My a/c is giving me another headscratcher. The driver side blows ice cold air. The passenger side is 10 to 15 degreesF warmer. This is at startup. I have verified no dccv problem by measuring at startup when heater lines are ambient and even put clamp off pliers on the hoses to eliminate the dccv. I have also checked the acuators and doors for proper function and all is good there. I read thru the workshop manual and have a good understanding i think on how temp is controlled
It seems that the dccv controls individual tems as well as one temp by regulating hot water flow thru the core. As i drive more the vent temps get closer to about 6 to 8F. I have read that the evap core has 3 chambers. Inlet. Bottom back up to passenger side and outlet. I also read in searching this that a low charge can affect the passenger side. That or a partially plugged evap core. I had a saga last year whete i had to replace a line. I found no leaks but a year microleak coild be there. I will start fresh with a measured new charge and go from there. As always any insight is greatly welcome

 

Interesting. I've never heard that, but who knows. Doesn't sound too far-fetched, if somehow related to how refrigerant flows through the evaporator. Perhaps when refrigerant is low, the driver's side behaves a little better? Looking forward to hearing your results after charging the system.

Do you have a link to where you read about this? I'd like to read more and maybe even add more details to the troubleshooting guide.

 

i read about it in the workshop manual in the a/c operation section. Then a bit more online in a ford forum. Sorry no link to that. The manual is the 2004 to 2008 version

 

Found a little tidbit about the refrigerant flow through the evaporator. but unfortunately no mention if one side tends to be favored when the charge is low.

Link to the workshop manual near the bottom of this page, then scroll down to page 2647 of the PDF:

JagRepair.com - Jaguar Repair Information Resource

Copied text follows:

"The A/C evaporator core is the plate/fin type with a unique refrigerant flow path.
A mixture of refrigerant and oil exits the thermostatic expansion valve (TXV) and enters the evaporator tank area through the 12.7
mm (0.5 in) tube.
The tank area is divided into three sections: front inlet, front outlet and rear tank.
The refrigerant enters the evaporator core tank area at the front inlet, flows down through the core and up the back side in a
"U-flow" pattern.
The refrigerant moves into the rear tank area and across to the other half of the core. The refrigerant moves down through the core
and back up the front side of the core to the front outlet tank area.
The refrigerant at this point is in a gaseous state. It exits the evaporator through the 16 mm (0.64 in) tube then passes through the
TXV."



Hmm, I poked around a bit by searching for "Ford AC warm on passenger side" but didn't find anything conclusive. It was painful to read some of the results from various forums, as guys were making expensive blind guesses. I did see a couple of mentions about how poor performance was potentially more noticeable on the passenger side when the charge was low. Nothing definitive, possibly an old wives' tale being repeated, as often happens online. And sadly, no follow-up if a proper charge took car of the problem. (I guess we're not the only forum with a drive-by problem...)

Therefore, in the name of science, it's time for you break out your clipboard and don a lab coat. Measure ambient air and before/after duct temperatures. Service the refrigerant and see if the situation improves. If feasible, don't make other repairs at the same time. The objective is to see if correcting the low refrigerant was the fix, not something else done at the same time.

 

You probaly came across the same ford info i did. It seems by the manual description the driver side gets first dibs then as the refrigerant crosses to the other side the passenger side gets it share. In a perfect world a full charge at operating pressure would be plenty to make the evap loop at full speed and have very little if any temp diff at the ducts. If there is a restriction in the evap it is after the first chamber. I will evacuate and recharge and check temps. The air off evap sensor and the driver and passenger internal duct sensors are one reading and the actual duct discharge will be the other. The evap air off temp sensor is on the drivers side close to the driver duct sensor and they are close in temp. What puzzles me is how after driving some the temp difference decreases quite noticably btween the driver and passenger sensor and gets colder finally on passenger side. I do not know enough about refrigerant dynamics to form any theories on if this is due to extended run time

 

Clubairth has a pretty good understanding of the evap core and has said because of the three chambers a backflush is almost useless to clear a restriction because of the flow pattern. Now it makes sense. Path of least resistance. As for now i am using drivers side vents and rear vents. It cools the cabin surprisingly well. Makes me think the rear vents feed off the drivers side as they are nice and cold

 

Any chance you might have a temperature sensor problem? The system uses several and they are all the same. This is just a wild *** guess!





I know you have worked on these before I think? Sorry I don't have any figures of what the sensor should measure at room temperature. I just check several and if they don't all read the same replace the ones that are different.

