Normal A/C cycle?

mfernandes · #1 08-13-2015, 12:23 PM

Hi pals.
Hope somebody here can help me, only thing you should do is take a look at this video and compare it with your truck:

My A/C blows ice cold air, it works perfectly, but I think its cycling too fast.

Can anybody tell me if its working correctly or, if indeed, its too fast?

Thanks a lot in advance guys!!!!

cvar · #2 08-13-2015, 01:02 PM

Cycling is way too fast. Your ON & OFF times are very short (3 seconds ON, 3 seconds OFF). That's what happens when refrigerant charge is low.
Should be about 10 seconds ON, 9 seconds OFF (depends on outside ambient temperature). See the graphs in here (near bottom) for expected cycle times:
http://imgur.com/a/xMUKH

mfernandes · #3 08-13-2015, 01:17 PM

Thats what I thought... too fast.

So, my a/c charge is low?

At the moment of making the video, the settings where normal a/c (not max a/c), full cold and ventilation on 1st. speed (lowest).

mfernandes · #4 08-13-2015, 07:06 PM

Ill ask for a favour; can somebody please make a video and uplode it to double check how is the correct cycling (on and off) of the compressor clutch?

Its winter here (arround 15°C/60°F) so the cycle should be on-off arround 10 secs... right?

Hope somebody can make a video, Id really appreciate that!!!!

Thanks a lot in advance

mfernandes · #5 08-15-2015, 08:23 AM

UPDATE!!!

Went to the garage, and I suspect my problem is part low on R134a and part a bad low pressure switch.

What I did was:
disconnected the low pressure switch and jump both terminals with a paper clip, turn on the engine and set to max a/c, full fan speed and offcourse, full cold.

With the switch jumped, the compressor kicked on permanently (never shut off) and the a/c blowed ice cold.

Now, according to the Ford service manual:
1- If compressor engages and systems cools, the switch is most likely bad. And,

2- If the compressor engages but the system does not cool, you should suspect that you have no refrigerant.

In my opinion, like I sayed, my problem is part low on R134a and part, a bad low pressure switch, as when I bypassed the switch the compressor would have kicked on (like it did) but should not have blown cold air inside the cab.

What do you think? Any input will be appreciated!!!
Thanks a lot!

mfernandes · #6 08-15-2015, 01:09 PM

UPDATE 2!!!

Im geting closer and closer, I think

When the A/C compressor kicks on and off, I can clearly hear the WOT relay clicking.

Question is; im sure this truck is a little low on R-134a, so, the low refrigerant would trigger the low pressure switch, but, can the low pressure switch trigger the WOT relay?

Like this:

low pressure switch ----> ECU ----> WOT Relay???

What do youn think???

cowboybilly9mile · #7 08-15-2015, 03:30 PM

Until a gauge set is hooked up to the AC system and the blower and engine speed are appropriate for taking meaningful gauge readings (and ideally the outside temperature is warm), you will not really know what is going on. Low ambient temps + low blower speed = short cycling A/C on any vehicle that uses a low pressure cutoff switch and an orifice tube; this as opposed to the expansion valve setup used back in the good ol' days. While short cycling can be an indicator of low charge under the just noted operating condition, it all goes back to the first line in this post. Short cycling can be indicative of a problem, but by no means is it in itself an absolute and proper diagnoses of anything.

mfernandes · #8 08-15-2015, 03:53 PM

Ok, first of thanks a lot for your answer.

Second, Ill have the system checked this week.

As I dont have the correct chart, Ill be using this Chryslet chart as a guide, Im sure operating system pressures will be close.

So, according to this guide; I should have 112 to 210 PSI on the high pressure switch and 10 to 37 PSI on the low switch... right?

Im 99% positive the system is low on gas, which makes the low pressure switch open, which tells the ecu and the WOT relay to cut the current to the compressor.

Could this be correct or am I saying something stupid???!!!

cvar · #9 08-15-2015, 06:17 PM

The proper chart is here:

So at 15C ambient temperature, your HIGH pressure side should be between 110 to 200 psi,
your LOW pressure should be between 20 to 50 psi, and coming out of your vents the cooled air should be between 2 to 7C.
The clutch ON time should be between 5 to 10 sec. The clutch OFF time should be between 8 to 11 sec.

mfernandes · #10 08-15-2015, 06:35 PM

Couldnt be more clear. Thanks a lot sir!

This tuesday Ill take the truck again to the shop which charged the system last year. Im sure, 99% sure its low on R-134a and/or a bad a/c low pressure switch.

Maybe the problem is that the owner of the shop is a german old guy who barely speaks spanish, communication breakdown? Maybe!

As soon as Ive got answers Ill let you know.

97rangerstepside · #11 08-15-2015, 10:42 PM

I'm gonna follow this, been having a very similar problem for quite awhile now. Looking forward to seeing the conclusion

mfernandes · #12 08-16-2015, 06:03 AM

Wait till tusday, as soon as I got this figured out Ill put the results here.

Totally sure this is low on freon and a bad low pressure switch.

When I installed the a/c last year, I bought everything from USA and some small parts from Mexico (Compressor, condenser, evaporator, wiring harness, orifice tube, manifold from USA; condenser support, rubber moldings and screws, nuts and bolts from Mexico), but the only part I bought from a Ford Dealership here in Uruguay was the low pressure switch.
The box was brown and with signs of humidity, this is, it was in stock for several years and never was sold.

Im positive this switch could be failing as well!!!

cvar · #13 08-16-2015, 06:44 AM

What are your high & low side pressures? Have you measured? You may consider getting a set of used manifold gauges? The orifice tube might be plugged if your new A/C system had particles that became dislodged in the past year. It doesn't take much to plug that O-T.

mfernandes · #14 08-16-2015, 07:31 AM

All the components are brand new. Last year when I installed the a/c (heres how i did it: Complete A/C installation... from scratch!) i put an oem brand new blue orifice tube.

I didnt meassure the pressures yet, as soon as I get to the a/c shop this tuesday the first thing Ill ask for is to messure the system pressure. If the system pressure is correct, Ill replace the o.t. and low pressure switch.

Do you think the o.t. may have got dislodged even when all the parts were brand new? What would have made the o.t. to get dislodged?

cvar · #15 08-16-2015, 08:51 PM

No, I don't mean that your o.t. was dislodged. I mean that a particle of dirt (or maybe a flake of telflon from inside the compressor) might have been dislodged and set free from wherever it was lurking, and now that piece of loose dirt has travelled to your o.t. and clogged the tiny orifice.