What happens when capacity of system is exceeded?

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tbirdtbird
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Re: What happens when capacity of system is exceeded?

Post by tbirdtbird »

This thread is bouncing around and becoming hard to follow, so many cars are mentioned.

Did this car ever perform well for you?
Please give again lo/hi at 1500 RPM with 100° ambient.
Type of condenser??
Any lines close to exhaust?
Any re-heating issues at evap? Are you sure?
Use IR temp gun to slowly go from top to bottom of condenser. What is happening. A properly functioning coil of any type should give at least a 30° drop
Cabin air filter?? If so, when last changed?

In traditional HVAC it is possible to determine the BTU rating of coils and TXVs. Much harder to get this info for MVAC. Would love to know if TXV is sized properly. They are often 1.5 tons
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cyfi66
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Re: What happens when capacity of system is exceeded?

Post by cyfi66 »

tbirdtbird wrote: Wed Aug 25, 2021 12:03 pm This thread is bouncing around and becoming hard to follow, so many cars are mentioned.

Did this car ever perform well for you?
Please give again lo/hi at 1500 RPM with 100° ambient.
Type of condenser??
Any lines close to exhaust?
Any re-heating issues at evap? Are you sure?
Use IR temp gun to slowly go from top to bottom of condenser. What is happening. A properly functioning coil of any type should give at least a 30° drop
Cabin air filter?? If so, when last changed?

In traditional HVAC it is possible to determine the BTU rating of coils and TXVs. Much harder to get this info for MVAC. Would love to know if TXV is sized properly. They are often 1.5 tons
The performance has always been the same - excellent in every season except summer :). I have never been happy with it especially since getting my Nissan and seeing how good it can be, I have had the car for 4 or 5 years now.

The system is completely factory and has a parallel flow condenser. Has been thoroughly cleaned and fins toward the bottom where the most impacts were were straightened.

Radiator fan was upgraded to hydraulic type from the Celsior (Japanese version of the LS400). This uses a hydraulic pump to drive a hydraulic motor that drives the fan. Much more airflow at low engine RPMs.

Lines are not any closer to exhaust than any other vehicle. Not a lot of heat gain in the suction line its "cool" not "cold" all the way from the firewall to the compressor.

No reheating, I can turn the AC off and I get ambient temperature air. Can also visually see the heater valve actuating correctly. When the system has been running a long time and is nice and cold inside, the suction line at the firewall is "cold" not "cool" anymore. Whenever I have good AC inside the suction line is "cold", whenever it is not good inside the suction line is "cool". As long as the EVAP is getting flooded I am getting nice cold air, the problem is it takes a long time for that to happen.

When you ask for the pressures, condenser temperatures ETC. how long after starting the AC heatsoaked should these be taken? Like I said after 15 or so minutes it working pretty good. First 10 minutes it is not. So should I get my readings during the first 10 minutes? How long after starting up the engine/AC?

Will report back with numbers.

Cabin filter is replaced every few months and is perfectly clean. The airflow rate from the vents is good, just not the temp.

I have some wireless Testo smart probes that I have rigged up to give me live pressure data and can be datalogged. I can get a datalog from heatsoak if that is useful data. Also can log vent temperature.

Temperature drop from condenser inlet to outlet would only be possible if subcooling was happening right?
Last edited by cyfi66 on Wed Aug 25, 2021 1:22 pm, edited 5 times in total.
cyfi66
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Re: What happens when capacity of system is exceeded?

Post by cyfi66 »

DetroitAC wrote: Wed Aug 25, 2021 11:53 am I wouldn't worry too much about cross charged TXVs, they are not going to fix your 99 Lexus performance.

Seems like the Lexus has a 10PA20 compressor (200cc/rev swashplate/piston type), that's good news, but what is the pulley drive ratio? and the Idle and engine running speed of your Lexus?

The volume of suction gas your Lexus is moving absolutely matters. If the Lexus has a 200cc compressor, 1.5 drive ratio, idles at 800 RPM, 1800 RPM at 30 mph, great performance should be possible (with everything else in good order). If it has a 1.0 drive ratio, idles at 400 RPM, 1100 RPM at 30 mph, then suffering will normal. I'm just making up numbers, trying to make a point.

Compressor suction gas displacement in cc/minute will correlate directly to A/C performance. The car with the biggest number performs the best.

It's almost like the glory days in the 60's and 70's with muscle cars. The car with the most engine displacement probably wins the most street races. You show up with your 302 Ford and pull up next to a 429 Ford, guess who's going to win.

Edit: by the way "solid liquid" is exactly how I say it too, and then non refrigeration people are like "Whaaaaat?"
I will have to measure the crank and AC pulleys to figure out the drive ratios. They are pretty hard to get at from the top so I will see if I can reach them. As mentioned before though no increase in engine RPM makes any noticeable difference. I can hold the engine at 4K RPM and it wont get cold fast at all.

My Nissan 2017 370Z gets cold within a minute and outputs very cold air consistently even at low RPM's.
tbirdtbird
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Re: What happens when capacity of system is exceeded?

Post by tbirdtbird »

"So should I get my readings during the first 10 minutes? How long after starting up the engine/AC?"

