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Discussion Starter · #1 ·
Here's one I haven't seen in a year of searching the web. All you AC geeks can get tested.

Static pressure ~ 70 at 82 degrees ambient.
While operating High pressure is 220, low is 30 @ ambient 82.

I had my hoses hooked up and running the above pressures when the compressor clutch suddenly disengages and does not reingage for 20 minutes before I shut the car off and gave up

Background:

AC works great if abient temp is less than 80. Works all day long.

When ambient temp hits 85 to 90, AC works great for 10 to 15 minutes then compressor disengages for about 30 seconds, then works for 3 more minutes, then compressor disengages for 30 seconds, then works 2 minutes, then compressor stops for 30 seconds, then works for 1 minute, then compressor disengages and will NOT come back on.

Sometimes I can cut the AC off and wait 5 to 10 minutes and it'll come back on. Sometimes it will never come back on.

How long it the AC works depends on the ambient temperature. Don't think the Evaporator is freezing up ... there is no change in air flow in the vents.

Thought perhaps the low pressure switch is going bad, so I waited for the compressor to refuese to engage and jumped the low pressure switch. Nothing happened.

Thought the relay might be bad, so I jumped the AC clutch relay. Nothing happened.

I checked the voltage across the AC clutch relay contacts, and its 12 volts. Turned AC off and the voltage across the relay contacts is 0.3V. Checked the voltage across the relay sensor contacts and its also 12 volts when the ac is on. So, I'm confident that the sensor is telling the relay to engage, and because I jumped the relay and it still doesn't engage, the relay is good and it must be something else.

Could the clutch coil be going bad (clutch gap) and when it gets hot enough it refuses to work?

Checking rockauto.com I found there are several sensors. There is an ambient air sensor (I don't think that's got anything to do with it). There's an AC Compressor relay, but I think that's the same as the AC Clutch Relay. IF not, I don't know where it is. There's a AC low pressure switch that I've jumped and makes no difference. There's a binary pressure switch that I have no clue what it does or where it is.

HELP!!! I'm at my wits end. I have not tried to jump the coil contacts yet. How do I even do that without frying something.

IS t just that my AC clutch has worn enough that when it gets hot enough it won't engage?
 

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IS t just that my AC clutch has worn enough that when it gets hot enough it won't engage?
Could very well be.
I didn't see a mention of the mileage, but A/C clutch surfaces do wear. High under hood temperatures exacerbate the problem, allowing the clutch surfaces to migrate apart from each other. During the next failure, check for magnetism at the clutch surfaces.

If you have magnetism, then you have power and ground.

By removing a shim, you can reduce the clutch gap, which will allow the compressor to engage regardless of under hood temps.




Of course replacing the clutch (with a new one) would accomplish the same thing.
 

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When the clutch refuses to engage lightly tap the clutch shoe plate with a screwdriver handle - be very careful not to get your hands,clothing,tools tangled in belts or fan. If the clutch engages you have a clutch gap too wide. Spec is 0.014-0.033 inch. Coils sometimes do have problems as they heat up. Also check the voltage at the clutch coil connector it must be 12 volts or more. Attached a schematic in pdf.
 

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Discussion Starter · #4 ·
Thanks for the quick response. Mileage is 160k. I wouldn't have thought the clutch gap would be so sensitive that a few degrees would cause a malfunction. I'm still not convinced that's the problem.

I had decided to remove the splash gaurd and come at it from the bottom .. which means I'll have to pull it up on ramps. You have to be a contortionists to work on this car.

1) Immediately after turning on the AC,I'll check the voltage across the coil connectors either with it connected, or the wiring after it is disconnected to get the "proper" reading. Then I'll check is again after the clutch refuses to engage. If the voltage is correct after it refuses to engage, I'll try and jump it. If it still doesn't engage, its got to be the clutch or clutch coil.

2) After it refuses to engage, tap on the clutch to see if it will engage.

3) If voltage is improper, while it is refusing to engage and there is a 12v across the relay, then its another electrical problem. But I'm running out of possibilities.
 

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There can be a break in the winding of the clutch coil that is separated when the coil gets hot and the winding expands. The coil is a strong electromagnet and it can be checked for magnatism by applying battery voltage to it. Check it when the clutch is working and when it is not working. The clutch gap is important but not all that sensative. IIR some Fords call for .027 to .075 as the gap perameters, but most are usually set at about .035.
 

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I'm no A/C expert so I had to go borrow info from CEG but, according to this link, it sounds as though your high side may be well, high.

A/C problems continue

Also, I didn't see that you posted which engine you have, not sure if that will make any difference, how ever the link above appears to be for a Zetec).

I noticed I started having problems with my air working intermittently on my 95 w\Zetec, it would work great, then not. Similar to what you are describing when my compressor started to go, then it went and took the serpentine belt with it.
 

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Discussion Starter · #7 · (Edited)
I'll be checking the clutch and clutch coil this weekend, however

2.0 engine.

I had gages hooked up reading 30 low side and 220 high side when it just stopped and would not kick back on. (I also suspect I"m a tad low on freon) Thus, I don't think my high side is too high. this has been going on for over a year. If the compressor was starting to go bad, it would have failed by now.

I'm 95% sure its either the clutch gap, clutch coil, or bad connection (ground or power) to the clutch coil.

