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Discussion Starter #1 (Edited)
I left home in the heat today and the AC worked good. Coming home I noticed it wasn't as cold as it was when I left home and actually got warm. I then caught sight of my engine temp gage. It was way high. Usually runs in the middle, but was 3/4 to the H and climbing. I shut off the AC and the engine temp went back to normal. Tried the AC again and it was somewhat cool...not cold and wouldn't get any colder. The after about 3 minutes, the engine temp started to rise again. With the AC off, the temp stays in the middle as normal, even though it is 90 dgrees out with a heat index of 96.

Had a problem with it quitting for no reason a couple years ago and finally removed the shim washer on the clutch plate bolt to reduce the gap between the plate and magnetic coil. This worked up until today.

What do you think?

On edit: Just saw on another thread you can buy just the clutch plate. Where???? I've only seen them come with the coil as well. I don't need the coil.
 

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Discussion Starter #2
Just tried it idling in my driveway. Clutch seems to engage OK. HArdly any cool air coming out and no engine overtemp at idle speeds. Heard fan kick in also. Don't know if it was the condenser fan or the engine cooling fan. Probably the condenser fan becasue it came on as soon as I turned the AC knob to Max AC.

Think I'll go buy a can of coolant and try it. Can't remember if the low side port is the one with the black rubber cap or the green.
 

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It seems the problem isn't with your AC system but with the cooling system.

A hot car won't let the AC run effectively. How's the coolant level in your vehicle?
 

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Discussion Starter #4
It seems the problem isn't with your AC system but with the cooling system.

A hot car won't let the AC run effectively. How's the coolant level in your vehicle?
Checked that first and it is OK. Car coolant system runs fine without the AC on. Stays right in the middle where it always has...hot day or cold.
 

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Low pressure service (refill) port on pass. firewall with black cap. Green cap in that area would be the evap. emissions test port. ^+1 on a possible cooling system issue.
 

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Discussion Starter #6 (Edited)
Took it to get the juice for the cooling system and it ran flawless. Cool air coming out and no over heating. When I got home, I checked the pressure on the low port and it was 30. At my ambient, it should have been 45 - 55. So I put the 134A in up to 55. Air is colder, so we'll see. I just may replace that clutch plate.
 

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I have to join the others suspecting the cooling system. If your engine starts to run hot/overheat under light load such as turning on the A/C I'd suspect the coolant pump is worn out. Even if your coolant level is fine (not the refrigerant in the A/C system but the antifreeze), if it's not circulating properly any load will cause the engine to run hotter and if the coolant's not getting to the radiator you'll have problems.
 

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Discussion Starter #8
OK..I left home on another 94 degree day. Air conditioner pumping out cold air like it should and engine temp staying right in the middle as always. Up hills...down hills...flat road...stop lights.... high speed...low speed....all the regular driving. No problems. Probably a total of 30 -40 miles of driving, only 160 pounds of scrap metal and an old air conditioner in the trunk that I dumped off at recycling. No problems.

My last 2 miles home, I all of a sudden smelled the smell I get through my vents when the AC is turned off from running. Felt the air and it was warm. Checked the temp and it had gone to "H". Shut off the AC and temp went back to normal after 15 seconds.

I'm starting to think maybe the surpentine belt is worn. It shows no evidence of cracking or wear but it is the original and has 213,000 miles on it. It could be slipping even though I'm getting no squeeling. maybe it's slipping when the AC compressor puts a heavier load on it. As far as the coolant pump is concerned, it's nothing but an impellar that turns and pumps coolant. It either works or doesn't. It either leaks or doesn't. It is noise free telling me the bearing is OK and no leaks. These pumps don't stop pumping, they leak usually through the bearing. Not a drop or rattle to be seen or heard.

Going to change the surpentine belt. If it was the coolant pump, I wouldn't be able to ride all over the place with the AC on in 94 degree weather for 50 miles with no problem.
 

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Discussion Starter #9 (Edited)
I do believe that I have a cooling problem. I don't think it's the coolant pump, but I think maybe old coolant...I hope not a plugged radiator.

Also...is the AC compressor clutch supposed to cycle? Mine seems to run all the time. I read somewhere on the web that if the clutch cycles on and off, it's a sign of low refrigerant.

Anyway, taking it to the Ford Dealer so they can use their flushing machine. Been awhile.
 

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Also...is the AC compressor clutch supposed to cycle? Mine seems to run all the time. I read somewhere on the web that if the clutch cycles on and off, it's a sign of low refrigerant.
Yes, A/C should cycle roughly every 10-20 seconds. Your low pressure switch might not be working. The compressor is probably only turning off when the high pressure limit switch is tripped. Engine overheating will rase the A/C system pressure, so that's probably why you noticed the A/C turning off when the engine was overheating.
 

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Discussion Starter #11
Yes, A/C should cycle roughly every 10-20 seconds. Your low pressure switch might not be working. The compressor is probably only turning off when the high pressure limit switch is tripped. Engine overheating will rase the A/C system pressure, so that's probably why you noticed the A/C turning off when the engine was overheating.
I think I replaced the low pressure switch a couple of years ago and it didn't change the symptom I had at that time...can't remember what it was.

