08 Tahoe Rear AC not blowing cold

[Dustin Jackson]

Hello guys, I have the temp controlled AC for the front and rear but I realized that the rear is just blowing warm air unless I turn on the heater then it blows hot air, but ever AC.

After doing some research I checked to see if the rear AC lines are getting cold after running the truck AC for a while and I found that the AC lines going to the rear of the Tahoe do not get cold at all.

What does this mean?

Is this is symptom of the expansion valve or orifice tube getting clogged? Or is this an indicator that the rear AC lines have been cut from the AC system?

I will be crawling under the truck this weekend to make sure that the AC lines look ok.

Any insight into how this system works would be greatly appreciated.

 

[Jolly Roger]

If Im not mistaken, the AC lines run under the pass side step bar and are notorious for corroding and leaking. Id start there.

 

[Dustin Jackson]

If Im not mistaken, the AC lines run under the pass side step bar and are notorious for corroding and leaking. Id start there.

@Jolly Roger If there was a leak wouldn't the AC for the front stop working also? Are the lines connected between front and rear? When I do my brakes I am going to inspect the AC lines but I just don't know enough about how the system works yet to properly diagnose it.

 

[swathdiver]

Hello guys, I have the temp controlled AC for the front and rear but I realized that the rear is just blowing warm air unless I turn on the heater then it blows hot air, but ever AC.

After doing some research I checked to see if the rear AC lines are getting cold after running the truck AC for a while and I found that the AC lines going to the rear of the Tahoe do not get cold at all.

What does this mean?

Is this is symptom of the expansion valve or orifice tube getting clogged? Or is this an indicator that the rear AC lines have been cut from the AC system?

I will be crawling under the truck this weekend to make sure that the AC lines look ok.

Any insight into how this system works would be greatly appreciated.

There are two actuators back there that need checking with a scan tool.

 

[Dustin Jackson]

There are two actuators back there that need checking with a scan tool.

@swathdiver I understand that actuator moves the blender door for the rear, my problem is that the cold does not make it to the rear AC system. The rear AC lines never get cold. Am misunderstanding what an actuator is?

 

[swathdiver]

@swathdiver I understand that actuator moves the blender door for the rear, my problem is that the cold does not make it to the rear AC system. The rear AC lines never get cold. Am misunderstanding what an actuator is?

No, I don't think so. The actuators control the modes and temperature but I think the lines should be cold. @91RS @Scottydoggs

 

[Dustin Jackson]

No, I don't think so. The actuators control the modes and temperature but I think the lines should be cold. @91RS @Scottydoggs

@swathdiver I tested the Rear AC and I can switch between HOT and luke warm (supposed to be cold) and switch between top and bottom vents so I am confident the blend doors all work but the lines definitely do not get cold.

My next step is to verify that the AC lines are intact and haven't been spliced off by a previous owner, if everything looks OK I was going to replace the rear expansion valve and Orifice tube and recharge it from there. Any additional input would be great, thanks for the help.

 

[swathdiver]

@swathdiver I tested the Rear AC and I can switch between HOT and luke warm (supposed to be cold) and switch between top and bottom vents so I am confident the blend doors all work but the lines definitely do not get cold.

My next step is to verify that the AC lines are intact and haven't been spliced off by a previous owner, if everything looks OK I was going to replace the rear expansion valve and Orifice tube and recharge it from there. Any additional input would be great, thanks for the help.

Called in the guys who know more about AC systems than I do, which is not much! Do you have a subscription to AllDataDIY for the shop manual and troubleshooting guide?

 

[Doubeleive]

@swathdiver I tested the Rear AC and I can switch between HOT and luke warm (supposed to be cold) and switch between top and bottom vents so I am confident the blend doors all work but the lines definitely do not get cold.

My next step is to verify that the AC lines are intact and haven't been spliced off by a previous owner, if everything looks OK I was going to replace the rear expansion valve and Orifice tube and recharge it from there. Any additional input would be great, thanks for the help.

so did you remove the rear passenger side kick panel and visually watch the actuator? or did you simply adjust the controls?
the rear ac lines will not be very cold at all one will be warm and one will be very slightly cool, they are the metal lines
best thing to do is to simply pull the panels off in the back and look at the actuator to see if it is really moving or not, the one closest to the blower motor is the one that controls hot/cold
the center portion has a hole and notch in it, the notch should move all the way forward/backward to the corresponding marks on the outer casing, see attached photo for reference

 

[91RS]

If you're front A/C is working then the rear A/C should as well because the lines are all connected to the same system and the refrigerant flows whether the rear HVAC is on or not. It is possible someone bypassed the rear system for whatever reason so make sure the lines are actually connected to something under the hood. They're not super common to leak in the south but they are really expensive to replace so I could see someone just buying two pickup truck A/C hoses and bypassing the rear A/C if they didn't want to fix it.

Either way, you more than likely have an actuator problem. I just replaced one in a friend's 14 he just bought. You can check for codes with a scan tool and command the actuators and see if they're doing what they're supposed to. If you have a short wheel base, the actuators will be on the inside of the case against the body so you will have to unbolt the case from the body and slightly roll it to get to the actuators (you don't have to disconnect the A/C or heater hoses to do this).

 

[Dustin Jackson]

If you're front A/C is working then the rear A/C should as well because the lines are all connected to the same system and the refrigerant flows whether the rear HVAC is on or not. It is possible someone bypassed the rear system for whatever reason so make sure the lines are actually connected to something under the hood. They're not super common to leak in the south but they are really expensive to replace so I could see someone just buying two pickup truck A/C hoses and bypassing the rear A/C if they didn't want to fix it.

