Automotive Air Conditioning Information Forum (Archives)

mekelly on Thu June 02, 2011 7:31 PM

Year: 1999
Make: Ford
Model: Expedition
Engine Size: 5.4
Refrigerant Type: R-134a
Ambient Temp: 95
Pressure Low: 55
Country of Origin: United States

I own a 1999 Ford Expedition with the 5.4L engine. My son drives the car and started complaining the A/C wasn't working.

I put a gauge on the low pressure port and it read 55 with an ambient of 93 degrees so I think refrigerant level is OK.

I then turned on the car, ran both (front and rear) A/C's at max and the low side pressure would cycle between 20 and 45 every 3 seconds. In other words, three seconds to go from 20 to 45, it would then take three seconds to drop to 20 again. This continued for the several minutes I ran the engine. There was also sort of a 'winding up and down' sound as it cycled. It seemed to me that a solenoid or clutch or something was cycling/engaging every three seconds (but I could be totally wrong).

While I didn't actually measure the temperature of the air coming out of the vents, it was clearly very warm. Can't say the A/C didn't have any effect at all, but if it did, it was minimal.

Any thoughts, suggestions, recommendations as to what's wrong or where to go from here?

Thanks in advance!

Mike

Cussboy on Thu June 02, 2011 8:11 PM

Quote
Originally posted by: mekelly
I put a gauge on the low pressure port and it read 55 with an ambient of 93 degrees so I think refrigerant level is OK.

Says who ??? One cannot assess the refrigerant level by reading static pressure. That's hard enough reading both low and high pressures at 1500-2000 rpm.

I suspect your refrigerant is low, and when the compressor engages the low pressure drops lower than the pressure switch limit, so it turns it off. How low? The only real way is to pull out the refrigerant and weigh it, then put the correct amount in.

But if you are low now, you have a leak. This could be from small leakage over the last decade through the compressor seal (which would not be a big problem, just replenish the refrigerant) or a newer, larger leak which needs to be fixed.

mekelly on Thu June 02, 2011 8:26 PM

Thanks for the quick reply!

I understand the best way to determine how much refrigerant is in the system is to evacuate it and weigh it but is there NO value in looking at the low side port pressure? Since it was reading 55 with an ambient temp of 95 I thought I could conclude that it was good (or at least very close).

That coupled with with the fact that the air was blowing very warm led me to believe something else was going on. However, I like YOUR conclusion better and hope it is just low refrigerant levels. Given that I am getting a low side reading of 55 I am certainly not going to add any refrigerant on my own if I can't tell when I am overfilling it.

So it sounds like I should take it to an A/C shop for further diagnosis.

Anything else I can/should do on my own to troubleshoot/fix?

Thanks again!

mk378 on Thu June 02, 2011 11:13 PM

55 with the compressor off is no good, unless your ambient is 50 F. At 90 F it should be more than 100 psi. This shows there is practically no refrigerant left. That is consistent with the short cycling of the compressor. It has nothing to pump so the pressure drops to 20 rapidly and it cycles off.

You could probably restore operation merely by adding a bunch of refrigerant (nearly a full charge) but it's just going to leak out again. If it worked OK a few weeks ago and now you have this, a serious leak has recently developed.

Edited: Thu June 02, 2011 at 11:17 PM by mk378

JJM on Thu June 02, 2011 11:33 PM

A proper gauge set would also confirm a positive diagnosis, but we're going nowhere with these silly chain store charging kits.

I don't know what's going on... did they stop making manifold gauge sets?

Joe

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

mekelly on Fri June 03, 2011 8:33 AM

Thanks for all of the replies. I am pretty sure the leak didn't suddenly happen, I believe it's been a slow leak for several years (my son drives the car so I am not exactly sure). But everything that's being said makes sense. I will add several cans of refrigerant as I believe it's probably a very slow leak as see what happens.

Cussboy on Fri June 03, 2011 9:12 AM

Quote
Originally posted by: mekelly
Thanks for all of the replies. I am pretty sure the leak didn't suddenly happen, I believe it's been a slow leak for several years (my son drives the car so I am not exactly sure). But everything that's being said makes sense. I will add several cans of refrigerant as I believe it's probably a very slow leak as see what happens.

Use a gauge set and your target will be about 250 psi on the high side at about 1500-200 rpm. We don't recommend just blindly adding refrigerant.

mekelly on Sat June 04, 2011 9:24 AM

OK, I am not sure if I have a major leak or just need to add a lot more refrigerant but wanted the opinion of the experts.

