Have a 2010 Ford Focus, while driving on hot humid days the car goes shows overheat with A/C on, shut A/C off and back to normal temps
I checked low and high A/C pressure @90F they were 40 and 225, right about where they should be.
Any ideas what to check and what might be causing this problem.
Thanks all in advance

 

When you turn the ac on you should hear the radiator cooling fan(s) come on. Can you tell if that is taking place?

 

I have confirmed A/C prssures, fans are on
thanks

 

But are the fans running on LOW or HIGH? The fans will come on LOW when the A/C comes on, but when the engine temp rises to a given temperature, the fans should kick into HIGH mode. If they're not doing this, then that is your issue. The fix could be a number of things nowadays.

 

I will have to confirm that , I believe there are 2 relays that I have to check for low and high fan operation. Would an OBD find this ? I can confirm each fan run by applying 12vdc to plug on each fan, I already know one is working, I dont suppose the high speed will come on just sitting running will it. ? Thanks for the help.

 

Normally, just engine running will not have any fans running at all until the temp gets hot enough to kick them on. Then they will only normally run on LOS as that generates enough air flow thru the radiator to keep the coolant at its proper temperature. They will kick on and off as needed to maintain the temperature. Depending on where you live (hot areas), the fans may kick on high, but that would only be seldom. With the A/C running, it's an additional load to the engine which cases the engine to heat up faster and more often, thus the fans will kick on and off HIGH more often to get the proper air flow thru the radiator and condensor. Especially in stop-n-go traffic, or setting idling for extended periods.