Rear A/C not working

[Bubba2333]

Hello Everyone! I have a 2018 Ford Flex SEL 2WD and when I have my front A/C on it blows nice and cold (45 degrees) without any issues but as soon as I turn on my rear A/C for the back passengers the air from rear vents blows warm (roughly 75 degrees) and at the same time also makes the front A/C vents blow warm as well. As soon as I turn the rear A/C off the front vents go back to blowing cold again. We have recently had the system vacuumed and freon levels checked. Mechanic says they are at the correct levels. I have checked the forum and some users recommended checking the blend door in the rear for a clicking sound but I don't hear any strange clicking noises. I'm able to adjust the rear vents to hot and the air starts to blow hotter but when turned back to cold they still blow the warm 75 degrees. Could this be a blend door issue? Also both the front and rear blower motors produce a nice strong air flow. I really appreciate the help. AZ summers are brutal without air for my kids in the back.

[Tim]

I suggest using a scan tool and create the issue and see what trouble codes are returned. Record any trouble codes that are shown.

Also, record your pressure readings, both low and high, when the front unit is on and cycles. Then, create your issue, second it, and post the findings. Something like this will take some data gathering to pinpoint the issue.

[JohnHere]

It's normal for the front vent temperature to increase a few degrees while the rear A/C is turned on, but not to the level you mentioned. You didn't say what the pressures are and how much refrigerant was put in, but I suggest double-checking the latter because it still might be a little low on refrigerant. If not, then additional troubleshooting is needed as already mentioned.

[Bubba2333]

Tim and Johnhere I really appreciate the quick response. Ok I just pulled out my gauges and with the front A/C on (no rear) my low side reads (35 psi) and my high side (250 psi). Current outdoor temperature is 100 degrees with 25% humidity. When I turn the rear A/C on the low side reads (48 psi) and high side (285 psi). Confirmed the A/C clutch was engaged during all testing. I did this a total of five times and each time the readings were the same (give or take a couple psi). I’m going to pick up a scan tool tomorrow as I currently don’t have one. I will post the codes after I test again. Thanks again for the help.

[Bubba2333]

I would have to take my vehicle back in to have it evacuated and recharged to find out home much refrigerant was added. I’m not sure what the mechanic added a couple weeks ago when the A/C was checked. Sticker under the hood says it should be 2.31 lbs.

[andrew vanis]

I would have to take my vehicle back in to have it evacuated and recharged to find out home much refrigerant was added. I’m not sure what the mechanic added a couple weeks ago when the A/C was checked. Sticker under the hood says it should be 2.31 lbs.

Does the mechanic have it in the record? Many charge you $ per OZ so maybe it's in your receipt.

However "adding" refrigerant without knowing total capacity can cause issues since it could be overfilled or still underfilled.

And some mechanics don't have a full understanding of the nuance of AC and just go with "just add some, more is better, right?" (And it's not, BTW)

When all info is not known, I like starting from a known "base" - system evacuated, pressure tested, vacuum tested,filled to specifications (if specifications exist otherwise full by performance) and then see how it performs.

Even this "base" may be hard to reach with a system that has been monkeyed with since it's impossible to know how much oil is in there without a full teardown and flush. With too much oil the specified refrigerant amount may result in a system that is overfilled in total oil+refrigerant capacity. Luckily most tinkerers don't mess with oil level - but some do. I was working on a friends truck which was messed with before me including adding oil. I didn't have time or interest then to flush it so while filling towards specified capacity I noticed Max performance was at about 75% of specified capacity and with more refrigerant performance went down (it was cooling worse/went temps started rising). Will not know what really is causing that and I'm guessing too much oil. We were getting down to 38F from the center vents with all doors open on a 105F day so we left it alone at that point.

[Tim]

Undercharging a system should not be done. It causes a lack of oil circulation and can cause reliability issues. The system must be fully charged, and then it must be determined why it is not performing well. Sometimes, it will take some trial and error, yet it is the correct way to repair a vehicle.

This is why "I' do care for those cans of refrigerant in a can with a green dial. There is a lack of proper information, but it sells like ice cream on a hot.

[tbirdtbird]

There may be a typo above, maybe means do not care for 12 oz cans with green dial.
Agree, tho, those should not be used, they are junk