2006 Trailblazer ac issues

[BrianF]

2006 TB short wheelbase, 270,000km, 4.2L without the auto climate control. Just manual temp control dual zone.

Back in May we found that the ac was not pumping cold. Electro-mechanical fan is engaging, took it for a drive to get airflow over the condenser with no change.

I found the ac compressor was not engaging. The clutch would not activate with key on, engine off or even engine running. I was not sure if the clutch died or seized.

While I have no gauges, there was pressure out the Schrader valve on the low pressure side. I bypassed the low pressure switch with a jumper with no change. The connector does have 5v reference.

The sole 10amp fuse is intact and I swapped relays with known working ones with no change. I then jumped the relay and the clutch engages and the pump runs and runs quiet.

So I am wonder where I can begin looking as to why the compressor is not being commanded on? Thanks!

 

[Chris142]

Bad clutch,relay,switch,evap temp sensor, ambient air temp sensor, bad dash switch....the list goes on and on. Need to do a lot more diagnostics.

 

[chemman]

Are there any DTCs present? Do you have a way to monitor various engine parameters with a decent code reader/live data scanner? Without knowing what data the ECM/PCM and BCM are getting and just as importantly what data they are not getting, it is extremely tough to diagnose the HVAC on your TrailBlazer.

Also, you'll need a set of HVAC gauges in order to know what the high and low side pressure are in the HVAC system.

Good Luck from another TrailBlazer owner.

 

[Falcon_LS]

You will definitely require gauges before you can do anything. Check the pressures first; if the high side if over 350 PSI or the low side is under 22 PSI, the compressor will not engage.

 

[wtd]

For whatever reason, the relay is not getting the command to pull the internal switch closed and operate the clutch. It could be because the pressures are not where they should be and the ECM more than likely is not sending the command to the relay or you could be missing a power or ground at the relay. You need to find out what your pressures are and get a wiring diagram to see where your inputs to the relay are coming from and test those.

 

[BrianF]

Thanks guys. Yeah, I have limited tools for data logging or diving deeper than a basic code reader. I will be looking at some ac pressure gauges, as I agree, there is some sort of input missing or off that won't allow power to be commanded.

 

[BrianF]

As I wait to source some pressure gauges, I did some more simple checks. The ambient air temp sensor appears to be working. It was mirroring ambient as I took it for a run out of the shop.

The low pressure side is what I focused on. The connector has 5v reference and good good ground. The LP switch is open, no continuity. That either means it's faulty or the system is low (gauges will confirm). So this is where I'll focus first. Bypassing the LP switch still does not allow the compressor to switch on. Perhaps there is another pressure parameter from either the high side or somewhere else that is tripped.