Heat exchanger design - Flat vs Rround Tube

[Veritas]

What I wanted to talk about was the design differences between flat tube and round tube design in heat exchangers. Traditional radiator, condensers etc used round tubes. Now however most certainly due to reduced production cost, most all are flat tube. I have a real world problem that has presented this issue.

I replaced the condenser, drier, and compressor on an 04 Ford Taurus. very clean, flushed all lines over an above the call. vacuumed etc at my ambient temp my high side hits the mark while the low side is too low. From memory it was something like @ 90 deg I was supposed to be around 40-44, 200-225 or some such, but when I hit 225 I only had about 25 on the low side. Air was cold, but not right. honestly I didnt take a vent temp, and I should have. It felt like perhaps 60, not the 50 I would expect.

correct me if im wrong but it looks like I need more refrigerant, but I cant because high side restriction. I recharged the OEM system several years ago and it in fact did take more refrigerant.

so, on to my post. My observation is that the newer flat tube designs are more restrictive, than the round tube. I believe that aftermarket manufacturers are using the physical dimensions, and the thermal profile without respect to orifice flow.

has anyone noticed under performing AC, or high side restriction after replacing a round tube with a flat tube design condenser ?

[tbirdtbird]

First vent tamps would help a lot along with pressures. Pressures s/b taken at 1500-1800 RPM with max fan max cool and doors open, ie a load test.
Seriously doubt your problem is the condenser. The modern PF condensers have a way greater fin density which is required for R134, than the old round tube designs.
You can do a rough check of your condenser using your IR temp gun by getting the temp of the pipe into the cond and the pipe out and compare. To me, the diff s/b at least 25°or better yet 30°
A low of 25° corresponds to a core temp of 29°, so your vent air should be cold, maybe a little too cold (the core might freeze over)

I would be looking at
1) has cabin air filter been changed
2) do you have reheating of the cooled air by hot air from the heater core
3) in other words are the blend doors doing what they should

Report back

[Veritas]

Interesting, was unaware that pressures were taken at load. I will get that and the vent temps.

Actually the OEM design is R134a with a dual core, tube condenser; Hence my concern for the single core flat tube. It does have 3 or 4 more runs, but I doubt that would make up for orifice size. Those holes couldnt be more that a few millimeters, the tube is around 8mm I.D. I think I have an old flat tube I can cut up.

*sigh* I will have to get another temp gun. My son left mine out and it 'accidentally' got eaten by a truck tire I have some analog T-stats though.

I'm not aware of a cabin filter, but I could check. I dont feel there is a vent problem, so I will avoid disassembly of the dash for now. I have had this vehicle since it was 30k miles. The AC was reminiscent of R12.. cold. Ice.

3 years ago it leaked down I replaced a few o rings, vacc'd it, charged it, and it was fine about two seasons
last fall the front seal went out, so I put a kit in the compressor. I should have replaced the drier at that time, but, bandaids... the seal didnt hold for whatever reason.

except the evap and the compressor line, everything else was changed. hmm, there is a ?pressure sensor? on the expansion device that is inline. that didnt get replaced....

I just cant fathom how one could expect the same flow through a smaller orifice at the same pressure. These auto parts store brands are lousy I think.

[tbirdtbird]

R134 systems run quite well on parallel flow (PF) condensers, and that is how cars come equipped now for quite a while. They really won't work well any other way. They have a high fin density, thus more surface area for heat exchange. So-called orifice size is not an issue. I am surprised your condenser is of tube design.

Another way to determine if you have reheating is to clamp off your heater hoses and wait about 20 minutes for the heater core to cool down.
Suggest you obtain parts, or at least prices, from the site sponsor, Tim, at ackits.com.
He has quality products at verrry good prices.

In this shop we do not buy from the chain auto parts stores and certainly not auction sites and amazon, most of that quality leaves a lot to be desired

I would double check for a cabin filter, via owners manual or google it. We just had a Camry come to the shop whereby the driver said the freon was low. We are in Texas heat (105°). Vent temp would not go lower than 65°. Although 200K, the system had never been touched. Well the gauge readings were fine, in fact showed the core to be 35°. Of course the cabin air filter, which the owner was not aware of, was clogged badly.
This should help:
https://www.google.com/search?client=fi ... air+filter

[Veritas]

Thank for the good inf tbird, I'm not doubting parallel flow condensers ability for thermal exchange; Rather the modification of the OEM design. Its worth mentioning that phase exchange systems are balanced with numerous considerations.

