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Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8598
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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I have a problem with my a/c, it works fine when i am

Customer Question

I have a problem with my a/c , it works fine when i am driving buy as soon as i am in traffic for more than 10 min it stop working
Submitted: 1 year ago.
Category: Mitsubishi
Expert:  Doug replied 1 year ago.
When you are in traffic and the AC stops blowing cold, does it resume operation once you are in motion again at speed?
Customer: replied 1 year ago.
Not really the ac light blinks and after a get home and next day i turn my car on everything works fine
Expert:  Doug replied 1 year ago.
When the vehicle is only driven at highway speed or thereabouts, does the AC continue to work normally?
If you turn the engine on and AC on, do you hear the fan turn on under the hood?
Customer: replied 1 year ago.
This is my wife car so I haven't been driving it until today and i am testing it out to see what is wrong .
Ok I left my house and drove to bank 3 miles away after a mile i was sitting on a light for while and right after i started to move and a/s stopped working blinking light came up and the radiator fan stopped blowing . I turn a/c on and off but nothing happened the light was still blinking. I pulled to the parking lot and turned the car off for 5 min and turn car back on again and a/c is working fine
Expert:  Doug replied 1 year ago.
With the fan operating as it should on the radiator, it is most probable there is a charge level issue going on.
When the system is shut down like this (ac light flashes, outside fan turns off) it is indicating the ac ecu requested the system be turned off to protect itself. There are several reasons this can happen:
Under charge condition (pressure too low)
Over charge condition (pressure too high)
Rotational conflict from compressor (compressor turning too fast/slow when compared to the engine, usually as a result of charge level but also clutch failure can do this)
Thermistor on evaporator reading too cold
Pressure switch malfunction
Since the problem is only prevalent when the vehicle is stationary long enough, this pretty well rules out the pressure switch as well as rotational conflict. This leaves us with our most likely suspects to be the system over cooling the evaporator or pressures going out of range at idle.
Since the system has been topped up, this actually worsens the condition... if the charge level were correct of course now it would be over-charged, but if it was low as expected and was topped up this would add refrigerant on top of the air/moisture that was introduced from the leak, making the system far more prone to pressure malfunctions (not to mention being very hard on the compressor and the drier).
Before doing anything else, get a base line operation first by recharging the AC properly. It is certain to be incorrect now regardless as noted above, so it needs to be done no matter what anyway. Have the system evacuated to see how much refrigerant was actually in there, then have it placed in a vacuum for 30 minutes to boil off any moisture introduced before, and finally have a scaled charge put in to be sure that the correct amount is in there. As little as 20 grams off can make a substantial difference in the operation of the system, making a scaled machine charge absolutely mandatory on these cars... you can not guess/wing it on these successfully.
With the system vacuumed out for moisture and with a proper precise charge, then check operation... it is nearly certain to be correctly operating after that. Since almost all shut down scenarios involve a charge level issue and since the fan operation is OK and driving operation is OK, and as well we know the charge level has been modified, this is nearly a sure thing. To go beyond that would be pretty unlikely given the circumstances (if the evaporator thermistor was reading wrong it would do this, but not be dependent on sitting still; same goes for compressor failure).
Customer: replied 1 year ago.
It this something i can do it myself ?!
When a/c works fine i attached a gauge to the recharge valve and it was showing the about 250kpa or 35 psi
Expert:  Doug replied 1 year ago.
You need an AC recovery machine to properly evacuate the system and to remove the moisture from the system via vacuum, and of course to perform a scaled charge. Again this system can malfunction from as little as 20 grams off in charge, so there is no way to get around this and have a 100% functional system.
Checking low side pressure unfortunately means absolutely nothing... which is one of the many reasons those "DIY" AC cans are a terrible, terrible product. They are great for putting gas in an older car you are getting ready to sell, but on a modern car that more carefully monitors pressure they are much less useful, and for a car you plan to keep they are down right detrimental as they promote water in the system which will cause a compressor and drier failure in the future.
The problem with low side pressure is that it tells nothing about the state of charge other than "not empty" and "not ridiculously overcharged". You can have a system showing 35-50 psi low side and 100 psi high side and be completely inoperative, you can have 35-50 low side and 220-250 high side and most likely be working (depending on contaminants) and you can have a 35-50 low side and 320 high side and be intermittently inoperative. Basically... the high side is far more indicative of what is going on, but because it is handling pressures that can cause serious physical injury, none of those DIY kits will allow adapters for that (or a gauge that could hold that sort of pressure anyway).
Again while we have other possibilities, they are few... and we KNOW without a doubt that the pressures are incorrect... either due to them being good to begin with and you over charged it, or them being low to begin with and you charged an unknown amount without removing the air and moisture from the system first. Before any accurate diagnosis can be done on the AC the charge level has to be precisely correct... meaning the right weight of refrigerant in the system, no air in the system, and no moisture in the system. That is why all AC diagnostics start with evac and recharge proper level when it is unknown. It just so happens that it is highly likely to correct your issue as well, but regardless must be done first.

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