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AC Compressor is not getting power

36010 Views 36 Replies 9 Participants Last post by  Onyxshard88, 
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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.
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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.
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Do you have a link to the factory service manual? I downloaded the Haynes manual and it was useless for this.
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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.
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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.
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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?
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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.
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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.
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I am sure that I had the right wire. And the resistance value did appear to be lined up with the temperature.
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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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