A/C blows cold up front but not in rear (1 Viewer)

[Deadmilenko]

Well I have look through most all of the forum topics and didn't see one that relates to my issue. So here it goes.

I have a 2000 LX470, front A/C blows cold however the rear ceiling vents do not, they blow slightly cooler air then air in the cab. Not really warm but not nearly as cold as the front vents. It doesn't matter whether the temp controls is switch to REAR on the front panel (meaning that the air is controlled up front) or if they are controlled by the rear controls in the ceiling behind the 2nd row and switched to cold temp, the rear air just doesn't get cold.

Thanks in advance for he help.

 

[Deadmilenko]

Here are the pics

Ceiling controls behind 2nd row

 

[blatant]

Are you giving it a couple or are you checking the air coolness at once. Mine takes a second or so to kick on and then another few to purge the hot air etc before even feeling cooler at the rear vents. If I checked right away, I would think it is NOT cooling... Maybe let it run for 5 minutes and then check again.

 

[Deadmilenko]

pretty sure I let it run for some time. I will go crank it up right now and check it in 5 mins

 

[Ming89FJ62]

it's very possible that the rear system has developed a leak. The refrigerant lines are aluminum and corrode over time. I had to have my welded shut and abandoned as the leaks were in unservicable locations. It doesn't affect the heat only the AC. You can use search for more details.

 

[flintknapper]

Are you giving it a couple or are you checking the air coolness at once. Mine takes a second or so to kick on and then another few to purge the hot air etc before even feeling cooler at the rear vents. If I checked right away, I would think it is NOT cooling... Maybe let it run for 5 minutes and then check again.

^^^^^^ Same for mine (99 LX470). I leave mine on maximum cool in the rear and just switch it on and off from the front. Typically, I get in the vehicle and crank up the front A/C, once underway, I open the rear vent windows (just briefly) to evacuate the hot air back there. Then switch on the Rear A/C. It takes a minute to kick in and start running.

In 4-5 minutes the vent temps back there will start to cool noticeably. It doesn't get as cool as the front and likely never will but it does cool things down pretty well. After the sun goes down...I definitely have to shut it off.

 

[Deadmilenko]

Yeah even after letting her run for 8 mins or so the air temp in the rear is cool, but not close to the cold temp up front.

 

[flintknapper]

Yeah even after letting her run for 8 mins or so the air temp in the rear is cool, but not close to the cold temp up front.

I've never taken a vent temp reading from the rear A/C but I will compare it to the front this weekend.

I would not expect it to match the front...owing to the location of the evaporator and vent ducting back there.

Both are subject to the dynamics of solar gain (with the large window areas back there) and heat transfer (conductive heat) from the roof and other body parts. It's not an A/C friendly set up back there.

Still...vent temps after 10 minutes of running should be reasonably cool. I would hazard a 'guess' that 20°-25°F. less than ambient would be pretty good for rear air.

Are you checking the temp at engine idle speed? If so...increase engine speed to 1200-1500 rpm and hold it for about 5 minutes then check it. See if it improves. If it does...we might assume the system is at least working back there, even if not optimal.

Lastly, I would put a set of gauges on the system and check your High and Low side pressures. Its quite possible your refrigerant charge is a bit low.

 

[Deadmilenko]

it's very possible that the rear system has developed a leak. The refrigerant lines are aluminum and corrode over time. I had to have my welded shut and abandoned as the leaks were in unservicable locations. It doesn't affect the heat only the AC. You can use search for more details.

hmmmmmmmmmmmmmm, if it was leaking wouldn't the coolant leak out completely making the AC unit not blow cold air anywhere?

 

[Deadmilenko]

Are you checking the temp at engine idle speed? If so...increase engine speed to 1200-1500 rpm and hold it for about 5 minutes then check it. See if it improves. If it does...we might assume the system is at least working back there, even if not optimal.

Lastly, I would put a set of gauges on the system and check your High and Low side pressures. Its quite possible your refrigerant charge is a bit low.