Where is the low pressure switch located on the Duratec AC system.
 

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Discussion Starter #12 (Edited)
Wait, I'm confused here. The low pressure switch is a normaly open switch that closes on pressure (as low as 25 pounds) to supply voltage for the coil to energize and pick up the clutch. It should not open unless you have a low pressure issue that would ruin your compressor. It should always be closed otherwise.

On the other hand, the high pressure switch is normally closed and opens under high pressure. So it seems to me if my clutch was not cycling and always staying energized, it would be the high pressure switch that is not opening to kill the voltage to the clutch coil....not the low pressure switch being stuck. If it was stuck open, the clutch would never energize. If it was stuck closed, it just wouldn't open under a low pressure condition and keep the clutch coil energized.

I don't have a low pressure condition. That switch should always be closed. When the high pressure switch opens, and the clutch drops out, it won't pick up again until the pressure drops low enough for it to close again and supply 12v to the clutch coil.
 

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Discussion Starter #14
I just read on teh Ford truck forum a guy had the same problem. They said the compressor would run almost 100% of the time on hot humid days. That's what I had and that's what I got. Plus the control was on Max Cool which is recirculating the cabin air..blower fan was on full blast and I had the windows wide open. That's why it didn't cycle.
 

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I just read on teh Ford truck forum a guy had the same problem. They said the compressor would run almost 100% of the time on hot humid days. That's what I had and that's what I got. Plus the control was on Max Cool which is recirculating the cabin air..blower fan was on full blast and I had the windows wide open. That's why it didn't cycle.
It should still cycle, even at a much slower rate (but still more often than once per minute). Unless we're talking 100+ degree humid days. You might want to have someone with a manifold set check your pressures. Engine overheating or a blocked condenser will cause the compressor to run nonstop. You should make sure the front of your radiator (actually the condenser coil) is clean and free of debris. Hose it out if you can.
 

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Discussion Starter #16
It should still cycle, even at a much slower rate (but still more often than once per minute). Unless we're talking 100+ degree humid days. You might want to have someone with a manifold set check your pressures. Engine overheating or a blocked condenser will cause the compressor to run nonstop. You should make sure the front of your radiator (actually the condenser coil) is clean and free of debris. Hose it out if you can.
I guess I don't understand what makes the compressor cycle. I've read threads that say it should cycle. I've read threads it shouldn't cycle. I've read threads that say it should cycle when it's really hot and humid and I've read threads that say it shouldn't cycle when hot and humid.

If the low pressure switch opens at 25 pounds and it never sees 25 pounds, the only thing that can make it cycle is the high pressure switch opening, which if I understand it, is a bad thing.

So if someone can explain how a circuit can disconnect when both switches are supposed to remain closed, I'm listening.
 

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High press switch opens to prevent AC comp /system damage if press is too high due to overcharging, plugged lines, etc.

Low press switch controls evaporator core temperature. The pressure of the gas (its a gas after the orifice tube, a liquid before orifice tube) is directly related to the gas temp. As gas temp drops, gas press drops. The low press switch is set to open around 25 psi or so, which corresponds to a gas temp of 35 deg F or so. If core temp drops below 32 F, condensed water on core will freeze, and plug the fins with ice, and result in no air flow thru core and no cooling the car.

Back in the "old days" evap core temp was controlled by a mechanical expansion valve that had a probe stuck in the evap core and mechanically regulated freon flow to keep core from freezing up.

I have monitored AC demand with a scan tool several times in very hot, humid weather (temps high 90s / dew points in the 70s) after starting the car that has been sitting in the sun for hours. AC comp will run continuously for quite a while in the engine is running at low RPM much of the time such as in stop and go driving.

Remember the high and low press switches dont directly power the clutch, but triggers the AC clutch relay which in turn powers up the clutch.
 

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Discussion Starter #18 (Edited)
Did a test. Started car from cold start standing overnight. Outside temp 65..dew point 62. AC on Max Cool...blower fan on high...windows rolled up...doors closed.

Upon engine start up, and turning AC to Max...clutch engaged and was cycling at a rate of 13 seconds on..8 seconds off. fan on my left (condenser coil fan?) facing car running. Air out of vents cold. Engine starts to warm up, I hear a fan come on high (probably engine cooling fan) check engine temp and it is in the middle normal. Notice frosty ice forming on a line next to the fan on the left. Air out of vent is now very cold. Cycling of AC clutch now longer on..about 25 seconds. I continue to run the car in the above condition and check the engine temp...still in the middle as normal, but the clutch has now stopped cycling and is engaged constantly. Engine never overheated. Air out of vent remains very cold.

Insight? Does this sound OK or suspect? Thanks.
 

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Well, it started out normal but then went wrong. You should not ever see frost on the suction line (moisture is okay, just not frozen), because it means the temperature is below freezing, and as Jeff explained that mean the pressure is too low since the two are intertwined. This means that you will be forming ice in the evaporator which will choke off all the airflow and prevent further heat transfer from occurring.

So you definitely need to get it looked at.
 

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Discussion Starter #20
I'm going to try and get my hands on a set of manifold gages and see what the pressures are.
 
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