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AC Compressor Fast Cycles When Hot Outside (90+)

jbelcourt on Sun September 13, 2015 12:18 PM User is offline

Year: 1993
Make: Lincoln
Model: Mark VIII
Engine Size: 4.6L
Refrigerant Type: R-134a

**I apologize in advance as this will be long. I want to be honest about what I did and did not do, and how I did it, to better diagnose this issue**

So, I rebuilt the AC on my car a few months ago because the old compressor ravaged the system (full of black sludge type stuff and metal). All parts were NEW (not reman) and I did not buy any "fake" no name brand parts from eBay. The only major component that was not replaced was the evaporator core due to the work required (removing the dash is an absolute pain in these cars!) but it was flushed using Denatured Alcohol and shop air. I do not own manifold gauges or a vacuum so I rented those from AutoZone for the work to be completed.

Parts used:

Spectra Condenser
Four Seasons Accumulator
Global Discharge Hose
Four Seasons (FS10) Compressor
Variable Orifice Tube from O'Reilly (stock is fixed orifice)
R-134a cans from Wal-Mart (store brand)

First part of being honest and admitted something I did wrong. I rebuilt the entire system, pre-oiled the compressor (added UV dye), primed it to ensure no instant death and set up to pull vacuum. I realized I left the metal "retaining" clips at home so I set up the vacuum and left to go pick them up from home and eat dinner. I let it run for about 2 hours by the time I got back. Shut it off and it wasn't holding (slow leak down). At this point it was already 10:00 at night and my car was in the storage bay at work and I couldn't see hardly at all. I pulled a few lines off to check the o'rings and they were all fine. Tried pulling vacuum again and still leaking. I got frustrated and decided to just attempt to give it the first charge and look for the leak that way (since I had dye in the system).

Started up, it took the first can perfectly, got the second and then the compressor started cycling. AC got nice and cold (yay!) and I was trying to find the leak. I had my brother next to the accumulator and I was watching the compressor. Couldn't figure it out. Got it fully charged, shut the car off and realized the accumulator was leaking pretty obviously at the pressure switch (thanks for noticing that obvious one little brother!) so I pulled it off and installed an o-ring. Leak fixed! That being said, I did not establish a proper vacuum due to locating the leak via that method.

AC worked great. Ice cold (though it could and probably should be slightly colder.....if I remember correctly it was reading about 43-46 degrees but humidity was pretty high as I'm in Florida and it was July) and no obvious issues.

I started noticing that when it's really hot outside (it's Florida so I guess it's always hot), like 88+, I'd start the car, kick the AC on and the AC would get instantly cold but then the compressor would cycle and the air would be "cool" at best. Then it'd cycle back on, ice cold, then back to cool. All within probably 5 seconds or so, approximately. Most of the time, if I drive it and try and get those RPMs up high real quick, within maybe 5-10 minutes it'll stop and work fine...though sometimes it'll keep doing it and I just turn it off as to not strain my new compressor.

In the mornings, or when it's "cool" outside (mid-80's) she works great. This ONLY happens, like I said, when it's 88+. I'm trying to figure this out as it's driving me crazy.

I'm not above bringing it to a professional at this stage to have the refrigerant properly balanced, as maybe I'm just slightly off (and I know how precises you have to be with AC systems) but I'd rather do my best job troubleshooting it first before going that route.

When I checked the levels, they were within specs (I can't remember the exact numbers but I checked them against the shop manual a friend supplied me) MAYBE ever so slightly high. I've never checked them while this issue was occurring as I don't have gauges and I'd have to go rent some.

My thoughts are:

Bad high or low pressure switch (I did not change those)
Blockage of the orifice tube (though I don't think this is the issue, I haven't ruled it out)
Unbalanced pressures
Moisture in the system (due to not pulling a proper vacuum)



Any insight would be greatly appreciated. I'm all ears and I'm willing to take anything reasonable into consideration and I can provide any addition information you may need.

Thank you.