I will check it at a higher RPM next time I am on the road with it.

As for the High Low side pressure, is that something I can do or do I need to take if somewhere? Or can I just read the pressure from the gauge on a refill canister?

 

[flintknapper]

I will check it at a higher RPM next time I am on the road with it.

As for the High Low side pressure, is that something I can do or do I need to take if somewhere? Or can I just read the pressure from the gauge on a refill canister?

You can read the low side pressure from one of the available recharge canisters....BUT:

1. You don't know the accuracy of such a gauge.
2. Without high side readings you can't detect 'faults' in your system. The two readings together can be a good diagnostic tool to help determine the condition of your system. For instance...you could have a higher than normal high side reading and a diminishing low side reading (suggesting a restriction or blockage). Seeing the low or diminishing low side reading...the DIYer will naturally add more refrigerant (unaware the high side is getting even higher). You will actually make your cooling issue (lack of actually) worse this way.

The DIY recharge kits are not without their place and usefulness. IF your system simply has a slow leak, you catch it in time AND the rest of the system is otherwise in good working order....then the DIY recharge kits can be used to add refrigerant with good results. (slowly charge the system, note the gauge pressure AND monitor the vent temps).

IF you suspect there may be issues aside from a slow leak then you MUST use a manifold gauge set to correctly check/monitor the system.

 

[flintknapper]

Compared my Front and Rear A/C vent temps.

Conditions:

Ambient 92° F.
Vehicle started from cold engine. Idle speed throughout.
Both A/C units turned on at same time engine was started.
Both units had fans set to high speed and lowest temp selected.
Elapsed time until readings taken: 10 minutes.

Results:

Roughly 20°F. difference in front and rear vent temps. I am confident with more run time (as interior cools off) and greater engine speed (vehicle traveling), the rear temp would come down another 5-8° F.

 

[crimsonaudio]

hmmmmmmmmmmmmmm, if it was leaking wouldn't the coolant leak out completely making the AC unit not blow cold air anywhere?

Absolutely - happened to me, had to replace the rear lines - but we lost all AC when the leak occured.

 

[aljordan]

I am experiencing the exact same thing. The front will be cold enough to blow visible water vapor out of the vents if it's very humid. The rear doesn't get nearly as cold. I'd expect to see a 20F difference between the 2 vents as noted above.

 

[Deadmilenko]

Compared my front, mid and rear vent temps.

Conditions:

Ambient 80°F
Vehicle started from cold engine. Idle speed throughout.
Both A/C units turned on at same time engine was started.
Both units had fans set to high speed and lowest temp taken: 10 mins

Results:
Ambient 80°F
Front 44°F
Mid 58°F
Rear 62°F

A 14°F difference from front to mid, a 4°F difference from mid to rear, and a 22°F difference from front to rear.

 

[Deadmilenko]

sorry the pictures are so big the post was uploaded from my phone.

I now feel it is safe to say that there is not a leak and this drop in temp from the front A/C vent temp to the mid and then rear is standard with our LC and LX470's.

Thanks to all who helped in this topic.

 

[flintknapper]

sorry the pictures are so big the post was uploaded from my phone.

I now feel it is safe to say that there is not a leak and this drop in temp from the front A/C vent temp to the mid and then rear is standard with our LC and LX470's.

Thanks to all who helped in this topic.

It compares favorably to mine and I have no known issues with my A/C system.

Good of you to test yours and report back here. It might prove helpful to someone else.

 

[ibrahim83]

My understanding is the rear won't ever get as cold because they run along the roof and subjected to more heat than the main system.

 

[boofaz]

This happens with mine as well, I think the above comment is correct in that the tempurature of the roof has a huge impact in how cool the air gets that travels to the rear vents. When i park my truck in a covered or shaded spot the rear works much better then when parked in the sun. Still doesnt get as cool as the front but I just point the center vents towards the rear to help out till it cools down back there.