88 F150, 300.

So the rusterection of this old beauty continues. It has been hard since it turned into my daily driver, but I have gotten a few of the old problems out of the way:

Timing was a bit off, one spark plug was cracked and the rest were gapped wrong. All of this has been fixed. Gas leak was fixed with a new gas line and the brakes were fixed with new wheel cylinders, a new master cylinder and some good bleeding. Numerous other issues have been fixed, sensors going bad and wiring problems.

After all of this I started to work on the annoying things and I have come into two issues.

1. A/C was converted by the state (Truck was a state truck before it went to auction. I bought it from a friend who bought it from said auction). It was holding vacuum, but was not charged, possible that they converted it when they put it up for auction and didn't charge it. When we tested to see if there was pressure, there was air movement into the system, so it was still vacuumed.

We charged it up and let it run. The A/c compressor will click in, spin and run for 12-15 seconds before cutting off. No air comes from the vents in the cab on any setting. The compressor will turn itself back on and off without problems at regular intervals. All tubes leading out of the compressor build condensation and get cold. Same with the condenser. I put 3 cans (32-35oz total) slowly into the system. Once there was enough the compressor started to come on (Which it would not do before) and would stay on longer and longer until I hit that 12-15 second max.

The heater does not work on any setting either. I haven't looked at any mechanical parts for it so far.


What would cause the air not to blow into the cab? Are both systems hooked up to a fan in the dash that could be bad and not moving the air? Since neither work I would like to look there first to determine if that is the case.



2. The ECT wiring harness is bad. It is bad directly in the clip that plugs into the ECT. I traced down this check engine light for days when it would blink on and off randomly while I was driving. Basically if I press it on tightly, it runs perfectly till it vibrates loose. Turns out the clip was broken.

Since the wires for the ECT run under the manifold on the 4.9l, what is the best way to replace the ect harness and where does the wiring harness draw power from? I know it runs to the back of the motor but I am not positive where it goes from there.

Anyone have any experience replacing this little dastardly gentlemen of a piece?

Thanks for the help guys. So far it has been a blast. If I can get the ect and the A/c working then it is on to replacing the wheel bearings and setting up the radio. Coming along great.

Jeremy

 

Well as far as the blower motor for the cab goes, it's an easy enough thing to troubleshoot. And by "easy enough" I mean the process itself is easy- actually getting to the blower motor may be a different story.

1) Since you checked the fuse and it's good, you need to find out whether or not voltage is reaching the blower motor. You can do this by back probing the connector for the blower motor (the motor itself, NOT the resistor). Make sure to have the fan selector switch on high, then check for voltage. One side of the connector should show battery voltage and the other side should show near zero voltage.

If you DON'T have battery voltage at the blower motor, there is a problem "upstream" of the connector at the blower motor. You need to trace the circuit back to the source (fuse box) and check any connections you find along the way for battery voltage. THIS IS WHERE A WIRING DIAGRAM COMES IN HANDY - troubleshooting the circuit will be much easier if you have it.

If you DO have battery voltage at the connector but zero volts at the other side, there is a grounding problem and you need to chase the ground wire. If you don't find any problems with the ground circuit, then the motor is bad and needs replacement.

 

Thanks a ton, I'll follow that guide tomorrow and see what my trusty voltmeter comes up with.