A/C compressor does not kick on

Hello, when a temperature sensor reads -40 degrees it means that the sensor has an open wire inside of it or a wire going to the sensor is open (broken). The -40 degrees is a default strategy the cars computer reverts to. Here is 2 wiring diagrams of the A/C wiring, there isn't much involved. Just the relay you already checked and the wiring the computer. There should be a code stored in the computer for the ambient temperature sensor. So you need to have the computer scanned for codes to start with, your local parts store will scan it for free. You should check Fuse #59 it feeds the A/C compressor relay. You can also check at the compressor for power on the light blue wire with the system on. The relay is directly controlled by the cars computer. It sounds like because the computer is seeing -40 degrees outside, its probably not turning the A/C compressor on. But i would address the temp sensor first, then see if your compressor turns on. Has the check engine light been on at all?

Check engine nd vtm-4 lights on for o2 sensor.. the wire to the ambient sensor is broken, so what am asking is if this ambient sensor is broken and not giving the right temperature it could stop the A/C compressor from coming on? Is there a way to test it such as in connecting the two wires of the sensors together?

Test light shows ground on the yellowish wire but no power or ground on the brown one. I tried connecting the ground to the sensor and then straight 12v power and nothing happened.

Yes you can reconnect the 2 wires as long as they're the same color, just so you don't attach the wrong wires together. Are you getting codes for the 02 sensor as well?

The end of the wires to the ambient sensor are too short to connect them so i attached couple of clips and compressor didn't come on and temperature didn't change from -40. One has ground and the other has nothing. Yes, also an o2 sensor p2237. And vtm-4 light as well which i think gave me a speed sensor for one of the wheels. So how do i know that this sensor for ambient temperature can be the cause? I very doubt it will not let my A/C compressor come on.

okay, so we have to figure out which temperature sensor has the broken wire. there's an outside temperature sensor and an Evaporator temperature sensors. One has a brown wire and the other is brown/white. The yellow and green wire is ground for both sensors. If the Evap temperature sensor wire (brown) is broken it will not allow the compressor to come on.

It is located on the front of the evaporator mounted to the plastic grille. Two wires, must be the outside temperature sensor cause of the colors. The evaporator wires are similar but they end up being black coming out of the sensor as am seeing in the diagram, which isn't the case here.

Just go by if it's a brown wire or if it's a brown with a white strip, it's located behind the front bumper. The outside temperature sensor is like any other thermistor, same as a coolant sensor, intake air temperature sensor. It receives a 5 volt reference and the ECM monitors the voltage on the circuit to make calculations. Never apply 12 volts to it. You may have damaged the sensing circuit in the climate control unit.

Brown/white, yellow/green.

Here.

There may be other damaged wires too, depending on how that one got broken. I would follow that wire as far as you can and make sure there's no other damage. Here's the rear A/F sensor (02) Bank 1 Sensor 1. Check the wiring for this as well before replacing the sensor.

before catalytic right?

Yes, the A/F sensors are wide band 02 sensors and are before the catalytic converter, the 02 sensors after the cat are narrow band regular 02 sensors. Here's a diagram of the climate control unit if you want to check the brown/white wire coming straight out of it. Should have a 5 volt reference coming out. You may want to go through your fuses too, just to verify they're all okay. That broken wire hanging down could have shorted out on the frame. Check this #3 7.5amp Fuse as well, it powers up the climate control unit and panel.

No the were not hanging i cut them, they were just broken and insulated.

Fuse checked it more than once, all fuses have power and good. The A/C display is fully functional. And none of the wires behind it are brown/white.

The climate control unit is different than the display panel with controls on it. The Climate control unit takes commands/inputs from the display panel. Here is its location:

found it. checked volts and it's 5v as you mentioned. also checked on the front sensor wires by attaching + and - via multi-meter to the 2 wires and also gave me 5 volts.

That's good, check the sensor unplugged for resistance on the meters ohm setting to make sure the sensor isn't open inside. Can I ask why you cut the wires to begin with? Just curious. As for your A/C problem turn the A/C on and check the wire at the compressor for power.the light blue wire.

Resistance on the sensor is none, which i believe means it bad. The sensor harness wires were cut from the root of the clip so i had no way of connecting back.