Either way, you more than likely have an actuator problem. I just replaced one in a friend's 14 he just bought. You can check for codes with a scan tool and command the actuators and see if they're doing what they're supposed to. If you have a short wheel base, the actuators will be on the inside of the case against the body so you will have to unbolt the case from the body and slightly roll it to get to the actuators (you don't have to disconnect the A/C or heater hoses to do this).

@91RS @Doubeleive @swathdiver Thank you for the input gentlemen, I will inspect the rear actuator before proceeding. I first need to address my battery cables, I have to shake and jiggle my negative battery cable to get my truck to start which resets all the electronics in the truck. I wonder if there is a slight chance this battery cable situation is contributing to my rear AC not working right.

 

[Doubeleive]

@91RS @Doubeleive @swathdiver Thank you for the input gentlemen, I will inspect the rear actuator before proceeding. I first need to address my battery cables, I have to shake and jiggle my negative battery cable to get my truck to start which resets all the electronics in the truck. I wonder if there is a slight chance this battery cable situation is contributing to my rear AC not working right.

it's unlikely because the system would reset if power is lost, but.....with these trucks power issues can make all kinds of weird stuff happen.

 

[91RS]

A battery cable can absolutely cause issues with the HVAC. I’ve seen it more than once.

 

[iamdub]

@swathdiver I tested the Rear AC and I can switch between HOT and luke warm (supposed to be cold) and switch between top and bottom vents so I am confident the blend doors all work but the lines definitely do not get cold.

My next step is to verify that the AC lines are intact and haven't been spliced off by a previous owner, if everything looks OK I was going to replace the rear expansion valve and Orifice tube and recharge it from there. Any additional input would be great, thanks for the help.

You ever resolve this? My refrigerant lines stay at ambient temps but my front AC works fine. It's like the aluminum lines to the rear evaporator have a shutoff valve.

 

[Doubeleive]

You ever resolve this? My refrigerant lines stay at ambient temps but my front AC works fine. It's like the aluminum lines to the rear evaporator have a shutoff valve.

have you pulled the rear passenger panel off and looked inside to see if the acturator is working?

 

[iamdub]

have you pulled the rear passenger panel off and looked inside to see if the acturator is working?

Haven't been home enough to mess with that. I've only copped a quick feel while laying on the driveway in passing. I can't spend much time there due to the heavy exhaust fumes.

But, it switches from hot to cold (or what should be cold) in accordance with the control panel. If I put it at 90°, the vent temps get hot. If I put it at 60°, they change to cooler air. I'm sure if the evaporator was actually being cooled, then that air would be chilly as if it were trying to get it to 60°. Regardless of actuator movement, the evaporator isn't cool. I was advised in another thread that the expansion valve might be stuck and to knock on it with a hammer. Whatcha think?

 

[Dustin Jackson]

@iamdub No I have not gotten around to fixing this yet. The front AC does an excellent job of providing enough cooling for now. I agree with you, when the rear system is set to 90 it is hot, when I set it to 60 it is luke warm. I assume that the rear blend door is not working all the way. It has been a while since I felt the rear AC lines to see if 1 gets cold or not, I assume 1 line would if the refrigerant is flowing to the back of the tahoe properly.

 

[Doubeleive]

Haven't been home enough to mess with that. I've only copped a quick feel while laying on the driveway in passing. I can't spend much time there due to the heavy exhaust fumes.

But, it switches from hot to cold (or what should be cold) in accordance with the control panel. If I put it at 90°, the vent temps get hot. If I put it at 60°, they change to cooler air. I'm sure if the evaporator was actually being cooled, then that air would be chilly as if it were trying to get it to 60°. Regardless of actuator movement, the evaporator isn't cool. I was advised in another thread that the expansion valve might be stuck and to knock on it with a hammer. Whatcha think?

I think you should take the rear hvac cover off and visually watch the actuator blend door first to verify it is moving to full cold, you can see the markers on the center gear move. It has 3 marks, visually watch it going to hot/middle/cold, if it is stuck you will see, the rear never gets as cold as the front in any case. It will be the 1st acutator closest to the blower motor, the 2nd one up farther where the vent splits up/down and does not have any affect on temperature.

 

[iamdub]

@iamdub No I have not gotten around to fixing this yet. The front AC does an excellent job of providing enough cooling for now. I agree with you, when the rear system is set to 90 it is hot, when I set it to 60 it is luke warm. I assume that the rear blend door is not working all the way. It has been a while since I felt the rear AC lines to see if 1 gets cold or not, I assume 1 line would if the refrigerant is flowing to the back of the tahoe properly.

The larger line should be cold and sweating. After reading the suggestion that the valve might be stuck, I'm thinking this could be a possibility resulting from lack of use. My Tahoe sits a lot.

 

[iamdub]

I think you should take the rear hvac cover off and visually watch the actuator blend door first to verify it is moving to full cold, you can see the markers on the center gear move. It has 3 marks, visually watch it going to hot/middle/cold, if it is stuck you will see, the rear never gets as cold as the front in any case. It will be the 1st acutator closest to the blower motor, the 2nd one up farther where the vent splits up/down and does not have any affect on temperature.

What does that second one do- floor or overhead vents?

I wanna tear into that to inspect and clean it. Even if I fix it elsewhere, air flow is a critical factor.