I have a 05 freestar. My air conditioner used to run you out it was so cold. Now it only cools well if i am on the highway or its not real hot outside.

I thought i was low on ac coolant so i got some and it is full.

I check the radiator full/coolant ok.

Any ideas of what I can tell the mechanic to check?

 

I had the same issue with my A/C. Turned out to be a burnt out modual in the fuse box under the hood with some burnt wires. Mechanic replaced and workin great.

 

Without putting gauges on the system, one doesn't know how much freon is in a system. TOO much freon will cause poor cooling problems. Normally, good cooling when driving at higher speeds, but poor cooling when stopped or at low speed is an air flow issue. Have your cooling fans or fan clutch checked. Good airflow across the condenser and radiator are important for a properly working system. As soon as you turn your A/C, both cooling fans should come on at the low speed setting. Check to make sure that they are working correctly. Also, make sure the condenser is clean; free of bugs, debris, large plastic bags that drift up there. Blocked airflow will also cause poor cooling.

 

Have you replaced the cabin filter. Are you getting cold air a the vents just not cooling the interior well? Restricted airflow with in the heating cooling system will allow cold air at the vents but not enough airflow to cool the car. Had a problem like this in a GrandAm were a small leak allowed oil and dust to restrict airflow in the system, temp at vent was below 50 but car interior would not stay cool unless running at hiway speed.