Ac partially not working

[BrianF]

Alright, I think I never had an actual post on this, although I made mention in another thread.

On my 2006 TB, non auto climate control model. Ac clutch not engaging when button pushed on.

Jumped my low pressure switch, no change. There was some pressure out the Schrader valve, for what that's worth. There is the 5v reference signal on the connector.

All fuses intact. Swapped relays and all work but no change.

So today, I decided to go back and work on it again, seeing as I have a bit of time now. I jumped the relay and voila, the clutch engages.

So, the clutch works, the pump works (no grinding noises), now I have to figure out what is causing the relay to not be triggered.

Any thoughts?

 

[TJBaker57]

There are a lot of possibilities. First thing to know is that no switch or sensor or any other type device "turns on" the clutch. The HVAC module "requests" the clutch but it is the PCM that checks a half dozen or more parameters before either turning on the clutch or refusing.

You say there is some pressure at the low pressure cycle switch. Just how much pressure is there?

 

[BrianF]

While I have no gages, there is some pressure. I tripped the Schrader valve and there was some refrigerant that came out.

The compressor does not engage at all, whether start up or if signaled while engine running. It will only engage when I jump the relay.

 

[Mooseman]

So you jumped the low.pressure switch and no compressor. It's not happy with something else. Only two other things come to mind. The high pressure switch and the ambient temp sensor. Ambient comes into play if it thinks it's below freezing.

 

[mrrsm]

Ordinarily, the A/C Compressor Disconnect will *Kick-In* courtesy the Low Pressure A/C Switch when the Pressure drops below 40 PSI at Sea Level. The Scroll Compressor needs the protection of having enough Refrigerant in the System in order to carry-suspend the 6-8 Ounces of PAG 46 needed throughout the Compressor Internals and Lines and thus... avoid damaging it while accidentally "Running It DRY". So By-Passing that Safety Feature by Jumping the LP A/C Switch Harness Plug should be avoided if possible.

Besides applying the "Blue Nylog" Sealant to the internal Green "O" Ring on the Replaceable Low Pressure A/C Port Sensor using a Brand New Schrader Valve... jik ... the Low Pressure Sensor is the actual point position of the Refrigerant Loss... it IS possible to replace that errant Leaking Schrader Valve too... W/O the Need to Evacuate any further Refrigerant... using THIS Kit:

Blue Nylog:

https://www.amazon.com/dp/B008HOSQQQ/?tag=gmtnation-20

Live Schrader Valve R&R Kit

Note: This Kit Does NOT get used on the Standard High (Red) and Low (Blue) Service Ports... there is a Separate, Distinct Automotive A/C Quick-Disconnect Schrader R&R Kit for that purpose on Amazon:

https://www.amazon.com/dp/B09PHG4PF8/?tag=gmtnation-20

 

[Mooseman]

Like he said, low system pressure is not the issue as he jumped the low pressure switch.

Here's the schematic for the A/C. I'd be checking:

Ground wire at the low pressure switch and continuity to HVAC module
Relay connectors for proper power, ground and signal from PCM
Wiring from the high pressure sensor to PCM
Serial data wire continuity from HVAC module to the splice pack as that is the A/C request line (we'll assume it's good from splice pack to PCM since nothing else is not working)

And if you have live data logging capability (Maybe @TJBaker57 can help with this):

Ambient and/or intake temp sensor
Coolant temp sensor
A/C request status
High pressure sensor
Low pressure switch status (with connector jumped and not)

 

[budwich]

While I have no gages, there is some pressure. I tripped the Schrader valve and there was some refrigerant that came out.

The compressor does not engage at all, whether start up or if signaled while engine running. It will only engage when I jump the relay.

As tjbaker57 suggested, "lots' goes into causing "compressor run".... most of which require a set of gages as a minimum and perhaps a DMM. Further, forcing compressor on for any periods of time without knowing the "gas status" of the system is likely asking for a larger repair bill.... "spitting out" a bit of gas out of a connector ain't a very good test.

I don't think just shorting out the "low pressure switch" in this particular system will actually confirm anything as that electrical condition does not have any direct connection to the AC clutch (like some other / old systems). In this case, the system also has access to a pressure measuring sensor which will be the "main control" for the system. IF its indicating a low pressure, the low pressure system will at best just confirm it. Actually what you should do is a resistance check of the low pressure switch.... IF its open, then you have likely have low pressure.

