A/C fast cycling: different situation I guess

[mfernandes]

Well, this is odd and hopefully someone out here can help me.

As title says, my A/C compressor is cycling too fast; 3-4 seconds on and then 2-3 seconds off, then over and over again.

Please take a look at this video; THIS IS MY TRUCK RUNNING:
https://youtu.be/weOkUdkwjmQ

Low on R-134a? Maybe, but the air conditioner blows ice cold inside the cab.


Please note the following:

1- Ive disconnected and jumped the low pressure switch: the compressor runs constantly blowing ice cold inside the cab.

2- There are absolutely no leacks on the a/c system. NONE

3- Whenever the a/c clutch engages/disengages, I can hear a "click" comming from the fuse-relay box inside the engine compartment. Im not sure if its the WOT relay (maybe), but when the compressor turns on, I can clearly hear a relay clicking.

4- The a/c clutch engages and dissengages perfectly. No strage sounds, no spinning when dissengaged, nothing.


So, as far as I know, this could be:

a- low R-134a refrigerant

b- bad low pressure switch (Ive ordered a new one from Rockauto just in case).

c- both a and b.


Can somebody help me?
Any input, test I should do, anything!
Thanks a lot for your time!

 

[kimcrwbr1]

I would just add some refrigerant and see if it stops fast cycleing. A manifold guage set will tell you what the pressures are doing but bypassing the low pressure switch eliminates the WOT relay and computer. It could be either or both low charge or LPCO or a dirty expansion device. My concern would be if there is a restriction in the orifice you wont be getting enough oil back to the compressor. You need to look at both the high and low side to determine that. You dont want to replace the compressor any time soon.

 

[mfernandes]

Thank you very much for your answer man, I really appreciate it.

The orifice tube is brand new, in fact, my truck came from factory with no a/c, i installed the system last year. Heres how I did it: http://www.therangerstation.com/forums/showthread.php?t=160760

I took the time and patience to buy every single oem component, nut, washer, hose etc etc. All the parts are oem and new, and I followed the shop manual when installed the a/c.

The only thing Im suspecting now, is the WOT relay (which was already installed on the truck from factory, prior my a/c installation) which clicks on and off when the truck is on idle.

Correct me if Im wrong: even if the system is low on R-134a, the wot relay shouldnt click... right?

 

[kimcrwbr1]

You said you bypassed the low pressure switch and it cured the cycling problem is that correct? That tells me it is pressure related. How did you evacuate the system exactly before adding the charge? All it takes is a single drop of water to contaminate the system and plug the orifice. Do a soap test by spraying soapy water on all of the fittings looking for bubbles if it is leaking it is a real slow leak. You want to pull it into a deep vacuum for at least 2hrs and then add the refrigerant by weight for the proper charge. Overnight is even better you can never evacuate the system too long especially if you suspect water in the oil it will boil out.

 

[mfernandes]

Thats the crazy thing, I took the truck to be charged by a professional, but im sure its undercharged.

This tuesday Ill take the truck again, Ill check the pressure with the manifolds gauges at the garage and if its low, Ill ask him to evacuate everything and refill with new gas and oil.

Yes, when I bypassed the low pressure switch, the a/c compressog engaged perfectly normal and blower ice cold air. This tells me is pressure related; either low on freon, bad low pressure switch or both.

What do you think?

 

[kimcrwbr1]

If it is low pressure on the suction side but high pressure on the liquid side you have a restriction. If you just add a little juice and it runs normally you probably have a small leak. There is a small chance the pressure switch is faulty. Until you put the guages on your just guessing and that can get expensive.

 

[mfernandes]

I havent recharged the system since it was charged last october/november 2014.
In exactly 1/2 hour im leaving home and buying a set of manifolds.
Ill test the pressures at noon and post the results here.

I bet 3 to 1 its low on refrigerant!

