A/C mystery

So, you fellows are awfully smart and I want to run this one past you, it’s got me befuddled.

I’ve been trying to diagnose Mary’s Ford Ranger which has some A/C issues. She thought the A/C didn’t work at all, and drove 6 hours in the heat without it… It actually does work, but only after running the engine for approximately 20 minutes. It can be running at idle, or on the highway, the timing is the same. Usually it comes on for a bit, then stops, then comes back on to stay. Once running it works great until you shut the engine off again for a long time. Brief stops it will still take a minute but comes back much faster. This makes me think the problem is somehow temperature related.

I’ve checked the refrigerant pressure, it is within the “good” zone while the compressor is running. Also when it does come on, it feels good and frosty. Could low refrigerant cause this somehow? The compressor does not even kick on for 20 minutes, which is the strangest part of all this.

If it’s freezing up, wouldn’t it cool first and then stop? It seems to work indefinitely once it starts.

If it’s airflow related, it would not come on parked at idle, which it does (eventually).

If the compressor was overheating, it would work at idle but not while driving. So it’s not that either.

For what it’s worth, the blower resistor is also bad, only the high setting works. I believe that is unrelated, and all my testing has been done using the high setting.

intermittent fault on the relay?


Intermittent = temp sensitive? Possibly. I’ll see if I can locate the relay.

Bypass the electric system from the A/C by direct applying voltage to the clutch from the compressor, be it that your fan must be running of course…

If it runs cold then you’l know that its the electric system .

As you already mentioned, if the resistor is not ok, then probably its also fidling around with your voltage going to the clutch. No fan blowing = no voltage towards the compressor clutch.

My 2 cents…


Here are some forum postings that describe the same problem, with possible solutions: A/C Problems in an 02 2.3l - Ranger-Forums - The Ultimate Ford Ranger Resource

Hi Cris, jump pressure switch when cold, if runs bad switch, if not could be the in line filter starting to plug(takes a while for pressure to build) Could also be a drier getting saturated.

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@dbaillie gets the prize, it was indeed a bad relay. Swapped out, compressor started right up. Blower resistor replaced as well, now system is 100% functional!

Thanks for all your input! You guys are the best.


Hi chris i reallize your ranger is fixed now, but under built relays seems too be steady job these days of enjineering, on appliances and automobiles. 2 of my s10 trucks have faulty relay repairs yet too be changed. Allso i think a lot of the wireing is barely heavy enough.My oldest brother is allways fixing broke stove ovens from cooked or faulty relays on the boards, he resolders in new relays too fix.