1997 f150 AC problem
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1997 f150 AC problem
The AC in my f150 hasn't worked for years, back in 2010 when it was my dads he had a mechanic take a look at it and he said the compressor was shot that it needed replaced I am skeptical. The funny thing is that the AC lines in the truck get cold. I checked the pressures on the low side of the system with a can of 134A that had the gauge built into it. my low side pressure was like 45 psi I believe (in the green part of the gauge) which means my pressure are where they need to be. The strangest thing is that when i first turn my truck on and the engine is cold ac works like a dream for like 5-10 minutes. After my engine warms up it starts to warm up until its blowing hot air. What do you guys think I should do/look at next. Thanks in advance for all replies!
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the low side is about 45 psi and the high side is about 200 psi... motor off they will "average" to get 100 psi on both sides... see if you have that... Start motor and engage clutch ( compressor) and the LOW side goes down to 25-45 range....Just set in driveway and watch the gauge and clutch.. Put something against the throttle cable / lever to hold motor at 1800- 2000 RPM ( highway speed)... LOW gauge will pump down to 25 psi, then compressor kicks out... pressure starts to climb and compressor will kick back in at 45 psi and start pumping.. and drop pressure... see if all that happens. put a thermometer in the dash vent and see you have 55 degrees ( maybe 60-65 on old system?) .......... the compressor should run for about 30 seconds, then cut off for 10 seconds.. if you don't have enough run time, you are low on gas and the cooling is effected... If all works and you have HOT air, then the blend door is bad.
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the low side is about 45 psi and the high side is about 200 psi... motor off they will "average" to get 100 psi on both sides... see if you have that... Start motor and engage clutch ( compressor) and the LOW side goes down to 25-45 range....Just set in driveway and watch the gauge and clutch.. Put something against the throttle cable / lever to hold motor at 1800- 2000 RPM ( highway speed)... LOW gauge will pump down to 25 psi, then compressor kicks out... pressure starts to climb and compressor will kick back in at 45 psi and start pumping.. and drop pressure... see if all that happens. put a thermometer in the dash vent and see you have 55 degrees ( maybe 60-65 on old system?) .......... the compressor should run for about 30 seconds, then cut off for 10 seconds.. if you don't have enough run time, you are low on gas and the cooling is effected... If all works and you have HOT air, then the blend door is bad.
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Joined: Jan 2004
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From: St Louis
The strangest thing is that when i first turn my truck on and the engine is cold ac works like a dream for like 5-10 minutes. After my engine warms up it starts to warm up until its blowing hot air. What do you guys think I should do/look at next.
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Does the clutch stay engaged or does it cycle on and off?
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Just played with my truck and some gauges in the driving way. Turned it on let engine warm up, turned ac on max and opened up the windows. My pressures settled at 40 psi on my low side (45 degrees) and 150psi (110 degrees) on my high side, Would you say thats low? or would you charge it to that 200 psi on your high side? My clutch was engaged the entire time.
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From: St Louis
Insufficient preparation. You need to have the engine running at the recommended speed for system check-out.
A fair rule of thumb is that the high side should be running between 2.0X and 2.2X the ambient in degrees F.
A fair rule of thumb is that the high side should be running between 2.0X and 2.2X the ambient in degrees F.
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kevin, the 45 psi and 200psi I listed are not EXACT... AS mentioned, it depends on ambient temp, engine speed, etc... Those numbers were just to get you on the right track... Increase engine speed and see what happens to your 40 psi.. If the compressor starts to cycle, see how often it does... If your holding at 40 psi and the compressor is constantly ON, then it don't look like you need more gas at this time......
are you getting COLD air out of the dash vents ?
are the lines ( aluminum) around the compressor and coil COLD and HOT like the system is working ?
are you getting COLD air out of the dash vents ?
are the lines ( aluminum) around the compressor and coil COLD and HOT like the system is working ?
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The only thing that is absolute in car AC is the total weight of refrigerant. All others (low side P, high side P, temperature) are relative. That is why car AC diagnosis is difficult and may seem to be bogus to weekend mechanics like us. I wouldn't be overly attentive to 150 psi high side pressure and would take advice from experienced members (projectSHO, alloro, steve).
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Big Norm
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Sep 16, 2013 09:53 PM