Your meter is reading OL? If so definitely a bad sensor. Open windings inside. Need to replace that.

Yes, not getting any change in readings on ohmeter. Ordered another, hopefully will solve it. Read that others had similar issues and A/C compressor was not coming on. Will check power at compressor as well. Thanks for your help.

Recheck the power to the compressor after you replace the sensor, unless the compressor comes on of course. And have you had any other codes lately, I think you mentioned p2237?

Yes, have not had time to hack it up to check wires yet. Will do tomorrow.

Okay, let us know if you need any information or wiring diagrams. Hopefully your A/C will lick right on for you. Have a good day.

Replaced the ambient temperature sensor by touching the wires to it, nothing changed on the front display still shows -40, tested resistance between the two pins on sensor there is nothing. just like the old one.

The resistance reading should be at least 1000-2000 ohms depending on outside temperature. The readings to the ECM depends completely on the resistance of the sensor. It changes the voltage reading going to the ECM to determine outside temperature. Where did you buy the sensor at? And make sure your meter is on the right settings. But you should definitely have some kind of resistance on it. If it's an aftermarket part, it's probably bad. You may want to go to the dealership and get an Acura sensor. The -40 degrees is the default reading from an open wire or sensor. Same with the coolant temp sensor, goes to -40 when open circuit. Edit: there is probably a code stored for that sensor in the body control module or another module. It needs to be cleared when you put a new working sensor in. Edit: a coolant temperature sensor works the same way, resistance changes according to temperature.

https://www.2carpros.com/articles/how-a-coolant-temperature-sensor-works

Amazon. I returned it and ordered one form dealer.

Okay, I'm sorry for your frustration with this, these systems are complicated and we do get a lot of bad aftermarket parts. I always recommend getting technical/electronic items like sensors and modules from the dealership. I do believe there is a calibration process as well. I'll be looking for that information for you in the meantime.

what gets me is that why is there voltage cross the sensor wires, and only ground when testing with a test light, shouldn't there be power as well?

It's only a 5 volt circuit, it's probably not enough to light the test light fully. If you're reading 5 volts with your meter it should be okay. if that's the only broken wire you've found, I wouldn't worry about it until you get the new sensor in. If the compressor still doesn't come on, we'll have to figure that out when it comes to it. But that sensor is definitely an input for the A/C system. Check one thing, try putting the defrost on with the A/C, it might bypass that sensor. A/C is used during defrost because it's very dry air and aids in evaporating moisture from the windshield. Just see if the compressor comes on. It may not.

Good idea, will try it. But i also thought there maybe a way to bypass the sensor to confirm it is what is causing the issue.

You can put 12 volts to the compressor if it's "unplugged" for a few seconds, if you look on the diagram of the compressor circuit, you can see the light blue wire is the power coming from the relay, but it's risky doing that. If the wire touches anything it will blow a fuse to start with, and you don't want to damage any computer components or burn something up. I don't recommend it. I'm not sure exactly how many wires the compressor has going to it. But it might have a ground wire or pressure solenoid/sensor inside the compressor, and you definitely don't want to damage any of that. I was wondering when did you take those pressure readings from the first picture?

When as far as? Few days ago.

I had to look closer at the picture, the system has even pressures on both sides, which is good. The pressures should even out when the system is off.

tried defrost, didn't work.

Okay, so we'll move on to replacing the sensor and go from there. Provided there's no more wire damage. I think you'll be good to go. I've read that a bad ambient air temperature sensor will cause the compressor to not come on. So I think we're on the right track.

Replaced it with an Acura sensor and the harness connector. the display now reading okay, but compressor not kicking on. Tested the blue light while disconnected and it has power. So pretty much the compressor clutch? I seen people replacing just the clutch while compressor is still on the car, have you done that before?

Yes, you can replace the clutch without even taking the belt off. Here are some diagrams with instructions on the proper shim and clearance. Try tapping on the clutch and see if it will free up, you will still need a new one though. As long as your powers and grounds are good, it should turn.

Yes, tried tapping then and nothing worked , but i think belt needs to come off as the clutch is behind the pulley. the one with the electrical connector.

Yup you're correct, the belt does need to come off. Here's the instructions from All Data for A/C clutch replacement procedure .