Air Conditioning gauge numbers?
 

I have an old Honda Odyssey minivan that I keep in MN. and I recently had some work done on it including installing a new A/C compressor and (supposedly) refilling it with freon. I was not in town when the work was done and I suspect that the A/C system was not filled completely. I'm going to have someone throw some gauges on it tomorrow morning to check but I can't remember what the numbers are supposed to read?

What are the magic numbers, (low/high), that indicate the system is full? It's going to be around 40 deg. ambient temp when it's checked, if that helps. TIA!

Not sure there really is a "magic number". When it's warmer I always look for condensation building on the suction line and at least a 20 degree or greater split from ambient to vent temps.

What makes you think it's not charged correctly? Not defrosting properly?

35/220 at that temp.

R12 or R134?

Odessy, it's 134.

Why did it need a new compressor? I always question the competency of anyone doing a/c work. That's my gig.

I can't tell you what the numbers should be, but if it has a computer system that recognizes the ambient temperature, it shouldn't even engage at 40 degrees. Your someone may have to send 12v to the clutch coil to get it to engage.

Unfortunately there really isn’t a “magic number.”
And those charts are usually wrong (for example the low side numbers are usually too high, for example, you probably won’t see 35 psi even at 80 degrees ambient).
IMO the temperature pressure charts aren’t actually that helpful as far as telling you when to stop adding refrigerant. Not totally useless, but for what you’re doing, pretty close to useless, and there’s no magic number. (The gauges are very useful as diagnostic tools, and for getting a general sense of the system condition).
The only way to know for sure that it is spot on is to vacuum it down and fill by weight.
Outside of that, IMO the best way is to use multiple factors:
1. Measure and watch output temp.
2. Look for condensation on the suction line.
3. Using a temp pressure chart as very general guidelines to make sure something isn’t way out of whack.

And I’ll defer to Matt, but I would wait til warmer weather to work on it.
Because at 40 degrees ambient my #1 and 2 above won’t work.

Well it will enguage with the defroster, correct?

Thanks, guys. The compressor is engaging for sure but the air coming out of the vents on coldest setting is more or less the same temp whether the compressor is engaged or not. Shouldn't it be blowing ice cubes at this ambient temp? :confused:

It should

Yes, Scott, it should.

Who knows? It may have too much oil in the system now, and that's reason it won't blow snow flakes. Do they know what they are doing? I've had to show repair shops where they went wrong countless times.

Silly stuff, like not draining the new compressor of all the oil.

I do all this work for the DAV, mostly minivans and the number one thing is AC. They come in with the ABS, check engine lights one, wont pass Colorado emissions, and what do they want? Fix the AC. I've replaced so many condensers on Doges at this point I can do it with my eyes closed.

Yes, compressor goes on in any mode when I select the "A/C on" button. I know that I'm not going to be able to get them to evacuate the system and refill it in front of me but I can for sure get them to hook gauges up for me. It has to be filled enough to make the compressor engaged but I think that it's significantly under filled.

Yea, I'm sure they didn't spend enough time with it, AC is such a black magic thing in auto shops. When I worked for Cadillac we had one guy that could work the equipment and they never gave him enough time, you know book time and and all. We had so many comebacks.

That's helpful info, I don't know enough about A/C to tell them what they did wrong. It seems like a really professional shop but I don't have a long standing relationship with them. Had to have them do a bunch of work that I would have done myself if the vehicle was in CA., where my tools are.

New compressors come with oil in them, right? And you are supposed to drain that? :confused:

It's funny because I also had a 2007 Chrysler T&C in MN. and it was fantastic, including A/C. Long story how I wound up w two minivans in a state I don't live in but there it is. Just sold the Chrysler, so down to one. The Honda is a great rig, just needs some maintenance done.

Thanks for responding here.

I'm actually a bit surprised you have AC issues in an Odessey, the system is simple and rock solid. Like Camry's really.

Yeah, I think that it's something simple like the oil or under filled.

Around 2003-2004 Honda put Denso compressors on that had coils that failed pretty often. Once Denso got away from the 10PA17 series, the **** storm with Denso compressors came.

And as you know, a failed coil is not a failed compressor. Too often shops will replace the compressor. I wouldn't. Probably wouldn't even remove it from the car.

It needed a new compressor because the clutch was destroyed on the old one, (made a disgusting noise), and an entire new Denso compressor was about the same price as a clutch. The A/C did not work at all previously. I bought it like that.

I wanted to replace the dryer but it's one piece w the condenser on this model, so I did not. Doesn't the A/C go on at any ambient temp w defrost setting? :confused:

So I am going to see some numbers tomorrow and hopefully get more info from them. I'll look for the numbers that Scott mentioned above. The van is going to mostly sit all winter and obviously the A/C won't be needed but if I wait until spring and it doesn't blow cold, they will just tell me that it leaked out during the winter. I want it working properly now.

