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Pressure cycling switch Pages: 12Last

rm32644 on Wed November 19, 2008 10:33 AM User is offlineView users profile

Year: 2003
Make: Ford
Model: Taurus
Engine Size: 3.0 V6
Refrigerant Type: r134a
Ambient Temp: 50F
Pressure Low: 10
Pressure High: 150
Country of Origin: United States

On this car, the evaporator freezes up after an hour or two on the road. I am assuming since the pressure goes down to 10 psi, the low side pressure cycling switch is the problem. Do I have to evacuate the system and recharge it to install this pressure switch? It is located on the accumulator, and assessable. Thanks for any help

TRB on Wed November 19, 2008 12:03 PM User is offlineView users profile

Should have a valve core under the switch.

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mk378 on Wed November 19, 2008 1:30 PM User is offline

If it's a 2 wire switch, make sure the compressor actually drops out when you unplug the switch. If it doesn't, there's another problem.

I think they all have a valve under the switch that closes when you start to unscrew it. Replace and lubricate the o-ring, and after putting the new switch on, check for leaks from the switch or the o-ring.

Chick on Wed November 19, 2008 4:00 PM User is offlineView users profile

Yes, they have a shrader valve under the cycling switch, but as mk378 stated, watch the pressure and then unplug the switch when the pressure drops to around 20 or 25psi to make sure it shuts the compressor.. It's a two wire switch and as stated, lube the new O ring and don't over tighten as they can crack (Plastic)
Hope this helps....

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

rm32644 on Wed November 19, 2008 4:43 PM User is offlineView users profile

All helpful comments, thanks. I'll do as you guys instructed and get back to you on if this is the fix.

rm32644 on Wed November 19, 2008 10:03 PM User is offlineView users profile

You guys were right about the Schrader valve under the cycling switch. That was good news, no recharging. Well darn it, Advanced Auto sold me the wrong pressure sensor. It looks just like the right one, but it is for a slightly smaller Schrader valve. Ironically the switch side is correct. They felt bad and promise to have the correct one by 9:30 tomorrow morning. The part is what is listed on their parts listing for an 03 Taurus, but it's different. (Always something to make an easy job hard). What's a little scary is the wrong one they gave said it was on at 1.69 kg/cm2, and off at .73 kg/cm2. If my pressure units conversion is correct, that's a range of 24 psi to 10 psi, which sounds too low. I can't image a car that works in that range. Hopefully the correct one will have a more normal range.

Edited: Wed November 19, 2008 at 10:07 PM by rm32644

Chick on Wed November 19, 2008 11:23 PM User is offlineView users profile

Yours should cycle off at around 19 t0 21psi...Hope this helps..

-------------------------
Chick
Email: Chick

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

Freedoms just another word for nothing left to lose

mk378 on Thu November 20, 2008 7:35 AM User is offline

Every time someone specifies a pressure in "kg/cm2", the inventors of the metric system must roll over in their graves. Kilograms are not units of force.

CCOT switches should cut off around 20 psig and back on around 45 psig. The wrong one you have may be intended for TXV systems where it would only be called upon to turn off to protect the compressor in case of a total loss of refrigerant.

rm32644 on Thu November 20, 2008 9:18 AM User is offlineView users profile

Chick,

You must be an engineer too, yeah mass/unit area for pressure is an abuse of the metric system. I notice one good feature of the KG(force)/cm2 is that it's within 3% of being bars, or atmospheres. Like one atmosphere, 14.7 psi is 1.03 kg/cm2, thus you can get a feel for the number quickly.

rm32644 on Thu November 20, 2008 6:43 PM User is offlineView users profile

OK, we bought a new low pressure cycling switch from the Ford Dealer. The one that was freezing the evaporator measured a low end of the cycling at 10 psi. I brought my gages with me, we installed the new one at the dealer, and it is going down to 13 psi on the low end of the cycle. The parts man didn't know anything about the specification of the part. I have to assume at this point that the part is correct, it came up from the part number of the original one in the car, and is for a 2003 Taurus.

