Ok, since your High side or head pressure is normal or with-in range. We can safely assume the system is not low and there’s probably no restriction in the lines.

Now your suction pressure is low so let’s review the possible causes of a low suction.

1 – Low on charge, but no that would cause a low head also.

2 – Restriction but, that would cause a high head pressure

3 – Lack of airflow across the evaporator coil will cause a low suction also. There are many causes of low airflow. No blower motor, dirty coil, dirty filter or a crushed duct.

But, in the beginning you verified that your blower motor was running and you already checked the air filter. So that leaves two choices a dirty coil or a crushed duct.

Go to the indoor unit and double check that the blower motor is running by sound and vibration.

If the motor is not running then you should stop right here and move to page 28.

Lets go to step 28 now

If you’re blower fan is running, like we thought earlier then continue on down the repair matrix.

Open up your evaporator coil and visually inspect the coil for dirt.

(Note: Dirt will collect on the side of coil closest to the furnace.)

If your coil is dirty then the only repair option is to acid wash the evaporator coil, so move to page 8 now and do that.

Let’s go clean an evaporator coil

If the coil is not dirty, then look for a crushed return air duct or a clog in the duct.

(Note: sometimes a piece of insulation can get sucked up and clog ducts.)

If you have no airflow issue then were left with one option, you have a restriction. Yes, I know we said there’s probably no restriction earlier but, now we have eliminated every other option for the low suction except a refrigeration issue so move to page 19 now and perform yourself “a fix all” clear a restriction, remove screen, change filter drier, vacuum and re-charge with fresh R-22 and that my friend will repair any air conditioner that has a working compressor and 2 working motors guaranteed.

(Note: A fix all is my term and I love fix all’s. What it is, is this during certain repairs, it is very easy to include other repairs while you’re already knee deep into the system. For instance when we have a system open or void of Freon to change a compressor it’s easy to replace the filter drier and clear out the metering device before putting the r-22 back in the unit. That way you address the compressor the electrical and you clear out a restriction, so basically the machine has to work afterwards. Or while you are changing a filter drier outdoors and the system is void, go inside open the metering device, remove the screen and blow both ways with nitrogen to clear any debris.)

"Fix All" restriction repair

If the motor is not running then you should stop right here and move to page 28.

If your coil is dirty then the only repair option is to acid wash the evaporator coil, so move to page 8 now and do that.

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