Good AC question
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Junior User
Joined: Nov 2010
Posts: 83
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From: Katy TX
Good AC question
Have an 04 F-350 with powerstroke.
If the temp out side is under 93 degrees the ac works fine, it will freeze ya out of the truck. If the temp gets over 93 degrees it works fine for maybe 20 miles, then blows hot air. I turn the ac off for ten minutes and turn it back on it will blow cold again for about five miles and blow hat air again. This has been goin on for a couple of years. What could it be?
If the temp out side is under 93 degrees the ac works fine, it will freeze ya out of the truck. If the temp gets over 93 degrees it works fine for maybe 20 miles, then blows hot air. I turn the ac off for ten minutes and turn it back on it will blow cold again for about five miles and blow hat air again. This has been goin on for a couple of years. What could it be?
Fleet Owner
Joined: Jan 2004
Posts: 26,007
Likes: 575
From: Brentwood,CA
The humidity is causing the evap core to freeze up. With high humidity you need constant air flow over the evap core so you must run it on high with all the vents open. If that does not work its a system pressure issue and an easy fix.
Fleet Mechanic
Joined: Feb 2006
Posts: 1,776
Likes: 5
From: Lorain County, Ohio
Check the compressor clutch when it starts to blow warm. Is it engaged?
If so, The evaporator is probably iced up. If the lines going into the firewall are iced over, that's a dead giveaway.
This can be caused by a bad Low Pressure Cutout Switch keeping the compressor engaged when it should cycle off. The switch should be located on the accumulator or on the suction line (evaporator to compressor line).
It's also possible that a slightly low refrigerant charge can cause evaporator icing, but a failed LPCO is much more common. You would need a manifold gauge set to check the system charge.
If so, The evaporator is probably iced up. If the lines going into the firewall are iced over, that's a dead giveaway.
This can be caused by a bad Low Pressure Cutout Switch keeping the compressor engaged when it should cycle off. The switch should be located on the accumulator or on the suction line (evaporator to compressor line).
It's also possible that a slightly low refrigerant charge can cause evaporator icing, but a failed LPCO is much more common. You would need a manifold gauge set to check the system charge.
Fleet Owner
Joined: Jan 2004
Posts: 26,007
Likes: 575
From: Brentwood,CA
The above nailed it check for a low pressure condition at rpms above idle. This can be a real simple fix. You want to be in the 34-42 psi range at 1500-1900 rpm's and up to 45 at idle depending outside air temp.
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Junior User
Joined: Nov 2010
Posts: 83
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From: Katy TX
When it blows hot air the compressor is not on. The lines have not froze up that I have seen. I replaced the low pressure switch last year. The next time it starts blowing hot air I will Pull over and double check and see if the lines are froze up. I have been waiting until I get home to check this in the past. Thanks
Hotshot
Joined: Jan 2004
Posts: 19,760
Likes: 1,079
From: St Louis
Evaporator icing is usually accompanied by a reduction if airflow through the outlet vents an the air that does come out is moist and humid.
You might simply have a excessive clutch gap or a weak clutch coil that fails after a certain amount of heat is absorbed from operation and resumes after it cools a bit.
You might simply have a excessive clutch gap or a weak clutch coil that fails after a certain amount of heat is absorbed from operation and resumes after it cools a bit.
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i ain't rite
Joined: Mar 2005
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From: Marlboro Mental Hospital.
my crown vic does the same thing every few years with the evaporator core freezing up. . top off the freon charge and all is well in AC land again.
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Fleet Mechanic
Joined: Feb 2006
Posts: 1,776
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From: Lorain County, Ohio
Ya might want to check out that switch before you go screwing with the refrigerant level. It's the more common of the 2 causes, by far.
Mountain Pass
Joined: Sep 2002
Posts: 148
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If the system blows hot air only when the temperature outside is above 93 degrees, or let's say "hot", I suggest that your problem is that the pressure is getting too high. This is the only possibility if the problem is really related to outside temperature and the refrigerant charge is correct.
If the system has not been worked on by "a/c mechanics", ie, has the same charge it has had for years, and you have not added freon, ie, too much freon, then you should check the radiator fan clutch. Do you hear it roar after you have idled for a while and it's hot out, or after you stop the truck with a/c on and it's hot out then go again? You should.
So, either the fan clutch is shot and you are not getting enough air flow across the condensor to keep the pressure down, or the system is overcharged or both.
If the system has not been worked on by "a/c mechanics", ie, has the same charge it has had for years, and you have not added freon, ie, too much freon, then you should check the radiator fan clutch. Do you hear it roar after you have idled for a while and it's hot out, or after you stop the truck with a/c on and it's hot out then go again? You should.
So, either the fan clutch is shot and you are not getting enough air flow across the condensor to keep the pressure down, or the system is overcharged or both.
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Junior User
Joined: Nov 2010
Posts: 83
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From: Katy TX
OK, I pulled over when it started blowing hot air, this is what I found out so far. The conpressor was not running, the low side was real cold but not frozen, the electric fan was blowing. I replaced the low pressure swich. I am going to borrow some gages tomorrow, it will be 95 to 100 degrees out tomorrow. What should the pressure be at this temp? If the low pressure side is low do I add, and if it is high do I let some out?
Thanks guys this fourm has help me replace the ball joints and the water pump, man ain't the internet great or what!
Thanks guys this fourm has help me replace the ball joints and the water pump, man ain't the internet great or what!