 

[BrianF]

Thanks guys. I do not have data logging or anything that can do a deeper dive than a basic code reader. I'll start digging on that list and see what I can get done with basic tools. I got to look at those ac pressure gauges as well.

 

[BrianF]

I did a visual check of the ambient temp sensor and the readout on the mirror was accurate to what ambient was. I rolled the vehicle out into the sun and the temp did increase realistically.

Yesterday I tried a resistance and continuity check of the low pressure switch and had nothing. So even after bypassing, I wonder if there is in fact another sensor. @budwich I agree, spitting out is far from any accurate reading, rather it shows the system has more pressure than atmospheric.

I am looking for some gauges locally but of course being a Sunday, that makes things a bit tough.

@Mooseman, thanks for the schematics!

@mrrsm thanks for your information, I jumped the relay to double check that the clutch was not dead or seized and ensure power to it. I was not looking forward to ripping it apart.

 

[TJBaker57]

Yesterday I tried a resistance and continuity check of the low pressure switch and had nothing

Disconnect the harness at the low pressure cycle switch and with the key on test for about a 5 volt signal voltage at the harness connector. The dark blue wire should show 5 volts or close to it. The black wire should show continuity to ground.

 

[BrianF]

@TJBaker57, thanks. Yes there is a 5v reference signal. What I will do is test for ground.

 

[TJBaker57]

@TJBaker57, thanks. Yes there is a 5v reference signal. What I will do is test for ground.

If you have a good ground and the 5v signal then test for continuity through the switch. If there is no continuity through the switch then either you do not have enough refrigerant pressure or the switch has failed.

For reference sake if the outside temperature is say 80°F and the compressor is not running there should be about 87 psi in the system. High and low sides will be equal. The pressure is then a direct result of the temperature.

 

[BrianF]

I checked ground on the LP switch and I have what I would say is good. It's very low resistance. I too am led to believe that either the switch is bad or it's low on refrigerant. This is a problem but bypassing the switch does not kick the compressor on. So it's possible low refrigerant also effects the high pressure side and or there is another reference the system uses.

 

[Mooseman]

Jumping the low pressure switch takes the refrigerant level out of the equation. There no other reference for a low refrigerant level. The high pressure sensor only gives high pressure reference. Something else is going on.

 

[BrianF]

OK so only those two references on pressure. In any event, I am either low on refrigerant and or my LP switch is inoperable as I do not have continuity through it.

 

[TJBaker57]

This is a problem but bypassing the switch does not kick the compressor on.

If you bypassed the switch by connecting together the two wires from the harness, or by grounding the 5 volt signal, amd the compressor still did not run then there is or are additional reasons the clutch is not being commanded on.

The PCM checks several parameters before engaging the clutch. I have read that even an unsteady idle will cause the PCM to not engage the clutch.

 

[TJBaker57]

Here are some of the reasons for no AC clutch engagement....

 

[Mooseman]

Another possibility is a broken trace in the fuse box. That's why you have to check each connector at the relay. We know two are working OK, the 12V+ and the one going to the compressor. Then there's the other 12V+ and the ground signal from the PCM. For the last one, if not getting the ground signal from the PCM, then you have to check continuity on that wire from the relay to the PCM.

What about the HVAC module? Everything working there? Blower fan and actuators working?

Beyond the basic stuff, it may be difficult to diagnose without a scan tool.

 

[c good]

Mine had too much air gap. The electromagnet didn't have enough strength to pull the clutch plate into lockup.

It would work intermittently. Eventually solved the problem with a new compressor. Only later did I find out I could have removed a shim, thereby reducing the air gap.

You can test it by carefully taking a broom handle and pushing on the front of the clutch plate to see if it helps it lock up.

 

[Nashcat]

My 2008 TB A/C wouldn’t kick on due to low engine temperature. The tech said a bad thermostat that doesn’t get the engine up to temp quick enough, makes it think it doesn’t have any water in the block, thus shutting down compressor. A fault reset would let it run once. A new engine thermostat fixed it. It’s been fine for 6 years.