Acker, I read the other thread. I think the fan problem caused the compressor failure. The fan should always be on when the compressor is on.

I'ver heard AC guys say that as compressors go bad, the will not cool as well after they warm up because the reed valves expand and don't compress well. My ac is great IF the compressor runs.
 

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Discussion Starter · #8 ·
Followup: I think its fixed.

Pulled the tire and plastic fender guard to get to the compressor. This thing is very poorly laid out. I could barely see the electrical connection on the compressor, much less get to it to remove it. I had to press on the connection with a 24" screwdriver, while pulling up on the retainer clip with a 180 degree bend in the end of a coat hanger just to get the connection off. I was afraid I was going to break the retaining clip off of the electrical connetor. Otherwise, I couldn't get it off without pulling the compressor. What moron designed that system?

Anyway. I checked the voltage at the compressor wiring. It showed 12V. I pulled one shim out of the clutch gap to decrease the gap.

It appears to have done the trick. The compressor no longer refuses to kick in after 15 minutes when the temperature is over 90. Apparently, as the clutch heats up, it bows outward that effectively increases the clutch gap beyond the coil's capability to pull in in. Go figure.

Next issue: I am short cyling. I think its overcharged. Running at 1500 to 2000 rpm, it will freeze you out and stay engaged. Running high rpms (3000 at 80 mph like I like to run) it short cycles. Clutch will engage about five seconds, then disengage about 5 seconds.

Pressures:

90 degree ambient. Condenser 130 degrees. Engine ~ 1500 rpm

Low side 28 psi
High side 280 to 300 psi.

I think that's indicative of on overcharge. Please confirm. I may have too much oil in it.

Questions: If the system leaks down to 10 psi static pressure, does the oil stay in the compressor? Do you need to put more oil in when you recharge if the system leaks down? I did. If you evacuate the system while running the compressor, are you getting all the oil too? If you evacuate without the AC on, will it leave the oil in the compressor? Will pulling a vacuum get the oil out just like it does the moisture? If the answer to all of this is no, how do you get all the oil out of the compressor for a clean recharge without pulling the compressor and draining it out by hand.

Thanks for all the help guys.
 

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General notes;
The "ambient temperature" refers to the under the hood temperature that the A/C system is operating in. You need specific information on the refrigerant oil in a specific system. In general there is about 1 to 1.5 ounces in the condenser, an ounce in each line, an ounce in the accumulator (filter/dryer), and an ounce in the evaporator core. The total amount of refrigerant oil in the system is usually about 7 to 7.5 ounces. The ONLY way to change oil in the compressor is to remove it, carefully, and drain it into a measuring container. The amount removed should be the amount replaced in the compressor. If the condenser is replaced, or removed and cleaned you put the factory recommended amount of oil in the new/clean condenser. The same goes for the other aforementioned A/C components. This is rarely needed unless there is a failure like the "black death" of the compressor. The whole system would be contaminated and need the kind of cleaning and fresh oil you are talking about. Check your pressures against the factory chart and the various "ambient temperatures". 30 psi to 50 psi on the low side, and 200 psi to 250 psi on the high side is not unusual. If you think you overcharged the system you can properly evacuate a little refrigerant and see if the pressures settle down.
Note that the refrigerant oil is very fine and it becomes a mist and flows throughout the system with the refrigerant. (FREON is a DuPont tradename for their refrigerant) The oil gets deposited throughout the system and the amounts in each component will vary slightly. See a good service manual for the details for your make and model year.
 

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Discussion Starter · #10 ·
Thanks, Hawk. So, if I connect my gages and evacuate

the 134a (freon is easier to type) when the car is cold, not running, and has sat overnight, do I also remove my oil?

My answer would be no, but I don't really know.

I think if I evacuated it while running, much of the oil would also be removed. Will all of it be removed?

I'm pushing 300 psi high and 28 low at 90 degrees and 1500 to 2000 rpm (I don't have a tach). I want to remove some to see if my high side decreases without lowering my low side.
 

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Technically you must "capture" any refrigerant you remove from the system. I would only worry about adding oil to the system if there has been a significant oil leak. There are special tools for injecting oil into the A/C low side port without loosing any rerfrigerant. Evacuating (capturing) a few ounces of refrigerant from the system is not going to cause any significant oil loss.
What are your pressure readings at idle and at normal operating temperiture?
 

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Discussion Starter · #12 ·
I'll check pressures again this weekend, but last check

ambient 90 degrees, Condenser=135 degrees, Idle,

Low=28, High=250

~2000 rpm (I don't have a tach)
low-28, High = 300

The high reading makes me think I've got an overcharge. The unit cools well, but short cyles.

It leaked all out (leaking high and low pressure ports) last summer. I replaced both ports, put in 6 oz of oil, and about 24 oz of 134a. I then fixed the clutch gap and it works well, but short cycles. Works better when running about 50 mph (~2500 rpm).

I want to completely drain all refrigerant and properly recharge using th gage readings. I will not be pulling a vacuum or flushing. Do I add oil?

Two questions:

1) do those pressure readings indicate overcharge.

2) Do I add oil back upon recharging? I think not because I think the oil will stay in the system when I capture the 134a under with the engine off (static). Oil is not a vapor in the static condition. Please confirm.

Thanks
 
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