There are a number of departures on this vehicle. For one, VIN 'S' has the Duratec engine, not Ford Vulcan.They remind me of the Taurus SHO's from the 90's in that, you might find one that has a supercharger, or some luxury feature you wont see on standard models. I'm not talking it up, but I often find information on 04 Taurus' that dont apply to this vehicle.

I will check the manual about the cabin filter. Its possible. My Jeep is the top of the line trim package, and it has the capacity for a cabin air filter, but they are not supplied, even new. True efin story. Owner must install it, at own expense. little over $100 I think.

Anyway, here are the results. I did in fact add a bit of refrigerant.

Ambient Temp: 86 deg F
Test Time: 5 minutes
Low Pressure: 31-36 PSI
HIgh Pressure: 245-290 PSI
Vent Temperature: 62 degrees F

R134a Chart:
Ambiant 85 deg F
Low Pressure: 45-55 PSI
High Pressure: 225-250 PSI

I snapped a few pics of the old condenser.

[Veritas]

Not sure why you keep on about the cabin air filter? Looks fine to me

Seriously, It may be moot with regard to the AC . This vehicle has not discreet recirc control. There is MAX AC, and AC. Max is recirc, while AC is fresh air. You can believe that that and the passenger side gas fill tube are my favorite features on the vehicle.

Of course I must perform the test again. I go to the city on thursday to the doctor, I will try to obtain another infrared thermometer to read the pipe temp.

Thanks for the heads up. It was in fact on the 15k mile checklist. I probably saw it and though it was not equipped.

When I was a kid AC in a car was sticking your head out of the window. Not that cars didnt have AC, but they were usually broken, or the driver didnt want to spend extra fuel to run the AC. I can understand. At .59 cents a gallon, who wants to lose 3 mpg to stay cool when its 95 deg outside?

[tbirdtbird]

Looks pretty nasty!

A lo of 31 psi means the core is at 36°. Allowing for some loss with the heat transfer, your vent temp s/b close to 40-42°

Would be interesting, and helpful to future readers, if you could post your numbers again.
Given the two choices you have, we need the numbers on whatever your recirc is.

I believe your condenser is the piccolo type. Should be OK

Be sure to get the air filter for your Jeep, else your evap will clog up beyond repair. We have changed out several such evaps. A not fun job and very labor intensive

[Veritas]

Again, thank you tbird. the lead 'piccolo' has lead me to condenser design, and a better understanding of the construction of these heat exchangers. And this topic has been discussed numerous times.

I can observe that on a parallel flow there is not one, but multiple orifices in the lines, and that if the orifice area adds up to the tube on a piccolo type, then there should equal flow. Honestly at this point I am having trouble believing that they actually add up. the replacement condenser lines are smaaaall. short of cutting up two direct models, I suppose I will have to choose a side and hope the manufacturers did their due diligence. After all, no manufacturer has ever made an inferior product before

FWIW recirc (MAX AC) was always on during all my charging and testing. I also put all windows down. I recall years ago that was often debated (windows up/down)

So irrelavant stuff about the Jeep:

The Jeep *sigh* yeah. I am seeing some reasonable prices now. around $30 (or less) Perhaps I didnt look hard enough a few years back they were $89-$119! I will check today if mine has the housing equipped. I dont think it does. If not I can stop in the bone yard tomorrow and see if I can dig one up.

Yes, the jeep evap replacement is a terrible job I have heard. These models were affected by the blend door calibration leading to breakage of the blend door(s). the vehicle has separate driver/passenger climate controls. each blend door is controlled by an electronic knob. When the vehicle is off, the BCU 'calibrates' the position by driving the motor and measuring the voltage drop on the motor controller IC, until a certain voltage drop is achieved. Unfortunately, it continues to drive the motor after the blend door stops. To make mattes worse the motor assembly uses a reduction gear design giving it a great deal of torque. Terrible idea for plastic doors. Fortunately, mine arnt broken.

To replace the evap on the jeep: remove the entire dash including the steering column to remove the air box which houses the evap, heater, and blend door assemblies!

In fact, the blend door breakage actually totaled numerous jeeps because the labor is over well over 2k! Thats an old estimate, I'm sure it is much more now the dealer replacement cost was nearly the value of the vehicles is my understanding.

[tbirdtbird]

In most cars, anyway, the cabin air filter is supposed to filter the air into the heat exchanger regardless of the source, but I am not familiar with your car.

[Veritas]

On both vehicles the cabin air filter is in the cowl panel (between the hood and windshield).

It appears to be for fresh air only, but its very difficult to see in. when you pop the panel you just stick your hand in the slot and pull it out, so no idea how its plumbed. I will be glad to have fresh ones in both regardless.

Cheers