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'99 F-150 a/c needs diagnosis

911Targa on Fri June 24, 2011 7:48 PM User is offline

Year: 1999
Make: Ford
Model: F-150
Engine Size: 5.4
Refrigerant Type: 134a
Ambient Temp: any
Pressure Low: 40-45

I have a 1999 Ford F-150, 5.4 V8, approx. 115k miles & I am the original owner. Over the years the a/c has always worked fine until six months ago.

With the a/c controls in the correct positions & the blower on, the air temp out the vents is warm to very warm depending on the ambient temp. The belt to the compressor is good, but with the engine running, with the a/c on, the compressor clutch will engage but the compressor will only run for a few seconds 5-10 then cycle off for 15-20, then repeat.

I took a low side pressure reading when the engine was off and it was around 40-45psi, so I was believing that the 134a was still in the system, meaning “no leaks”??. Every time the compressor stops while the engine is running, you can hear a “click” sound, like a relay, near the firewall under the hood but I don’t know if this is related. Also I saw a few vacuum hoses that were cracked under the hood due to age.

Any info will be appreciated!


bohica2xo on Fri June 24, 2011 8:16 PM User is offline

With 40 psi static, the system is basically empty.

You have a leak. The system is short cycling, which is normal when it has little refrigerant. The leak should be located and repaired.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Johno on Sat June 25, 2011 10:37 AM User is offlineView users profile

Sounds like your system is empty. Check all hoses and fittings for evidence of leaking and if you fail to find anything there you should also check the condenser and evaporator coil as these can leak from damage or become porous with age.

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