-Jamie

mk378 on Sun September 13, 2015 2:51 PM User is offline

Is this a conversion or was the car factory 134a?

No one here has had good results with the variable tubes-- use stock fixed one or possibly one size smaller if converting.

The first step in diagnosis is to get gauges and watch the pressures-- under conditions where it is NOT working.

There's no such thing as "balancing the pressures". To be sure of a proper charge you start from empty (vacuum) and measure the refrigerant in by weight. This is easy if it is factory 134a so you have the specification. On a conversion you try to use close to, but not over, the specified ounces for R-12.

Edited: Sun September 13, 2015 at 2:58 PM by mk378

jbelcourt on Sun September 13, 2015 3:02 PM User is offline

Quote
Originally posted by: mk378
Is this a conversion or was the car factory 134a?



No one here has had good results with the variable tubes-- use stock fixed one or possibly one size smaller if converting.



The first step in diagnosis is to get gauges and watch the pressures-- under conditions where it is NOT working.

It's stock 134a, it was not converted. I had a fixed tube but several guys in the enthusiast community I'm on in hot regions like Arizona use the variable tubes with good results so I gave it a shot when I did the rebuild.

I'll need to rent gauges again and try checking it after car has been parked at work all day and it's really hot outside like usual.

If the pressure are high, having the refrigerant reclaimed, change to a fixed tube and have it professionally filled would be my best bet I would assume?

If we were to pretend the pressure are good, what could be other possibilities for something like this to happen?

We can rule out the control unit itself because I just switched that last week. My AC could be off and it would literally turn itself on to defrost randomly but display as if it was off and wouldn't respond to any buttons unless I turned my car off and back on. Scared the heck out of me the first time. Possessed AC LOL.

mk378 on Sun September 13, 2015 3:07 PM User is offline

My wild guess based on what you have said so far is that the fan clutch is worn out and the condenser overheats when the car is stopped or moving slow in hot weather. This will cause the high side to go up until the high pressure cutoff trips (about 450) and then cycle back on in a few seconds. Easily confirmed with a gauge. If it always cools well when the car is moving fast enough to force air through the condenser, you may not need to do anything with the refrigeration system, just fix the air flow.

Edited: Sun September 13, 2015 at 3:08 PM by mk378

jbelcourt on Sun September 13, 2015 3:22 PM User is offline

I'll check it out but I'm pretty sure the fan is fine. It's one of, if not the, highest CFM fans out there and is widely used on other cars due to that. It's definitely kicking on high like it's suppose to. Plus, once it stops acting up and the ac starts working fine, it doesn't matter if I'm moving or stopped, it's working fine.

I appreciate the information regardless and I'll check the fan since it was suggested. I'll have to see if I can rent gauges again, or just buy a cheap set from Harbor Freight to have on hand.

It's driving me crazy though lol.

Edited: Sun September 13, 2015 at 3:23 PM by jbelcourt

HECAT on Mon September 14, 2015 1:26 PM User is offline

Quote
Originally posted by: jbelcourt

If we were to pretend the pressure are good, what could be other possibilities for something like this to happen?

You stated you checked the levels and they were within spec. You cannot make this false assumption; you are correlating charge and pressures incorrectly. The "level" is a specific volume of refrigerant that can only be measured precisely by weight. System performance is measured by pressures. If the charge level is off, other issues can come into play that do often produce "false-good" pressure numbers. Without first verifying proper charge by weight into a good vacuum; this can and will send you on a pretend wild goose chase.

The poor vacuum issue, one can in, two can in, got it fully charged, had a leak, fixed the leak; all indicate to me that we really do not know where the charge level (weight) is. Erratic system operation could be normal cycling on the (HP or LP) pressure switches, and effected by ambient temps. I would recommend before chasing your tail any further; the system should be recovered, put a OE OT in it, vacuum, and recharged by weight to spec. Then get some gauges on it and report what pressures and problems you have.