I was expecting that a new one would be closer to 20 psi. The low pressure switch is located on the accumulator, which is located at the front of the engine compartment, next to the radiator, on the passenger side. Of course I don't know if this new switch is going to fix the problem, since it takes at least an hour of highway driving for the evaporator to freeze up.

Any comments are welcome.

mk378 on Thu November 20, 2008 10:10 PM User is offline

Looking further, this is not your typical bare-bones CCOT system. Alldata says that car uses an evaporator temperature sensor to prevent evaporator icing. The function of the pressure switch on the accumulator may be only to protect against loss of refrigerant.

The sensor is read by the PCM, not the climate control panel.

If you still get icing (and likely you will), scan the PCM and see if you have a code P1436 or P1437. These codes probably won't activate the check engine light.

Chick on Thu November 20, 2008 10:26 PM User is offlineView users profile

Is this a manual ac system, or auto.. Are you sure your gauges are correct, might want to try another set to be sure...

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Chick
Email: Chick

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

Freedoms just another word for nothing left to lose

TRB on Thu November 20, 2008 11:42 PM User is offlineView users profile

Also make sure you the correct refrigerant level in the system. Being low on refrigerant can cause misleading test results.

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

rm32644 on Fri November 21, 2008 9:46 AM User is offlineView users profile

"PCM and see if you have a code P1436 or P1437", Thanks, we have access to a free OBD II, so we will check for those codes.

Just a comment, where I am measuring the suction pressure (first it was 10 psi now 13 psi at cycle bottom) it is tight into the firewall close to the evaporator. The pressure switch is about 2.5 foot downstream on the accumulator at the front of the engine compartment. I am trying to think of a way that the accumulator could be about 7-10 psi higher than the evaporator out location, but I can't logic that out. In other words, what I am measuring may not be exactly what the cycling switch is controlling at, but it doesn't seem logical to me that the pressure would get higher in the direction of flow.

rm32644 on Sat November 22, 2008 11:39 AM User is offlineView users profile

Note I changed my icon to my 2000 Mustang. (460 hp, Kenne Belle supercharger with intercooler).

Anyway, we hooked up an OBD II to the Taurus this morning, and got no codes. I'm thinking that the cycling switch they sold us at the dealer, which is definitely different by 3 psi than the one we had, is defective, it should be higher. Or my suction gage is wrong, but it does read the same as the high side gage on a equalized system. I will check my gage this morning.

mk378 on Sat November 22, 2008 12:25 PM User is offline

I don't think this system is intended to primarily cycle on pressure. The lower pressure setting of the switch may be intentional, as there is an evaporator temperature sensor too.

Measure your vent temperature with the dial set for maximum cold (not that you'd actually drive that way in 50 degree weather). The evaporator temperature sensor should be turning off the compressor when the evaporator outlet air gets much below 40, regardless of pressure.

TRB has an excellent point. I could see how an undercharge of a system like this could cause a slow freeze-up in cool weather. The part of the evaporator that still gets liquid refrigerant would get very cold and freeze. Then since that part is no longer losing heat, the refrigerant would move further into the evaporator and freeze more of it. Meanwhile since some inlet air is not being cooled at all, the sensor in the airstream doesn't notice. In hot weather you would notice insufficent cooling.

rm32644 on Sat November 22, 2008 12:40 PM User is offlineView users profile

mk378,

So you are saying remove the pressure switch connector, short it, let it run at whatever low pressure it goes to, and see if the temperature switch cuts off the compressor as the register temperature gets very cold?

Check out my cheap low pressure gage pressure tester.....using this my AC low pressure gage checks out exactly with two of my tire gages that have been calibrated at the tire store, in the 10-30 psi range. It's not my gages, these pressures are real. I think maybe Monday we should take the pressure switch we bought back to the dealer and have their mechanic confirm that it's switching too low. I have never seen the charge level effect the low cycle point, if the charge is low the system usually has trouble pulling down to the low pressure condition. The system is putting out tons of cold air.




