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Auto_Enlightenment, ASE Certified Technician
Category: Car
Satisfied Customers: 237
Experience:  ASE Master Certified Technician
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just changed my compressor , had it vacuumed and air sometimes

Customer Question

just changed my compressor , had it vacuumed and air sometimes switches from front to back, but mostly blows in the rear. mechanic cant figure it out
Submitted: 4 years ago.
Category: Car
Expert:  Auto_Enlightenment replied 4 years ago.


Hello, I am an ASE certified Master Technician and I would like to help with your problem. Please refrain from rating my service until you have gotten what you need and are satisfied. If we can not figure this out together, rather then rating me negatively, continue our conversation so I can either make it right or opt out to see if another expert can help.

When the system is blowing, is it blowing cold? If you are just having blower issues than one of two things is happening here. Do you have it set to front blower and it just switches to the rear on its own or do you have both the front and rear on and the front just keeps going off?


If the system is just switching to the rear blower on its own then you have a bad A/C heater control panel. If both front and rear blowers are intended to be on but the front blower keeps shutting off then we may be dealing with either a bad front blower motor or blower motor resistor which regulates the blower fan speed.

I can walk you though checking these components if you feel comfortable doing so or can provide you with the information you need to pass on to your mechanic.

Customer :

the rear is blowing cold and fornt is blowing hot air. I thought it was cool air but, thats only when its cool outside


We need to check a few things. Have you had your refrigerant level checked to see if any has leaked out?

First we need to check the front expansion valve just before the front evaporator. There are two expansion valves & evaporators in your system, one for the front and one for the rear. The expansion valve is a critical component in the system and is the magical place where the cooling happens. Without getting too scientific, the a/c refrigerant pressure goes from very high to very loow accross the expansion valve. This process makes the refrigerant very cold before it goes through the evaporator. Warm air passes over the evaporator where the heat is removed and the air becomes cool.


The next thing to check would be the air blend door. There is a door in the front a/c blower/evaporator/heater case which moves to mix cold air from the evaporator with hot air from the heater core to reach the desired temperature selected on the a/c control panel. If this door sticks and does not move to the appropriate position then you will not get the cool air you are wanting.



Do you know if your mechanic has checked these things?


Expert:  Auto_Enlightenment replied 4 years ago.

Sorry, the chat mode was not responding so I had to switch to this format. We can continue our conversation here the same as before.

If the rear is cold and working properly then we know the core ability for the a/c compressor is good and that the system is able to cool. We now need to narrow down the problem with the front peripherals. I will be more than happy to walk you through some checks.