Dual Zone Climate Control Problems

DaveEd · May 9, 2005

I recently purchased a 2003 Yukon SLT and am having problems with the electronic dual zone climate control. Unfortunately, it is now out of warranty with 62,000 miles. Regardless of what temperature I have it set, in the “Auto” mode the fan stays on the highest setting and only blows very cold air. Even on a long trip, the fan speed does not go down from the highest and occasionally the second highest speed setting and the air stays real cold. The only way to get heat is to set the temperature all the way up to 90 degrees and then some warm air comes out, but again the fan stays on high speed. The only way for me to moderate the temperature is to manually set the fan speed and turn the ac button on/off, or the whole unit on/off. Thankfully, I have heated seats for warmth!!! I have not checked if the rear seat climate control is working or not. I spent all my money on the truck, so would like to fix it myself, if possible. I am assuming that the problem is with the dash control unit or the actuator that controls the mixing doors or the temperature sensor(s). I would greatly appreciate any guidance on diagnosing and fixing this problem. Thanks in advance for the help!

GM-Tech · May 9, 2005

Without some diagnostic info, it's difficult to say for sure, but we do replace a control head here and there.

DaveEd · May 17, 2005

I replaced the electronic climate control head unit, but it did not fix the problem. I removed the access cover to the mixing door actuator by the center hump and watched it as I turned the temperature all the way hot (the only way to get any warm air). The exposed metal piece only moved ¼ of a rotation at most. Is the actuator motor likely the problem? Are there any other items that I should check, such as the overhead temperature sensor and if so what should I look for? Any advice would be appreciated. Thanks!

GM-Tech · May 17, 2005

Lets remember that there are two temp actuators since it is a dual zone system. If both sides are equal in temperature no matter what, it's unlikely both actuators failed at the same time.

If you are in "auto" mode and no heat is available to warm the interior and you have it set to heat, it would be natural for the blower to stay on high. The system is trying to warm up the interior as quickly as possible but it ain't happenin' and it won't slow down until it does. The question is, can you control blower speed if you're not in auto?

I suspect you may have a problem with getting hot water through the heater core. Can you go out and feel both heater hoses that go into the case? When warmed up, they should both be so hot you can't hold 'em.

DaveEd · May 18, 2005

Thanks for getting back to me so quickly, I do appreciate it. To answer your question, yes I can control the fan speed manually. As originally mentioned, the fan stays on high when in “Auto” blowing only cold air, so I moderate the temperature by turning the AC button or the whole unit on/off and I set the fan at a lower speed. I get your point about the blowers staying on high until the desired temperature is reached and I will check the hoses for heat (can you please generally indicate which hoses/where I am checking?). That said, the blower remains on high even when cooling the vehicle to where I am certain it has reached and passed the desired temperature; it simply does not moderate itself either way in heat or cool.

Good point about the small likelihood of both actuators failing at the same time, however I bought this truck used and have had this problem the entire time, so I can’t confirm the actuators failure, but I can tell you that it is a problem on both the driver and passenger side (I confirmed today by adjusting the passenger side to a separate temperature; same result, cold air only with blower on high, until turning to the maximum heat setting which produces some heat). I also checked the rear system, which seems to be working fine; I set a temperature and the blower and air temp adjust accordingly. If it is both actuators, is it true that I will not be able to do the passenger side work myself because of the difficulty in accessing the passenger actuator? Again, I appreciate your help, as I really cannot afford to pay the dealer $150 just to diagnose the problem, especially if I will need to buy parts (and labor?) as well. Thanks!

GM-Tech · May 18, 2005

The heater hoses would be on the passenger side at the rear of the engine, going into the bulkhead (firewall).

Keep in mind that with auto air systems, if you set the temp to 60 or 90, you are requesting max cool or max heat and overriding the automatic control of temperature. In order for the auto air to control things, the temp must be set to no lower than 61 degrees or no higher than 89 degrees.

The rear system is separate and heat back there, for example, would not be affected if the front heater core is plugged.