Yes that's what I was trying to explain and sometimes you will see it's called a dual path evaporator and it's common on cars with dual climate control systems like what the S-Type has. One additional problem is if you try and flush it you will strand some of that chemical in the nooks and crannies of the evaporator core. That might cause some problems or it might not.

Post some gauge pressures as you say it might just be a low charge condition.
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i replaced the two vent temp sensors. All 3 ohm out perfect and the discharge temps confirm. There is one door called cold air bypass. I am thinking it redirects ambient air to the evap core if needed to prevent freeze up. It moves fine. I will post a couple pressure readings soon. Thanks for confirming evap setup. Like i said the driver side blows very cold. Works great. Passenger side about 15 to 20F warmer but gets to with 6 to 8 the longer the run

 

the bypass door cycles on lowest ac setting

 

I don’t believe a problem with any of the three temperature sensors would cause the unique situation we’ve got here. In manual LO, the two duct sensors are completely bypassed. The evaporator sensor is still in play, but if bad it would affect both sides. In the present situation, only the passenger side appears to have insufficient cooling.

The typical fault causing a split is a problem with the DCCV not responding as commanded, letting unwanted heat into one side of the heater core. However, it appears the DCCV has been thoroughly tested. The lines were even clamped off to prevent hot coolant from reaching the heater core. So even if a sensor was bad, or the DCCV was bad, clamping off the coolant lines should have stopped the temperature split.

i think he is on the right track to investigate the potential low refrigerant charge. I am very interested to learn if low refrigerant can cause cooling to drop off on one side only. My hunch is this only happens if the charge is slightly low.




Sensor resistance values can be found in the climate control troubleshooting guide. Once again, I don’t think they are at fault but can be checked if so desired.




One word of caution there. It can be very difficult to extrapolate the refrigerant quantity from pressure readings. There are so many variables, including whether the compressor has been modified to override the variable bypass valve. A pro might be able to figure it out but I think this ability is way beyond the capabilities of we mere mortals.

 

Yes I have never found a problem with low pressure readings that I could fix without starting all over. As you say the only way to be 100% sure of the refrigerant amount is to vac the system down and fill with the factory amount. I use a digital scale as I have not got a charging cylinder yet.

I would have suggested DCCV a first but he has checked that thoroughly and it does not appear to be bad.
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Got a good friend who is an hvac wizard and has him own company involved. He is well versed in auto a/c also and is familiar with the dual chamber evap core. Commercial hvac uses a similar setup sometimes running 2 coil units from one compressor. We discharged the system using his recovery tank and got 1lb 9 ozs out. About 3 to 5 oz low. Vauumed and checked for leakage. All was great. We put in the stated charge plus the plus 2 ozs as the sticker says you can and then sniffed for leaks as best we could. Got a maybe at the valve cores but he said the oil freon mix left there is probably causing that and to revisit that later.

We went on a freeway drive with him monitoring the 3 in car sensors and duct exit temps. The a/c was working nice but the driver side was still about 4C colder than passenger. He explained why and said now we fine tune. I held the throttle in park at 2000 rpm while he put tiny bursts of refrigerant in. Waited a few minutes to stabilize and took readings. After a few of those we had the sensor temps at the two sides within 2C of each other. Went for another freeway drive and the stayed that way and sometimes equaled out. 3 to 4C sensor temp and pretty much equal in duct exit temps. Very nice now. Checked pressure and high was 275 to 250 at 2000 rpm and low 25 to 30psi. Ambient was 97F. He said the initial fill weight is a standard that meets the needs of the a/c system and to fine tune every vehicle like that would be expensive time wise. We added less than 2 ozs of fine tune refrigerant in the end but wow what a difference. He said fine tuning makes up the difference in the variables involved. Like comp performance. Condensor performance evap and the like. Even slight variations in the refrigerant itself from different manufacturers to affect its properties. I will revisit the valve core sniffing in a couple weeks

 

Ooh, this is exciting. Glad to hear you got it sorted out. I've never heard about "fine tuning" the refrigerant quantity. I usually just aim for the upper limit, to buy me a little extra time due to (normal) minor leakage over the course of several years.

What do you (and your AC wizard friend) think of my theory about how the evaporator behaves when the charge is a little low? I'm still thinking the cooling performance tends to drop off first on the right side but this difference probably goes unnoticed by most people. Heck, my wife usually likes to adjust the temp a few degrees warmer on the passenger side anyway, and would not necessarily notice if a few degrees warmer than requested.

 

your evap low charge theory is spot on on how he described it. One side gets first dibs and then the second. The fine tuning is taken from commercial installs because there is no preset weight charge because of unknown line lengths. He said the little extra refrigerant makes the biggest end change. Occasionally he said you fill a little too much and then back it down