2007 – Yukon Denali – Automatic AC – No Airflow – Sometimes

[Dan_G]

I have a 2007 Yukon Denali. The automatic climate controls usually work. Every so often I get no airflow. Yesterday I was on a drive for about 3 hours. There was no airflow coming out of the vents.

I tried everything I could to get some air movement from any of the vents - no go. I manually cranked the fan speed to max. I can hear the fan speed ramping up and roaring away. The fan makes plenty of "fan" noise – but that's all it does – it certainly does not move any air.

I turned off the HVAC and turned it back on – no change. I switched back and forth between recirculated air and outside air – no change. I selected each vent mode – defroster, floor and dash vents – no airflow. Switched "Aux" on and off. Cranked the temp up to 90 - no change. Switched into dual mode and dialed up the temp on the passenger side - no change. I even opened the windows a bit and drove for a while – no change. I got no airflow no matter what I selected (or as close to zero as possible). I even turned off the car at a rest stop and came back and fired it up – no change, no airflow.

The fan was running fine but I felt no airflow at all, So I have no idea of where the all the air was going. I was lucky, it was in the 50s so I did not really need any heat.

Today fired up the truck and … it’s fine. It switches between all the vents, moves plenty of air. It’s totally 100% fine. I did nothing different. I started the truck and the climate controls are now perfectly fine. It has done this once before in the summer. So same problem but in AC more. The problem disappeared the next day. So I know there is something odd going on. I’m not sure what to do. Perhaps I'll just have to wait for it to fail completely. The fan definitely works. You can hear it roaring when you turn it up. It’s behaving like something is blocking the ductwork right after the fan - but only sometimes. Anyone have issues like this?

 

[m.mcmillen]

You could be a little low on refrigerant and the evaporator is freezing up. When it does that, air won’t flow.

 

[Mooseman]

As per @m.mcmillen , pull the A/C clutch relay and see if the problem disappears. This would confirm it.

 

[Dan_G]

Ok, that makes sense. It's winter so I don't really need the AC - although the defroster almost certainly uses the compressor. It sounds like low refrigerant could indeed be the problem. I have some gauges so I'll pop them on there - see how low that evaporator temp really is. It did run low on refrigerant in the summer and I charged it back up. I'm going to need to need to find that leak anyway.

 

[Dan_G]

You folks are great. I can confirm that's the problem. It's very low on refrigerant. The evaporator coil obviously froze and blocked the airflow. I was not sure how they ducted the thing but it's pretty clear all the air from the fan goes over the evaporator coil all the time. The gauges show it's running at basically 0 psi refrigerant pressure on the low side with the compressor running. It will definitely freeze at that pressure - coil temp would be about 14 below zero. If I turn off the compressor, the low side refrigerant pressure rises to like 20 or 30 psi. I'll yank the relay for now. I need to find that leak. I have a vacuum pump and some 134a cans but no sense charging it until I find the leak.