This 2005 Ford Escape came in with the complaint that the air flow stopped coming out the vents sometimes. The owner said he did not feel it coming out anywhere else either but he also had not checked real well either. I inspected the vacuum hoses, check valve and reservoir under the hood and found no problems. Normally the airflow will shift to the defrost if there is a vacuum problem. I test drove the vehicle a couple of different times and on the last test drive the problem occurred. The air flow was very reduced and it was not coming out of any other vents. Pretty sure I know what’s going on now. I lifted the hood and saw a significant frost build up on the a/c lines.
The compressor was engaged and the engine was running during this test. The reduced air flow was being caused by the same frost buildup on the evaporator core. Effectively turning it into a block of ice that air could not pass through. I disconnected the clutch cycling switch and the compressor immediately disengaged.
I left the switch disconnected and allowed the engine to continue to run.
Slowly the frost melted…
…and the airflow was restored. I installed a new clutch cycling switch and test drove again to complete the repair.
Had the compressor stayed engaged after the switch was disconnected I would have looked further to see if the relay was sticking or if there was a mechanical clearance issue at the compressor clutch. One last note about this repair. I did notice that the compressor and the accumulator had recently been replaced. This faulty switch could have easily lead to the original compressor failure and certainly would have caused the replacement compressor to fail if I had not found the issue.