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AC Compressor is not getting power

36010 Views 36 Replies 9 Participants Last post by  Onyxshard88
2006 Frontier, 4.0 V6

I am getting no power to the AC compressor, so the clutch will not engage. I traced it upstream and am also getting no power at the pressure switch. But I do have power on both sides of the AC fuse. I have been unable to locate the AC relay and am wondering if this truck does not have one, at least not a separate one. Might this be IPMD related?

Any suggestions would be highly appreciated.
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Yes, the blower is working at all speeds, otherwise I suppose I would think about that flat resistor below the glove compartment.

I have had no luck locating an AC relay, though the Haynes manual wiring diagram does have one.
I think that they do. Where is the IDPM located in your 2011?

I saw a mention of a thermistor or thermal control assembly. But I thought that the thermistor was the resistor that controls the fan speeds.
Do you have a link to the factory service manual? I downloaded the Haynes manual and it was useless for this.
I have not found any FSMs for my truck that are not on a shady looking site. I am willing to pay for it, but not have my credit card data compromised.

But back to my problem: is it likely that I have a problem in my IPDM? I think that I have traced the problem back far enough to think that it's down to the component that decides whether or not to supply power to the pressure switch and compressor clutch.
Thanks very much. It would seem that the thermo amplifier that I keep hearing about is called the Intake Sensor in the FSM.

I suppose if that fails, the system will never send power to my compressor clutch magnet.
So is there a Thermal Control Amplifier on my 2006 Frontier? People have suggested this as a potential problem but everything that I have seen on it refers to a 1st generation Frontier. I can pull out the glovebox and open the evaporator box to see if there is one, but does anyone know if this is a wild goose chase on my 2006?
I am getting the impression that there is no Thermal Control Amplifier on a 2006 Frontier. The FSM talks about an Intake Sensor; does this perform a similar function on my 2006 that the TCA does on 1st generation Frontiers? Or am I strictly looking at an issue with the IPDM? I have not yet found anything in the FSM about the IPDM.
Quick recap: compressor is not getting power, pressure switch is not getting power, but the AC fuse is good. When I applied power directly from the battery to the compressor the clutch engaged. The 2006 engine has an intake sensor on top of the evaporator box. I got that out and ran the diagnostic tests from the FSM. I have continuity to and from the front air control connector to the intake sensor harness. I have roughly 5 volts on the sensor harness. This would suggest that I have a bad sensor. But one other data point: when I checked resistance on the old sensor itself, it appeared to be returning a resistance value reflecting the current temperature. I even warmed it up a little bit and the value dropped (there is a chart of resistance-to-temp in the FSM).

Should I just get the overpriced sensor or can anyone suggest some other diagnostic? It's getting hot in Georgia.
I am sure that I had the right wire. And the resistance value did appear to be lined up with the temperature.
None of the relays is marked as being the AC relay. I did swap the ECM relay for the low beam headlights relay and still had no AC.

I ran the auto self test (turn key on, press door switch 10 times, etc) and the magnetic clutch did engage 5 times. So it is capable of getting voltage there... this would suggest that my IPDM is okay, correct?

I went through some troubleshooting steps in the FSM. I have continuity between the front air control harness and the intake sensor. I also seem to be getting good resistance values from the intake sensor. Then as mentioned in MTC-70 (CHECK VOLTAGE FOR FRONT AIR CONTROL (A/C COMPRESSOR ON SIGNAL)) I performed another test, checking the voltage on terminal 10. This one seems odd... it wants me to test it with the A/C switch both on and off, but how does that work with the Front Air Control connector pulled out? The A/C light on the button does not change when I toggle that A/C switch. The FSM (MTC-70) says that I should have 0 volts with the A/C switch on and "battery" voltage with the switch off, but I had a little over 7 volts in both cases, so I am not sure if it is "OK", "NG-1" or "NG-2".

Any advice? This is about the most difficult troubleshooting and auto repair I have ever done. And it's in the 90s in Georgia now.
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