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Still not happy...

plongson on Tue March 18, 2008 9:49 PM User is offlineView users profile

Year: 1984
Make: jeep
Model: cherokee
Engine Size: 2.8
Refrigerant Type: R-12
Ambient Temp: 70-75
Pressure Low: 10-12
Pressure High: 115-125
Country of Origin: United States

I'm back to r12 and I'm baffeled.
After I charged on Saturday it looked good. The ambient was about 60° and the center register was about 42°-43°. Had a B'day party to give so I had to quit for the day.

Fast forward to today, first day I had opportunity to look closer...center register was 47°

See the numbers above. I'm really looking for high 30's to low 40's center register, with the ambient at +70°.

Here is somemore info.

I charged with about 34oz of R-12. one book says 32oz another says 40oz. WTF...
I clamped off the heater hose so no hot water entered the cab
Doors open on MAX, 1500-1800rpm. Actually went out and ran around before I came home and put on the gauge set.
Sight glass is full when the comp. is running, comp off, liquid drops down in the receiver...comp starts, liquid comes back up.
LP line back to compressor from TXV is frosty at TXV. Cold but not frosty at compressor every cycle. (hose has short piece of alum. tubing on both ends)
Sprayed condenser with water to look for dramatic pressure drop. Not too dramatic, lowest was about 100psi
New clutch on fan. Seems to be moving a shit load of air.
Clutch cycle time seems OK. On for about 30-40 sec. off for about 20. (didn't time it, this is from memory)
Just about the time things start to get cold it seems the clutch drops out and the temp goes up.

So whadd'a ya think...

Low charge?
Bad pressure switch?
Normal operation parameters? Leave it alone.

I'm lost...

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Vibration Analyst in Power Generation

Edited: Thu March 20, 2008 at 10:14 AM by plongson

Chick on Tue March 18, 2008 10:13 PM User is offlineView users profile

Sight glass clear, suction line cold back to the compressor? without hosing the condenser? pressures look a little low, are they without wetting the condenser? Remember the hotter it gets, the longer the compressor will stay on, but you may be a couple ounces low..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

TRB on Tue March 18, 2008 10:24 PM User is offlineView users profile

CJ Series = 40oz

Cherokee/Comanche = 32oz

I never liked the cooling on these vehicles. Pressures seem low even at that ambient.

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When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

mk378 on Tue March 18, 2008 10:36 PM User is offline

Since it's a TXV system, there should be a temperature control switch on the evaporator. Once the vent temps are down to where that control starts to cycle, you can try whatever you want under the hood to improve the performance of the refrigerant loop. But it will be to no avail because the evaporator thermostat will just cycle the compressor off more.

plongson on Wed March 19, 2008 10:33 AM User is offlineView users profile

I found and attached a print that has the aforementioned thermostat switch. Is it attached solidly to the evaporator or is it located within the duct assembly?
I’m seeing a mess of wiring behind the louvers in the center register that are accessable...It would be nice if it was that easy to get to. If not, there's no way I'm tearing into the dash.

So this switch is what actually controls the compressor cycle rate?
Are there any other components involved?
Can I energize the clutch to test the system, what are the risks?

CHICK: (Sight glass clear, suction line cold back to the compressor? without hosing the condenser? pressures look a little low, are they without wetting the condenser? Remember the hotter it gets, the longer the compressor will stay on, but you may be a couple ounces low.. )

1.) Yes, sightglass is clear, no bubbles at all. When comp stops, liquid hesitates for a moment then drops into the receiver.
2.) High Side pressures: Dry condenser,125lbs. Wet condenser, +/-102lbs
3.) Suction line frosty at TXV, but mostly just sweaty on the other end. (some cycles it will frost, sometimes not).

I love this stuff but what a PITA…

Paul…



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Vibration Analyst in Power Generation

Edited: Wed March 19, 2008 at 4:12 PM by plongson

bohica2xo on Wed March 19, 2008 8:15 PM User is offline

P.

Out here in the desert, you can get away with somewhat lower evaporator temps than other places. I run low 30's without issues when the RH is below 15%.

You will not hurt anything by letting the evaporator ice up a little during testing. You can feed +12v to #2 terminal of the low pressure switch for testing. Put a jumper on it and go for a drive, I suspect you will see vent temps below freezing. Of course once the evaporator ices up, the airflow will drop off...

I run a pair of cycling switches on a CCOT system, and let one dip down to 13 psi when it is hot & dry. I ran an override time delay on another system, letting the low pressure drop uncontrolled for the first 6 minutes after system start - that helped pulldown as well.

You could adjust your low pressure switch up a bit, and provide a shunt across the thermostat switch for reduced vent temps when needed. A time delay or just a manual switch would work.

I suspect the factory setting is probably the 42~43 degrees you are seeing, which would prevent freezing in any climate. One size fits all...

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

mhfd112 on Wed March 19, 2008 9:32 PM User is offline

If the ambient was 60 I think I would leave it as is and see what it does on a warmer day.

plongson on Thu March 20, 2008 10:08 AM User is offlineView users profile

Tomorrow is suppose to be a nice warm day (mid 70's) and I'm off, so that will give me a chance to play with it somemore.

I need to determine what switch is opening up, the thermo or the low pressure to get to the root of this.

What PSI should I expect the LP switch to open at??
I saw it as low as 10psi the other day when the ambient was 60°f

If I still cannot ge the temps down, could it be low on refrigerant?
Should I expect the suction line to frost all the way to the compressor before it cycles off?
Should the liquid drop down into the dryer when it cycles off?
All suggestions on tweeking R-12 are ALWAYS greatly appreciated!! LOL

I am getting my ducks in order before I jump in again.
I'll be sure to let you know what I find.

