A/C issue
Thread Starter
|
Junior User
Joined: Jun 2007
Posts: 53
Likes: 0
From: Central New York
A/C issue
Ok its starting to get warm here in NY and im chasing a problem with my A/C. It blows cold for a while when you first use it but after maybe 15 or 20 minutes it starts to get warm. If you leave the A/C running it will eventually cool off again, then the cycle repeats. I had the mechanic at work check it with his recycling machine and its got a full charge and I know the clutch is working, at least when I start it and try it out. Could I have a pressure switch thats on its way out? I think there is only one on the high side correct? If I need to change it can I do it without having the system evacuated? Thanks for any help guys!
More Turbo
Joined: Aug 2006
Posts: 530
Likes: 2
From: W. Wisc
Maybe the evap is icing up? If the low pressure switch (on the receiver/dryer) is not cutting out at the correct pressure, then it could be making the evap too cold and causing ice buildup. When that happens, cooling performance really drops until the ice melts, which could be the cycle you are seeing.
Another possibility is the clutch is worn and the gap is out of spec. Check with feeler gages - it should be no more than about 0.030". If it is bigger, then you would pull the clutch and remove a shim to get it back in spec.
Check the clutch gap and then get the readings from a set of AC gages and post back. Hard to do much diagnosing without that info.
-Dave
Another possibility is the clutch is worn and the gap is out of spec. Check with feeler gages - it should be no more than about 0.030". If it is bigger, then you would pull the clutch and remove a shim to get it back in spec.
Check the clutch gap and then get the readings from a set of AC gages and post back. Hard to do much diagnosing without that info.
-Dave
Thread Starter
|
Junior User
Joined: Jun 2007
Posts: 53
Likes: 0
From: Central New York
Ok I'll see what I can figure out on readings from the gauges. You obviously want the high and low side pressures correct? Is there a specific number I should be looking for? If it were icing, would I be able to physically see it? I see plenty of condensation on the lines but no ice. Also, when you say check the gap, what are you refering to? I'm mechanically inclined just not sure quite where I'm supposed to be checking. Thanks for the help! I have a rough idea of how it works in theory but no actual physical knowledge.
Last edited by cyclenut80; May 3, 2009 at 05:43 PM. Reason: typo
More Turbo
Joined: Aug 2006
Posts: 530
Likes: 2
From: W. Wisc
The evap is under the dash. Very hard to access.
Yes, high and low side readings. The low side should cut out around 25psi (the compressor clutch will cycle off). If it is going significantly lower than this, then you may be getting icing.
I wish I had a picture for the clutch as it is easy to show, hard to describe. Pop the hood and look at the AC compressor. When the AC is cycling you will see the "disc" on the end of the pully start to spin, and then stop spinning when it switches off. The gap is between that disc and the pulley. Check with the engine OFF, of course...
It could be a lot of things (compressor could be going, for one), but no way to tell without the gage readings and the clutch gap.
-Dave
Yes, high and low side readings. The low side should cut out around 25psi (the compressor clutch will cycle off). If it is going significantly lower than this, then you may be getting icing.
I wish I had a picture for the clutch as it is easy to show, hard to describe. Pop the hood and look at the AC compressor. When the AC is cycling you will see the "disc" on the end of the pully start to spin, and then stop spinning when it switches off. The gap is between that disc and the pulley. Check with the engine OFF, of course...
It could be a lot of things (compressor could be going, for one), but no way to tell without the gage readings and the clutch gap.
-Dave
Thread Starter
|
Junior User
Joined: Jun 2007
Posts: 53
Likes: 0
From: Central New York
Sorry it took so long to reply guys but anyway I did get some info. With the A/C running the pressure gauges are reading about 150psi on the high side and around 30psi on the low side. I have no idea if this is correct. The clutch on the compressor seems to check out ok too. Hope this may shed some light on the issue. The girlfriend is getting sick of open windows and messed up hair lol.
More Turbo
Joined: Aug 2006
Posts: 530
Likes: 2
From: W. Wisc
What was the ambient temp when you took those readings? Unless it was a cool day they are on the low side, which probably means it is low on freon. What is the cycle time on the clutch? It should stay on for a good 30 sec or more. If it is staying on only for a few seconds, then that is another key sign that the charge is low.
If it's low, then obviously you have a leak. If it is a very slow leak then perhaps just refilling a bit every couple years is OK, but the best course of action would be to find and fix the leak.
-Dave
If it's low, then obviously you have a leak. If it is a very slow leak then perhaps just refilling a bit every couple years is OK, but the best course of action would be to find and fix the leak.
-Dave
More Turbo
Joined: Aug 2006
Posts: 530
Likes: 2
From: W. Wisc
What was the ambient temp when you took those readings? Unless it was a cool day they are on the low side, which probably means it is low on freon. What is the cycle time on the clutch? It should stay on for a good 30 sec or more. If it is staying on only for a few seconds, then that is another key sign that the charge is low.
If it's low, then obviously you have a leak. If it is a very slow leak then perhaps just refilling a bit every couple years is OK, but the best course of action would be to find and fix the leak.
-Dave
If it's low, then obviously you have a leak. If it is a very slow leak then perhaps just refilling a bit every couple years is OK, but the best course of action would be to find and fix the leak.
-Dave
Trending Topics
Thread Starter
|
Junior User
Joined: Jun 2007
Posts: 53
Likes: 0
From: Central New York
It was about 65 degrees when these readings were taken. I do know that the clutch did not cycle at all over the time it was running which was about ten minutes. It engaged and stayed that way, this was with the truck at a dead idle and on max a/c setting.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
More Turbo
Joined: Aug 2006
Posts: 530
Likes: 2
From: W. Wisc
At that temp these readings are within spec. I'd say your AC is working fine. You need to look elsewhere for the source of the problem and that is likely either the blend door or the control unit acting flaky. Could also be a vacuum leak.
Evap icing is a possible cause too, if the AC isn't cycling off when the low-side pressure gets low (~25 psi). If that were the case, I'd change the low pressure cutout switch on the accumulator. Iced-over evap does not cool very well.
Good luck.
-Dave
Evap icing is a possible cause too, if the AC isn't cycling off when the low-side pressure gets low (~25 psi). If that were the case, I'd change the low pressure cutout switch on the accumulator. Iced-over evap does not cool very well.
Good luck.
-Dave
Junior User
Joined: Feb 2007
Posts: 53
Likes: 0
From: Tampa
Mine was doing the same thing. The issue was apparently the low pressure cutoff switch. (looks like a pressure switch screwed into the side of the accumulator). My neighbor vacuumed the system down and replaced r-134 and oil per updated specs from ford (3.5 lbs). We also cleaned the evap coil by removing the red sending unit in the blower housing under the hood. I also wrapped all the low hoses with a/c foam. Not sure that made a difference, but the hoses don't sweat now.
Truck blows nice and cold now. I should have replaced the low pressure switch a long time ago as the a/c really has never worked well in my truck. Now it will freeze you out.
You can just unscrew the low pressure switch without losing refrigerant. There is a schraeder valve behind it. The part was only $11 at the parts house. My neighbor works for a Chevy dealer, so they didn't have one at his shop.
Truck blows nice and cold now. I should have replaced the low pressure switch a long time ago as the a/c really has never worked well in my truck. Now it will freeze you out.
You can just unscrew the low pressure switch without losing refrigerant. There is a schraeder valve behind it. The part was only $11 at the parts house. My neighbor works for a Chevy dealer, so they didn't have one at his shop.
