hello I'm new to the page. i bought a g37x sedan 09 a couple of weeks back, the AC won't work unless the car it's cold, and then it would work for a couple of seconds.
,then it will blow hot air once the car temp reaches normal. I have changed low pressure switch, the ipdm and the climate control and audio unit, And nothing. The AC pressure it's fine. Now I think the compressor and clutch of the AC works because when the mechanic hooked it up directly with the battery it blows cold. I'm running out of money I really need your help. Thanks in advance.

 

Are you saying that the AC blows cold when you first start the engine, but as the engine coolant warms up the air from the AC starts getting hotter?

If so, then it sounds like the air mix door is stuck- in this case on full heat. Best way to test this without getting too complicated:

In as quiet a area as you can:
-Turn the key to ON but DO NOT start the engine;
-Set the blower to LOWEST speed and make sure the Radio is OFF;
- After the seat belt warning stops chiming and with your ear as close to the bottom of the glovebox as you can (easier to remove the glovebox), turn the TEMPERATURE dial from 60 to 90. As you turn the dial you should hear a slight "whirring" noise for a few seconds. This is the AIR MIX door cycling from full cold to full hot.
- Then, turn the TEMPERATURE dial from 90 to 60 and you should hear the same sound as the AIR MIX door cycles from full hot to full cold.

If you do not hear anything, then likely your air mix door is not working. From there you will have to find the door and check the electrical connection and if the door is free to move.

I would suggest you download a copy of the Factory Service Manual (FSM) for your car as this will prove valuable when working on your car. Here is a link to the entire index: 2009 G37 Sedan FSM
In this case you will want section HAC (Heater and Air Conditioning Control System) for this issue but I would recommend you download the whole manual.

There are also other self-diagnostic tests you can run to further narrow down your issue. Friendly advice, though: Do NOT start throwing parts at something unless you know for certain what the root issue is first.

Hope some of this helps.

 

Thanks for the manual and seems to make the door opening noise only when I put it on hot because when I put it on cold the door makes a quieter noise

 

Still, it would not hurt to check the air mix door to make sure it is moving freely and fully. The door should move smooth. A little shot of grease/lube might help regardless. Also, check to ensure all electrical connections are secure.

With the air mix door set to FULL COLD (A position) you should not be getting any hot air from the heater core- only cold air from the evaporator. The unified meter AC amp modulates the air mix door between positions A (full cold) and B (full hot) to achieve desired temperature setting. If you are still getting hot air with the door fully set to FULL COLD then there is a separate issue with the AC system.

 

Another additional info I also noticed the AC lines stop being cold once the coolant warms up

 

Sounds like there might be something else going on...

At this point, I would recommend you run the HVAC self-diagnostic protocol and see if there are any codes stored that might help narrow down the issue. There is a extensive write up in the FSM that has everything broken down. If everything checks out, then you have to look into the refrigeration side of the equation.

The plot thickens...

 

ILM has provided some great detail but have you tried checking your refrigerant levels? My car did the same thing as yours and long story short, I had a hole worn in my low pressure hard line. I replaced the line, refilled the refrigerant and now I'm good to go.

 

RMB, I had thought of low refrigerant at first, but OP states that the AC is cold at startup but as the engine coolant warms up the discharge air gets hotter.

The only reason I suspect the air mix door is from experience. A long time ago my AC "went out" on my old Civic. No matter what I did I couldn't get cold air once the engine warmed up. Took me forever until I figured it out- a oak leak somehow managed to jam the air mix door half way. At least I could take the roof off and open the back window for some cooler air.

Still worth checking, though... Maybe OP will have luck pulling some codes from the self-diagnostic function.

 

I was doing some diagnosis from the manual u send me and one that concerns me is the ambient temp sensor because the reading it's not the same as the actual temperature reading also I noticed that the cooling fan it's allway on even when car is cold now I know the cooling fan and the AC fan are connected to the same relay in the ipdm soo maybe it has something to do with each other
PD thanks for the input guys I appreciate your help u have no idea.

 

Look at lower part of dash near steering wheel you'll see a vented slot that has a tube connected to it that the car uses to read temp inside

 

I'll check that out

 

UPDATE!!!
I did the ipdm diagnostic and Everything checks including the compressor clutch. I removed the glove box and the mixing door it's working perfectly. I say the only thing left is the temperature sensors.

 

Sounds like you are making some progress. I do agree with Surfna*i to check the aspirator (vent next to your right knee). It might be possible that the tube is loose/pinched or that the sensor kicked the bucket.

With regard to the fans, even with a stone cold engine, if the AC compressor is engaged the fans are running.

IIRC, the ambient temperature sensor is located near the front bumper and shows the ambient temperature on the center display/gauge cluster. Because it is up front, the actual temperature can vary because of heat being rejected by the radiator/condenser. They are not that accurate to begin with, however, I do not know offhand if the climate control uses input from this sensor or not to regulate cabin temperature.

I hope you figure it out. If I can help...

 

Well the manual says they are related to the AC and how do u remove the sensor inside the cabin I know where is it at but don't know how to remove it

 

It's a hose that connects to back side of lower dash feel around for it and plug it back I