Squeaks Defrost Only Problem
Of course this kind of stuff never happens when it is moderately cool out, but rather when the temps are constantly over 100 degrees. Squeaks, our 2000 Jeep Grand Cherokee WJ, decided to only blow air out the defrost vents earlier this week. Controls would not do anything. While the AC was still blowing, when it is 105 out, not having that airflow across your body makes it seem a lot hotter in the vehicle.
There are a couple of failure modes for defrost only. Typically it is due to a vacuum leak in the engine bay somewhere, and the system can’t make enough vacuum to change the door settings on the HVAC (vacuum controlled). With no vacuum to the HVAC system, it will default to the defrost setting. A lot of times when this happens, your cruise control will also fail as it is vacuum assisted as well. This threw me off a little, as the cruise was still working just fine. I figured we had a problem with the actuator under the dash. First though, I decided to check the lines. Search the firewall area, intake manifold area, and as a last resort, pull the passenger headlight out as there is a line behind there that will split. I was lucky enough to find a really small line on the passenger side firewall that was broken. Must have been a small enough line to keep the HVAC door in defrost, but not big enough of a leak to affect the idle or cruise control.
A quick splice with a rubber section of vacuum line, and we were back in business. Since it is in the garage, I’ll rotate the tires before sending her back out the door.