran the car at 1500 RPM and let the A/C run a bit. Then the gauges were steady at 20 Low and 200 High. I then removed refrigerant slowly and watched the high pressure fall, while the low stayed steady at 20. I stopped when I achieved 20/175. So.... interestingly, the low remained steady at 20. The cooling improved. I stopped at this point because I did not want to accidentally remove too much refrigerant and have to replace it. I can take more out later if need be. What do you think about those numbers?

One of the big improvements was that now the system cools nicely when I am at idle. Previously, I had to tolerate little or no cooling at all while sitting at a traffic light.

If my problems return, I will double back to your recommendations. I am going to give it a few days and see what happens.

Marc S.

 

Here is the condenser with the integrated drier mounted on the right side.

 

you can try removing the charge and pulling another vacuum. Remove charge, connect vacuum pump and run for 45 minutes. Shut off vacuum, come back in 10 minutes and check that the pressure didn't change. Add charge to system in accordance with the sticker under your hood or in the service manual. Since you replaced most of the system this is the only thing else I can think of doing. That and making sure your fan is blowing strong in the vents in the car.