Hi all. Im new here and hope to get some help, I have an 88 F150 4X4 w/4.9 engine. When I bought the truck the AC lines were not hooked up and there wasnt a condenser in the truck. Also the turn signal switch had to be replaced. Well after replacing the signal switch I tried to start the truck without success. I changed everything on the ignition and was about to change the fuel pump. After doing some reading online I read that the EEC could be bad if the fuel pump ran continuously (which mine was). So I decided to change the EEC. It worked!!! The truck started. Well I didnt mess with anything as far as the heater or AC because I was afraid something might happen. Well I was off work this week so I decided to put a fuse in the AC/heater slot just to see. Turned the heater on while the truck was running. All was good. Now switched over to AC controls then pushed the blue illuminated AC button in and the truck died. tried to start it and it wouldnt start. Also noticed the fuel pump was running continuous now. I knew exactly what the problem was. The EEC fried again. It has a 1 year warranty and a new one was overnight shipped. Put the new one in and it fired right up. My question is this. Would the AC system not being charged cause the EEC to fry by pushing the blue lighted AC button? Is something in safe mode or maybe a bad compressor? I want to install a new condenser and get the AC going again. Everything else is there. Just afraid of frying the EEC again. Sorry for the long post but i needed to explain in detail for better help. Thanks in advance

 

When you turn on the A/C you put battery power on pins #10 (348) and #43 (347).
The computer should handle normal battery power at these pins.

The running of the fuel pumps is because the clock is not running in the computer. The clock must run for one second before the logic turns the fuel pump relay off.

I see no rhyme or reason for the battery power being applied to these two pins would hurt the computer unless the battery voltage or a voltage spike was too high.
I do not know how an never heard of it but I guess the A/C clutch wiring could act as a auto transformer (same as an Ignition coil) and put a very high voltage spike on these wires.

So I guess you could unhook wires #347 & 348 and see what happens.
I would also check to see what voltage the alternator is putting out.

 

The fuel pump only ran continuous after the EEC went out(fried circuit). It does shut off now after 1-2 seconds with the new EEC. The alt voltage is 14.1