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It’s about that time for people to start noticing they don’t have a compressor kicking on!
don’t forget you Diode! Driver side under hood junction box If the clutch doesn’t kick on pull it and if it works without it in that is your problem. ( my experience I kept popping fuse 11 and it was my diode.
if all fuses are good you can jump your relay inside junction box under hood to cut on compressor to check refrigerate level.
Check refrigerant on high port
Repeatedly Blowing Fuse: Frequently caused by a short in the AC clutch coil.
No Power to Compressor: Check Fuse 32 and swap Relay R202 to see if it fixes the issue.
No Power at Switch: Check Fuse 11 and 14.
High-Side Pressure Check Procedure:
Locate Port: Find the high-side service port (smaller diameter metal line, usually near the passenger side firewall or compressor).
Connect Gauge: With the engine off, connect the red hose of a manifold gauge set to the high-side port.
Monitor Pressure: Start the engine, turn the A/C to max cold, and high fan speed.
Readings:
Normal: 150-200+ PSI.
Low: Often indicates a leak.
Over 300 PSI: Indicates a restriction or failing cooling fan.
compressor clutch- (but that’s getting away from simple checks)
Use a feeler gauge to measure the clutch gap. IIRC, gap should be between around .15-.030"
High port
Last edited by 05F1504x4; Apr 2, 2026 at 03:34 PM.
The diode is not there to make the clutch work, it's there to protect the rest of the vehicle's electrical systems from a potential surge when the clutch de-energizes.
The only way the diode can cause the A/C system to not operate is if it shorts and causes the fuse that supplies the clutch to blow. BTW, if you manage to put it in backwards, it will behave just the same as if it was shorted.
The diode is not there to make the clutch work, it's there to protect the rest of the vehicle's electrical systems from a potential surge when the clutch de-energizes.
The only way the diode can cause the A/C system to not operate is if it shorts and causes the fuse that supplies the clutch to blow. BTW, if you manage to put it in backwards, it will behave just the same as if it was shorted.
Yes I understand that but it is a simple check that could be the issue. we are talking Simple checks. Simple is the key word. No wiring scematics no complex machinery or computers etc, no clutch replacement. Just simple.
Yes I understand that but it is a simple check that could be the issue. we are talking Simple checks. Simple is the key word. No wiring scematics no complex machinery or computers etc, no clutch replacement. Just simple.
Let's make it even simpler, then. If the clutch coil supply fuse isn't blown, the diode check isn't relevant.
My A/C kicks on just fine - but I am probably going to have to get the refrigerant recharged. It blows cool and the little light comes on, but it's not COLD. It worked fine last year, of course.
The old girl is 22 years old now and - even with low mileage - it is not unreasonable that some R134a needs to be added. Even a tiny leak somewhere will eventually afflict any system. 2004 F-150 XLT 4x4 - 63,000 original miles.
Evacuate and recharge to get any air and moisture out (best solution) IMO
That is what I do some of the older ones that still work and cool
You could always add a bit or freon, but an Evac and Recharge is better
Adding freon on top of some air will up the pressures, but not up the system performance much in some cases
I have 2 recyclers and can do it in 40 minutes is the other reason I do it on a regular basis
Consider finding someone like me who will do it for you for 100 bucks
Otherwise, you can pay to have the freon removed and then evacuate it yourself, for as long as you want, then recharge it
A/c check! Summer time!!!