Edited: Sat November 22, 2008 at 1:44 PM by rm32644

mk378 on Sat November 22, 2008 1:06 PM User is offline

I think you could try that. Don't do it for very long though because you might have poor oil return, especially if undercharged. Measure the air temperature first with everything plugged in and if it goes below 36 or so there is a problem.

I couldn't find any specific tests for the temperature sensor but there must be a resistance specified somewhere. Look in the air duct just after the evaporator for a little 2-wire device.

bohica2xo on Sun November 23, 2008 12:26 PM User is offline

Good grief. All that work to calibrate a gauge from a two dollar tire gauge. A giant step backwards.

If you really want to calibrate your gauge set, simply ice down a can of refrigerant - and look at the P/T chart for that refrigerant.

There is absolutely NOTHING wrong with your LPCO switch. It is NOT the evaporator temperature control in that system. If your system is cycling on that switch it is either undercharged, or the evaporator air discharge sensor is bad.

The sensor on the 2003 Taurus is behind the glovebox. It is snapped into the plenum, and has a two wire connector. Buy one at the dealer, and you will know exactly what you are looking for.

B.

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"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.

rm32644 on Sun November 23, 2008 9:51 PM User is offlineView users profile

bohica2xo,

Thanks for your comments, it sounds easier than I thought to get at the evaporator discharge switch.

"If you really want to calibrate your gauge set, simply ice down a can of refrigerant - and look at the P/T chart for that refrigerant." I have to say "Good grief" to your method. That would cost me $6 for a can, because I would have to puncture it to measure the pressure. Plus it would take longer to get it to a certifiable temperature. I assume you are talking about ice in water at 32F, ie: 28 psi for R134a, one pressure check. I like my method better, I can check all pressures from 50 psi down with stuff I have on hand.

bohica2xo on Tue November 25, 2008 12:21 PM User is offline

GIGO.

I have never seen a stick type tire pressure gauge that was accurate, linear, or would repeat very well.

I would much rather have a gauge that was properly calibrated in the critical range it will be used in, than 50 points on a curve that was developed with a 2 dollar tire gauge.

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.

rm32644 on Tue November 25, 2008 7:11 PM User is offlineView users profile

If you want accuracy, for $6.99 you can get a pencil tire gauge accurate to .5 psi in the range of 5-99 psig, at: http://www.amazon.com/gp/product/B000O9IS2Y. Still in the price range of a can of R134A.
Specification at https://earthaidkit.com/buy/accutirepencilgauge.php

bohica2xo on Wed November 26, 2008 2:26 AM User is offline

Thanks, but I will stay with my 0 to 100 psi 10 inch face Heise gauge for that job. Yes, I send it out for calibration on a regular basis.

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.

mk378 on Wed November 26, 2008 10:09 AM User is offline

Checking your manifold gauge at zero once in a while should be sufficient. While not connected to a car, loosen the hose at the manifold and let the pressure out. If the gauge is way off of zero, assume that it is tweaked and replace it. If it's a little off, use the screw on the dial to rezero it.

Also when you first connect to a car that has had the compressor off for a while, high and low side should almost always read the same. This checks that you have a proper connection and also confirms the two gauges against each other.

rm32644 on Wed November 26, 2008 7:53 PM User is offlineView users profile

bohica2xo

I envision you as a PhD with a lab who likes to do things right. I appreciate you comments and drive for accuracy.

mk378

Thanks for the practical tips, yeah those checks should tell you if something is starting to drift.

Well next week per bohica's recommendation I am going to seek out the evaporator temperature switch, and see if I can impact the low pressure end of the system cycling on my friend's Taurus. The poor guy spent $500 at a Ford dealer for this specific problem and they didn't fix it. I saw the receipt. They played with the plenum doors and blower, no mention of a freezing evaporator shutting of the air flow after an hour, and the clue of a huge puddle under the car an hour after vehicle shutdown. Summer and winter (defroster on in winter). I'm just trying to help him find root cause on a budget. And I'm not trashing Ford, usually they do a great job on problems like these, but in this case I don't think they fully understood the failure description and symptoms. Thanks for all help so far.

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