Rubber dampner went bad. Been there, have the parts.

I check mine with the normal dash vents, fan speed 2, windows up, recirculate.

http://forums.pelicanparts.com/uploa...1635998472.jpg

This is my sanity check, this was an XJR this summer.

http://forums.pelicanparts.com/uploa...1635998887.jpg

But I start with this.

Could be that there is a leak now and maybe there was before.
The drier is not replaceable? Cripes, who thought of that nonsense.

At the ambient your mentioning? Not really. But it should be colder than ambient. I'd guess at the ambient you're talking your suction side will be 25-35 range without looking at any pt charts.

If it's low on gas, I'd umm... "reclaim the existing refrigerant" and put the unit in a vacuum with a thermistor vac gauge connected so I could see how fast the vaccum was rising and determine how bad the leak is. If the thermistor changes minimally I'd weigh in the proper charge and call it a day.

Ok, put the gauges on it:
 

I brought it by the shop that installed the compressor this morning and got them to put gauges on it. I should have taken a photo but the numbers were ridiculously low, like 100 on the high side and 20 or less(?) on the low side. I was on the way to the airport with a friend in tow who is keeping the van for me, so we agreed to revisit it in the springtime. I just needed them to acknowledge the problem now.

The caps for the Schrader valves were missing and one of them seemed to leak some freon when he disconnected the gauge but it was not leaking prior, the green freon is pretty unmistakable when that happens. My caps are probably sitting on their A/C machine and if the valve is bad, the tech should have noticed it when he filled it. These are the basics. No one ever checked the charge.

I really, really appreciate the knowledge shared by Scott and Matt plus Nick on this thread. A/C is not an area of expertise for me but I'm slowly becoming more fluent in it, thanks to you guys. SmileWavy

That high side is crazy low. I had that happen on an older car and it was a pressure control valve in the compressor that I had to change. No matter what I did the discharge remained low IIRC.

The suction side is a bit low for the ambient but not overly shocking IMO. Valves are a common leak spot. They should have changed the needles when they did the compressor just to take care of a common leak area.

Something else: I don't know if Honda has a sight glass like Toyota puts in their vehicles but if they do that's a great way to tell what kind of charge you have. I'm also wondering if the compressor on your van doesn't have a stuck pressure control valve. I know it's new but from looking, it appears they have this valve in them.

If you run into trouble when you're looking at it in the spring, you've got my number. You're welcome to give me a call if needed.

The caps on the valves are considered part of the AC system. They really need to be in place. Often the caps even have an o-ring.

With pressures that low, the compressor likely should no be running unless it was had a jumper wire on it to force it to run.

It really works best to charge a AC system in 90 degrees and up temps to get accurate pressures.

At first blush I say not enough refrigerant but just tuned into the thread.

I'm looking at Scott's gauges and temp probe and saying over charged. What was the ambient? Must have been 110F.

Denis, that's too low in my opinion, on both sides, it needs more to tell me more. Good thing is, it will suck, but the high side valves may have been hammered when they charged the system.

I don't know how they charged it. I have my way, but it's not the same for an orifice tube car as it is for an expansion valve car. They may have turned the can upside down, or charged as a liquid, and we all know you can't compress liquid.

I would would look at the pressure at equilibrium given ambient temp, and move forward. I can't do that here for you.

Good points mentioned above on the schrader valves, same deal as when you were a kid and had to air up your bike tires in the spring. They can develop leaks, and should be replaced prior to a vacuum. Spit on them, do they bubble? There you go.

I’m betting this thing has a pretty good leak.

About 90 that day if I recall. I was in a nice shaded shop though, and I was blowing air through the condenser.

Did it respond correctly when water was poured on prior, and work well without water after you changed the condenser?

I'm curious. Was in an accident prior, and the body shop put in a 5mm condenser and not a 6? I haven't even looked to see if was a microtube serpentine, or parallel flow, no idea what the car came with.

If that is the case, it should have been discovered when they put vacuum to the system.

A vacuum is just a bit over 14 PSI. Not a major pressure difference. That is why I always pressurizes with dry nitrogen to look for leaks. 50 to psi is not over pressurizing anything and will show you bubbles when soapy water is applied.

Few pros bother with the extra work of using nitrogen.

Well, that would depend entirely on how they did it; they might’ve just pulled a vacuum and loaded the Freon into the system. They may not have actually tested it for a leak.

The capless shrader valves may have been the source. I can't imagine how such a simple step was forgotten.
Not a very big charge in most automotive a/c systems. A small amount missing makes a huge difference in performance.
Not a huge fan of leak checking by vaccuum either. If you do have a leak, the oil charge can become contaminated with moisture. PAG oils are hygroscopic as are POE oils.

Yes, this is the best way by far. At least for me.