This 2008 Chevrolet Impala came in with the complaint that the blower speed would shift up and down. This was also accompanied by a drastic change in the air conditioning vent temperatures. This was actually quite easy to figure out while sitting in the driver’s seat. I have the luxury of having a Tech 2 scan tool and could look at the a/c high side pressure readings. When the problem would occur the head pressure was in excess of 400 psi.
While working the a/c and recirculation LEDs were on.
When the problem occurred the a/c and recirculation LEDs would go out and the fresh air LED would come on. There would seem to be a change in blower speed but it was actually just the fresh air/recirculation door changing positions. The compressor would also turn off.
The same high pressure could be seen on the gauges in my a/c machine.
I recovered the refrigerant from the system.
The level in my machine increased by two pounds of refrigerant after the system was empty.
This Impala has a 3500 V6 engine.
The label clearly states 1.4 pounds of refrigerant for this system.
The system was back working with the correct refrigerant charge installed. I did notice the high side pressure was slightly high at 275 psi and found that the right or passenger side cooling fan was not on.
Someone had already replaced the Fan 3 relay with an inexpensive replacement. I performed some bidirectional tests on the relays with my Tech 2 scan tool and found that all three relays would click and that both fans would work on low speed, when the fan 1 relay was energized.
I keep the relays in stock so I replaced the cheap replacement relay with a genuine ACDelco relay and the problem was corrected.
The pressures are now good and the vent temperature is in the mid forties.
Another one fixed.
While I do my best to detail as much information as possible. There are many repairs that I have yet to document and some of you may wish to have more than I have provided. I would strongly recommend subscribing to one or both of the following data companies for further assistance. Although having an abundance of information does not guarantee an easy repair, the lack of adequate information will guarantee a failed repair!
Need more information? Subscribe to Mitchell1 today!