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Automatic Climate Control isn't controlling

Multiple issues from randomly not blowing to temp adjustments and more

Automatic Climate Control isn't controlling

Postby roosclan [OP] » Oct 21 2020, 5:42am

A couple years ago, I had an issue with my A/C in my '04 Z71 suddenly blowing hot on one side and cold on the other. Only turning off the truck and on again would fix it. I started to lose fan settings as well, so I replaced the blower motor resistor under the glove box (and did the wire harness splicing), and everything was wonderful.

Until this past August. I had a couple instances of the driver side suddenly blowing hot while the passenger side stayed cold, so I figured i would just order the resistor again when I got around to it. However, I have developed a different issue now: the blower will randomly decide to not work at all. I can be driving down the road with the blower at any speed and it suddenly stops blowing. It might come on again a few minutes later and do this off-and-on game for the rest of the drive. Last week, it quit completely for 3 days, then one day started working flawlessly again. On Sunday, I replaced the resistor and it worked for the rest of the day.

Monday afternoon, it was back to randomly stopping and starting, and the control panel itself is acting up. It quit completely this morning, and after I tried to cycle through the vent settings, the climate control module turned itself off even though I didn't hit the off button. I turned it back on, and still have no fan. I've dealt with difficulties adjusting the temperature knobs for a few years (turning the temp up makes it turn down unless I adjust one bump at a time s.l.o.w.l.y.) Now that it's fall, i don't need the A/C, so I don't know if it's randomly running one side cold and one side hot, but the other problems are more pressing since I need my defroster and can't rely on just air flow while moving to defog or defrost my windshield.

What should I be looking at now? If it's the automatic climate control module itself, how much of a pain is that to replace?
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Re: Automatic Climate Control isn't controlling

Postby nealinator » Oct 21 2020, 3:56pm

From your earlier problems with one sided temp fluctuations...that is pointing to the blend door actuators. When you have dual temp controls...you have one for each side. When they go bad...you get the temps on one side all messed up. These are very common to fail. Older ones like in your truck used to have a plastic gear break inside them. Later models like mine had some different failure modes...but both are very common.

For the blower issue...it may be a bad motor since you have already replaced the resistor.

And the dash module is another story...could be a bad connection behind there. Swapping them out is pretty simple if you go on ebay or somewhere and get an identical replacement. Those are far less common to fail and I would tackle the others first. Then mess with the module if it is still messing up.
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Re: Automatic Climate Control isn't controlling

Postby roosclan [OP] » Oct 22 2020, 2:34am

nealinator wrote:From your earlier problems with one sided temp fluctuations...that is pointing to the blend door actuators. When you have dual temp controls...you have one for each side. When they go bad...you get the temps on one side all messed up. These are very common to fail. Older ones like in your truck used to have a plastic gear break inside them. Later models like mine had some different failure modes...but both are very common.

What is confusing is that it stopped after I replaced the resistor two years ago, even though I never did anything with the actuators. It just started acting up again in August.

For the blower issue...it may be a bad motor since you have already replaced the resistor.

Would that account for the randomness of it working, not working, working again, etc.?
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Re: Automatic Climate Control isn't controlling

Postby nealinator » Oct 22 2020, 2:45am

Not sure...but some things will fail completely and all at once and other times it will be intermittent. Just depends on what is going wrong.

If itbis the same thing again, are you getting oem resistors or parts store aftermarket ones?
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Re: Automatic Climate Control isn't controlling

Postby roosclan [OP] » Oct 22 2020, 4:51am

nealinator wrote:Not sure...but some things will fail completely and all at once and other times it will be intermittent. Just depends on what is going wrong.

If itbis the same thing again, are you getting oem resistors or parts store aftermarket ones?

I got the resistor off of Amazon. It seems similar to ones I saw on rockauto.com
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Re: Automatic Climate Control isn't controlling

Postby nealinator » Oct 22 2020, 1:18pm

Went back and re-read your original post. I dont know how to diagnose the main control unit...so if it is an issue with that, you may just need to swap it out at a risk of throwing parts at it. For the blower cutting out....I would suggest a new blower motor. And it seems you still have at least one blend door actuator which needs to be replaced since you mention one side blowing hot when you want a/c.
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Re: Automatic Climate Control isn't controlling

Postby roosclan [OP] » Oct 23 2020, 5:29am

nealinator wrote:Went back and re-read your original post. I dont know how to diagnose the main control unit...so if it is an issue with that, you may just need to swap it out at a risk of throwing parts at it. For the blower cutting out....I would suggest a new blower motor. And it seems you still have at least one blend door actuator which needs to be replaced since you mention one side blowing hot when you want a/c.

I'll have to source a new blower motor fairly quickly, then, since the temps are getting colder and I'll need a defroster. The A/C blows cold most times, and would randomly start blowing hot on one side in the middle of a drive. It would be cold, then suddenly switch to hot for no reason, not just start that way and stay. It doesn't change from floor to panel or defrost, just suddenly change temps. I won't need to worry about it until next spring when it starts getting hot enough to use A/C again. Then I'll dig under the dash for the actuators.

I was hoping that all of this could be fixed with just replacing the main control unit. Then I saw the price... :shock: I think I'm glad the problems could be solved without the control unit.
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Re: Automatic Climate Control isn't controlling

Postby plant.one » Oct 23 2020, 6:19pm

have you checked that the temp sensor(s) in the cab isnt blocked?

i had to clean mine - there was a layer of dustbunny behind the grill that protects it.

its the little round grill peice up in the headliner

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from what you're describing it probably wont help, but it cant hurt to cover the basics, especially when they cost $FREE.99 to do :)
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Re: Automatic Climate Control isn't controlling

Postby roosclan [OP] » Oct 28 2020, 12:04pm

I don't use the Auto setting for temp control, but you're right. It can't hurt to clean it.
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Re: Automatic Climate Control isn't controlling

Postby roosclan [OP] » Nov 05 2020, 1:18am

Found the problem! The connector attaching the resistor to the motor is incredibly loose. Wiggling it caused the blower to come on or turn off. The blower works in all 5 speeds, so I will get the connector swapped out tomorrow after work.

As for the HVAC system shutting off completely at random and being very difficult to adjust temps... that will probably require a new control module which I hope to delay for a long time. I just dumped $700 into my son's N****n Altima.
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