 

[mfernandes]

Ok guys, so I got a nice set of a/c pressure manifold gauges and did a test just a couple of minutes ago.

I have a couple of pics and a video, which Ill upload later today.

These were the readings:

STATIC TEST (engine off)

LOW LINE: 62PSI

HIGH LINE: 60PSI


A/C RUNNING (ON IDLE)

LOW LINE:
min: 24PSI
max: 44PSI

HIGH LINE:
min: 85PSI
max: 150PSI

For your consideration:
1- with the a/c nunning the temp on the center vent register was 4,3°C (arround 40°F)
2- Its very humid today, in fact, its been raning for a couple of days.
3- Outside temp arround 15 to 18°C (59 to 65°F)

ANY IDEAS?????

 

[kimcrwbr1]

Add some refrigerant and see if the pressures come up equally. The static test will tell you two things the most important is if the refrigerant is contaminated. Pressure and temp is allways relevant. With everything outside temp compare the pressure temp on the guage with outside temp the temp on the guage set should be real close to outside temp. Add refrigerant until the system stops fast cycling it probably wont take much then do a soap test on all the fittings you likely just have a small leak. When you evacuated the system how long did you vac it down?

 

[kimcrwbr1]

http://www.pacificseabreeze.com/tech-library/heat-and-insulation/R134a-PT-Chart.htm
According to this you system is not contaminated. Just for reference you do not use static pressure to check the charge 1oz of refrigerant has the same pressure as 1lb. Being under charged your probably gonna freeze up the evaporator coil until you bring up the suction pressure to just above freezing 34 degrees f. Rule of thumb is 2 1/2 times the outside temp for the liquid pressure depending on engine rpms.

 

[mfernandes]

Thank you so much for your answer again dude.

I took the truck to a professional a/c shop here i my town. I really cant tell you for how long they vacuum the system before adding the oil and refrigerant.

Tomorrow morning Ill take the truck again to the same shop; should I ask them to fill some more refrigerant and see what happens? If after refilling the system the a/c cycling continues the same, should I ask them to vacuum everytghing and star over again???

Here are the pics of the gauges and also the video with the system operating:

Low side static reading:

High side static reading:

Both at the same time:

So, as far as I know, on the static test its ok for both gauges reading the same (around 60PSI), so thats good!

This is the video with the a/c running on max vent and max a/c, full cold offcourse!

https://www.youtube.com/watch?v=MytvSHazO44&feature=youtu.be

Any input will be appreciated!!!

 

[kimcrwbr1]

How much refrigerant did you add? The low pressure switch is working correct it cycles off at around 25psi and on around 45psi and you not going high pressure just add more refrigerant. One of those digital bathroom scales may work. If your adding vapor it can take a while just keep adding refrigerant until the system stops short cycling. Weigh the can of refrigerant before and after to see how much it took. The shop will charge you to tell you it has a leak. sometimes you can just tighten a loose fitting yourself and save yourself some money. Just remember every time you hook up a set of guages you remove close to 1 oz of refrigerant so be prepared to add a little. be sure and soap spit test the service disconnects as you could possibly have a leaky schrader valve after you disconnect the guages.

 

[mfernandes]

Thanks man.
The system was refilled last year by an a/c technic here in my town.
In my opinion, its a little low on refrigerant as you say.
Today is tuesday, Ill have the system checked in a couple of mins.
As soon as I get back Ill post the results.

My big question is: I HEAR THE WOT RELAY CYCLING (yes, Ive tryed to swap it).

If its low on refrigerant, can that trigger the low pressure switch and the wot relay???

I jumped the low pressure switch and the compressor engaged and blowed ice cold.

 

[kimcrwbr1]

My guess is the computer controls the low pressure cutout using the WOT relay. Maybe they should just call it the compressor relay as it sounds like it serves dual purpose. The low pressure switch is just a input to the computer? IDK for sure the WOT cutout is normally controlled by input from the throttle position senser (computer controlled).