Air Conditioning gauge numbers?

speeder · 11-03-2021, 06:57 PM

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!

cabmandone · cabmandone's Garage

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?

Scott R · Scott R's Garage

35/220 at that temp.

javadog · 11-03-2021, 07:20 PM

R12 or R134?

Scott R · Scott R's Garage

Quote:

Originally Posted by javadog

R12 or R134?

Odessy, it's 134.

mattdavis11 · 11-03-2021, 07:43 PM

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.

McLovin · 11-03-2021, 07:46 PM

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.

McLovin · 07:51 PM

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.

Scott R · Scott R's Garage

Quote:

Originally Posted by mattdavis11

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.

Well it will enguage with the defroster, correct?

speeder · 11-03-2021, 08:07 PM

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?

mattdavis11 · 11-03-2021, 08:08 PM

It should

mattdavis11 · 11-03-2021, 08:10 PM

Yes, Scott, it should.

mattdavis11 · 11-03-2021, 08:13 PM

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.

Scott R · Scott R's Garage

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.

speeder · 11-03-2021, 08:24 PM

Quote:

Originally Posted by Scott R

Well it will enguage with the defroster, correct?

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.

Scott R · Scott R's Garage

Quote:

Originally Posted by speeder

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.

speeder · 11-03-2021, 08:32 PM

Quote:

Originally Posted by mattdavis11

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.

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?

Quote:

Originally Posted by Scott R

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.

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.

Scott R · Scott R's Garage

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

speeder · 11-03-2021, 08:39 PM

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

mattdavis11 · 08:49 PM

Quote:

Originally Posted by Scott R

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

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.