Let's say 5 min

I am thinking the TXV is not metering adequately after crunching all this info

I am seeking the low side pressure and vent temp to double check on re-heating

Wonder if the Lexus forums would have anything pertinent. I posted a link that covered the EPR only on your other thread
Might be more out there.....

"Lines are not any closer to exhaust than any other vehicle."
I don't know what this means. You are seeking better performance so it would be worth careful consideration. We don't care about other vehicles.
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bohica2xo
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Re: What happens when capacity of system is exceeded?

Post by bohica2xo »

Detroit has a great point about the drive ratio issue.

Had an Explorer that was miserable unless you manually shifted it to keep the engine speed above 3200rpm And the auto trans was shifting at 1300 all the way to OD around town. I gave up and put 4.56 gears in both ends of it.

Try driving your Lexus at 25 to 30 mph with a lower gear selected. Looking to keep the engine over 2500 rpm for that test.
DetroitAC
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Re: What happens when capacity of system is exceeded?

Post by DetroitAC »

Yeah, but I made all my comments before I knew this car has an EPR in the suction line. That thing is unbelieveable to me, I can't understand why they would put in an awesome 200cc compressor and then contantly choke it with this thing in the suction line. To me, it's a sin, unforgivable, suction lines need to be big and smooth and allow flow with minimum pressure drop. Putting a giant restriction in there is a sin, limiting the suction pressure and flow at high loads is a sin.

Your friend's Ford Edge will run the suction pressure far lower than your Lexus at high loads, the Edge will use it's full compressor displacement. This Lexus will be choked by that EPR especially at high loads, at low loads this thing will work perfectly to keep the evaporator from freezing. If you lived in Northern Europe this is a great system, if I lived in Tucson I would take this EPR out and have a contest to see how far I could throw it, make a new low resitance suction line, cycle the compressor clutch with a thermistor like a proper Arizonian.
cyfi66
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Re: What happens when capacity of system is exceeded?

Post by cyfi66 »

Lexus AC datalog.png
Lexus AC datalog.png (128.07 KiB) Viewed 4422 times
Collected data on the way home today.

1999 Lexus LS400 - 108 deg F Ambient - Start from heatsoaked (interior temp 160deg F)- Windows open blower speed max recirc heater hoses pinched
First 3 mins: 1500 RPM stationary
middle: City driving, stoplights etc.
Last 2 minutes: 1500 RPM stationary

Keep in mind the left vertical axis is for high press only, right axis for low press/vent temp. Heater hoses were pinched off for good measure.

Towards the end I got out and felt the suction line exiting the firewall, it was cool but barely, if I had to guess, 60-70 degrees F. The entire datalog is with the windows open and 108 degrees outside, so yeah it was a hot drive home. Normally with the windows closed the vent temp will come down into the 40's after about 10-15 minutes.

The system was just evacuated and recharged with 24oz of R134a about a week ago. Everywhere the high side is peaking was when I came to a stoplight/was idling. You will have to ignore the noise on the low side reading I don't know why it was jumping around so much. The pressure sensors are sensitive to heat so they don't do super well in the engine bay. It would probably also make more sense to stretch this out width wise more because its a 20 minute log of data scrunched into a small chart.

Here is a link to the raw data if you so desire to look at it.
https://docs.google.com/spreadsheets/d/ ... ue&sd=true

The low side pressure port is between the evap and the EPR valve
tbirdtbird
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Re: What happens when capacity of system is exceeded?

Post by tbirdtbird »

I was hoping we could get similar data with the windows up and blower on recirc, so we could see what is happening to the cabin, not while trying to cool the environment down

I myself would like to compare lo side pressure to vent temp
3 data points would be nice, 5 min, 10, and 15 min.

Yes the heater hoses are clamped but I have done that and it is hard to clamp them fully tight and I have been misled.....

I also still think your TXV is under performing

What about using one of those folding aluminum foil backed shields I see ppl use over their windshield and dash since you park in the sun
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B52bombardier1
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Re: What happens when capacity of system is exceeded?

Post by B52bombardier1 »

Hello,

Very interesting data chart and I applaud you - really, I do. My data about vent temperatures comes from my sweaty forehead and a meat thermometer stuck into the center dashboard vent. Sorry, no logged pressures. A few weeks ago here in sweaty Louisiana and after reading a few things around here, I decided to mist the condenser in my El Camino with a little water to see if my sweaty forehead and forearm could tell any difference.

Well, it did make a difference of maybe 2-3 degrees on the meat thermometer and my skin. This told me that my system performance is probably constrained at the point of shedding heat at the condenser and a pusher fan in front of the condenser might help.

In went a seven inch pusher fan that consumes about 80 watts of electricity. I can now dependably reach a 35 degree vent temperature which is a five degree improvement.

Maybe your vehicle could use a pusher fan????

Rick
1970 Chevrolet El Camino 5.3 L LM7 Truck Engine & 4L60E Transmission
DetroitAC
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Re: What happens when capacity of system is exceeded?

Post by DetroitAC »

Nice looking data that shows bad looking things :D

I think your TXV might be having a problem, or maybe you have a clogged filter upstream of the TXV, or something else, because I still don't understand exactly what this car uses for an expansion device, you've mentioned a pressure regulator. Your evaporator superheat looks too high to me, but I don't know how much suction line superheat this is designed to produce with the integrated IHX in the evap core.

Is your liquid line medium-hot from condenser out to the firewall?
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