-------------------------


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jbelcourt on Mon September 14, 2015 7:31 PM User is offline

Quote
Originally posted by: HECAT
Quote
Originally posted by: jbelcourt


If we were to pretend the pressure are good, what could be other possibilities for something like this to happen?



You stated you checked the levels and they were within spec. You cannot make this false assumption; you are correlating charge and pressures incorrectly. The "level" is a specific volume of refrigerant that can only be measured precisely by weight. System performance is measured by pressures. If the charge level is off, other issues can come into play that do often produce "false-good" pressure numbers. Without first verifying proper charge by weight into a good vacuum; this can and will send you on a pretend wild goose chase.



The poor vacuum issue, one can in, two can in, got it fully charged, had a leak, fixed the leak; all indicate to me that we really do not know where the charge level (weight) is. Erratic system operation could be normal cycling on the (HP or LP) pressure switches, and effected by ambient temps. I would recommend before chasing your tail any further; the system should be recovered, put a OE OT in it, vacuum, and recharged by weight to spec. Then get some gauges on it and report what pressures and problems you have.

This is basically where I felt like I was at anyway, I figured I should ask first in case I was overlooking something.

I don't have access to a recovery system so I'll have to do what I was thinking about doing anyway and just take it to a shop, have them recover it and fill it themselves.

My system calls for 34 oz and each can is 12 oz. From what I was told, you never get the full 12 oz from the can and should expect a loss of approximately 1 oz per can. Going on that, I charged it with 3 cans which should have set me at about 33 oz. Even if all three cans emptied (which is impossible because each one had discharge when I disconnected the adapter to switch cans) that would put me over by 2 oz. Of course, during the charge process, I had a small leak as I stated. So realistically, my system is currently holding between 30-36 oz. With as precise as these system have to be, I understand what you're saying.


I think what I'm kind of hoping to find out is that it's not anything else (ie orifice blockage, pressure switches, etc) before I go and pay someone else to correct my charge. I did the entire rebuild myself, which saved me a LOT of money, and I should have swallowed my pride and got it professionally charged to be safe.

Thank you for your input, I appreciate that.

mk378 on Mon September 14, 2015 7:44 PM User is offline

You haven't said much about oil. The proper amount of oil is important. Too much and you have excessive pressure. To little, of course, leads to compressor seize-up. Store compressors usually come full of oil because they don't want to have to warranty it if the installer doesn't bother to add oil.

jbelcourt on Mon September 14, 2015 9:40 PM User is offline

Quote
Originally posted by: mk378
You haven't said much about oil. The proper amount of oil is important. Too much and you have excessive pressure. To little, of course, leads to compressor seize-up. Store compressors usually come full of oil because they don't want to have to warranty it if the installer doesn't bother to add oil.

I completely drained it of the shipped oil, just to play it safe (though it didn't have much at all...less then an oz) and I filled it to shop manual capacity...which I believe was 7 oz....with PAG46 Low Viscosity oil.

If it were slightly high on oil, would that only cause excessive pressure during "extreme" heat conditions though?

Dougflas on Tue September 15, 2015 8:52 AM User is offline

If you have too much oil, you will lose cooling capacity. As mentioned, variable OT are not usually good to use. Theonly time I have heard one work was for a mail crrying jeep which was slow speed and stop and go.

Dougflas on Tue September 15, 2015 8:52 AM User is offline

If you have too much oil, you will lose cooling capacity. As mentioned, variable OT are not usually good to use. Theonly time I have heard one work was for a mail crrying jeep which was slow speed and stop and go.

jbelcourt on Tue September 15, 2015 8:09 PM User is offline

Quote
Originally posted by: Dougflas
If you have too much oil, you will lose cooling capacity. As mentioned, variable OT are not usually good to use. Theonly time I have heard one work was for a mail crrying jeep which was slow speed and stop and go.

I do 90% city driving (Orlando Florida) which is why I decided to try the variable OT. I have a stock one here, whenever I take this to get drained, I'll probably swap it out again then.

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