THANKS!!!

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Vibration Analyst in Power Generation

Edited: Thu March 20, 2008 at 10:17 AM by plongson

mk378 on Thu March 20, 2008 10:53 AM User is offline

On most TXV systems, the low pressure switch is detecting pressure somewhere on the high side. It will only open in case there has been a near total loss of the refrigerant. It's normal for low sides to drop quite low in cool weather. Thus the switch is on the high side so it stays always closed in normal operation. Check your Jeep to see if this is the case.

plongson on Thu March 20, 2008 5:40 PM User is offlineView users profile

DUH!!
Your right, I didn't think of that. The LP switch is on the HS.
Glad you mentioned it though, because I had it in my mind that LP witch could be part of the problem. You just saved me some brain cells...

BOHICA has me thinking though...If I have a funky thermo switch shutting me down too soon, I might put in a toggle switch to override.

Might seem like a bastard deal but we ain't dealing with a new Mercedes Benz. I'm probably the last owner this little bucket will have anyway. Just cause' I love it doesn't mean anyone else will...LOL

I'm still wondering about the charge, the temp of the return and liquid level in the sight glass.

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Vibration Analyst in Power Generation

Edited: Thu March 20, 2008 at 5:54 PM by plongson

bohica2xo on Thu March 20, 2008 9:15 PM User is offline

P.

Sorry, I was not thinking about where the LP switch might be located - with Jeep you never know... You can find 3 different fan / belt / alternator combos in the same model year on the I6.

Since your switch is located on the high side, you will need to limit the time you shunt the thermal control. It will ice up eventually, especially at lower fan speeds. Perhaps using a relay in the shunt circuit that is tied to the highest blower speed would do the trick.

As far as the charge level, the sightglass shows the minmum charge. A couple of ounces past clear is the maximum charge. When the clutch cycles off, the refrigerant continues to flow across the TXV until the receiver is empty - so you see it drop when the compressor cycles off.

The return line should be cold, and frost is not an issue at that low ambient. When it is 110f ambient you will not see much frost underhood.

Your refrigerant loop looks ok, pressures are low because of the ambient. It should hit 80f here by monday, you will see some higher pressures then.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

plongson on Thu March 20, 2008 9:35 PM User is offlineView users profile

Check this out. Still trying to cover all the bases...


75° ambient
1.) I found the heater valve to be NFG and replaced it. Probably stops the coolant much better than "C" clamps...(ya think)
2.) Fired it up and jumped out the clutch. Fan on high and the doord open. The SOB pulled down to 34° (wetting the condenser) before I pulled the jumper! I plugged back in the clutch to let the thermo switch do its thing. Actually pulled down to 39.5 but dosen't pull back in until about 48°f and it only takes a second to climb right up there.

SO...It looks like the charge is good and the problem was a bad heater valve AND I still have to figure out what to do about the Thermo switch. I'm going to drive it tomorrow and see how it goes. I might just live with it...I might throw in a toggle. We'll see...

Here is the thermometer/meter I use. I believe its pretty accurate for this application and the wind speed and RH options are nice.

Kestrel

I'll let you know how it goes tomorrow just for kicks...

PS...I just want to say THANK YOU again to EVERYONE that helped me here...again. This is a great site and a great source of information. And just so you know, I have passed on this site and recommended ACkits to my friends that need parts. The internet is full of liars and BS and it is really nice to find a place filled with honesty.

Thanks Tim for the site.

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Vibration Analyst in Power Generation

Edited: Fri March 21, 2008 at 10:52 AM by plongson

bohica2xo on Fri March 21, 2008 2:23 PM User is offline

P.

Well there is your answer. You have more cooling power than you thought you had. Even in higher ambients, with a good road speed it is possible to freeze your evaporator.

The hysteresis in the freezestat has been an issue for me for a long time. On older Saab 900's the factory manual advised adlusting the cut IN temperature, rather than the cut out. This allowd the evaporator to rise above 0c long enough to shed ice, but not long enough for the air from the vents to "go warm" and generate a customer complaint.

Somewhere along the way engineers decided that a "no freeze" setting was somehow better. It may be because of the so called world market. Here in the southwest you usually have 90f+ inlet air to throw at the evaporator, so if it spends some time below freezing and some above it does not accumulate ice.

I try to use 36f to 40f as a cut IN temperature, even if the cut out falls as far as 25f. I know replacing that thermostat is probably not high on your list, and it is not a five minute job. If you do use a manual switch, consider a time delay relay or the electronic equal to limit the time you shunt the thermostat. Put your jumper on, and go for a five minute drive, you will be amazed.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

plongson on Fri March 21, 2008 5:58 PM User is offlineView users profile

Thanks B.

Well, here it is the day after...This thing pretty much rocks in this weather. Ran around today and its pretty impressive. Center register will freeze your butt off. I'm going to skip the override for now, but if it needs it later on...who knows.

You guys always recommend "check the blend doors and heater valve". I cannot emphasize how important that is after seeing how just a small amount of hot water can screw you. Its just like having the system on max cool with the temp turned up.

After running both 12 and 134, I agree that a system designed for 12 should stay with 12. It really seems much happier.

Anyway, we're "Chill'n" now.

Guess I'm off on another project...

Thanks again!

-------------------------
Vibration Analyst in Power Generation

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