Attempted to add refrigerant to the Expedition. Ambient temperature was 75. While adding refrigerant the compressor would still cycle every 3 seconds between 35 and 45 on the low pressure port (as opposed to 25 to 45 a day ago, without adding refrigerant, just monitoring pressure while compressor was cycling). Put in about 8oz. Stopped adding refrigerant and pressures went back to cycling between 25 and 45.

So not sure which scenario is most likely:

1. Low pressure port always reads higher when you're actually adding refrigerant and drops when you close the can tap. Meaning I just haven't added enough refrigerant and I am still way low, need to add more.

2. I have a major leak and the refrigerant is leaking out as soon as I can get it in the system.

3. I am just still way low on refrigerant, adding 8oz. didn't change much and I should add additional refrigerant until the compressor stops cycling every 3 seconds (checking at least the low port pressure of course).

I don't want to keep adding refrigerant needlessly if there's a major leak but my suspicion is the system is so low that I need to add additional refrigerant to restore normal operation (per mk378 above). I am trying to secure a real gauge set to monitor high and low pressure but in the meantime, is it OK (I know not ideal) to add additional refrigerant to try to get the compressor to at least stay on while ensuring the low pressure port doesn't exceed its expected pressure at ambient temp?

Don't understand why the pressure drops 10-15 pounds when I close the tap on the can while the compressor is running.

Thanks for all the help!


Edited: Sat June 04, 2011 at 9:34 AM by mekelly

tomw on Sat June 04, 2011 1:04 PM

The pressure drops when you stop adding refrigerant by closing the tap because the compressor is sucking it all out of the evaporator, accumulator and return line. It's on its way to the compressor to get compressed and then on to the condenser. Your system sounds to be still low on refrigerant. If the refrigerant is staying in the system, you should start to see a little improvement in cooling air coming out of the registers as you add.
Check the label on the underside of the hood or on the radiator support. It will tell you the amount of refrigerant the system was designed to hold.
For what it's worth, the refrigerant is a gas at ambient temperatures such as 95, actually a lot lower. It will expand to fill the whole system as long as there is enough gas{and NOT air} and will maintain the pressure at a specific temp. R134a will have x.x PSI at xx F. As long as it can expand to fill the system with pure gas.
Your system is very low, as it was only 55 psi at 90+. There was not even enough gas to fill the system at its standard pressure / temperature. There is a chart for each refrigerant that denotes the pressure temperature relationship. R12 would 'boil' at about 32F at close to 32 psi. So it was a natural for cooling systems. Just keep the pressure a bit below 32 psi in the evaporator{by the compressor sucking the gas out... as yours is doing} and the evaporator metal would be darn close to 32F. I think the R12 LPCO switches were set to open at around 27-28F. If this doesn't make sense, please comment.
tom

-------------------------
simplificate and add lightness

mekelly on Sat June 04, 2011 1:47 PM

Tom, thanks for the great reply. I think I follow what you're saying and your analysis sounds right on. My system does use r-134a not R12. Not sure if you were implying that or just explaining the behavior of R12 systems.

I have two 12oz cans of r-134a left. My plan would be to add them until the compressor stops short cycling. I am also monitoring the low side pressure but I assume that should not rise above whatever the correct psi is for the ambient temperature is if the compressor is still short cycling (or reading below the correct psi when I close the tap). Anything else I should be watching (other than seeing if the vent temps improve)?

mk378 on Sat June 04, 2011 2:09 PM

Please don't continue without a proper gauge manifold. When trying to "top up" it is essential to watch the high side pressure. That pressure will tell you a lot more about the state of charge (or overcharge) than the low side does. You can shop local parts stores for one. I don't think they've stopped making them. Often they are behind the counter (along with the 30 lb cylinders of R-134a) and you have to ask but they'll gladly sell you one.

Like Tomw said, find the manufacturer's specified weight either on the sticker or service manual. Be sure to not use more than that. A SUV with dual air typically needs quite a bit though. It seems expensive to just charge that truck and have it leak out again.

Edited: Sat June 04, 2011 at 2:11 PM by mk378

mekelly on Sat June 04, 2011 2:26 PM

Thanks. I did stop at my local auto store this morning and they said they typically carry them (NAPA) but didn't have any in stock.

I did just add some refrigerant that got the compressor to stop short cycling and it's definitely blowing much cooler air. Since I can only look at the low side now I have charged it to 45psi at an ambient of 90. My chart say 45-55 at that ambient. At that point I couldn't tell that it was taking new refrigerant, but was going to stop at 45psi anyway without a high side gauge. I assume it's typical for the outflow from the can to slow as you near operating pressures or will it continue to take refrigerant well over operating specs?

I will check pressure again tomorrow and at least see if it's lost any pressure.

Thanks again for all the help, tips, guidance, and safety cautions!

Edited: Sat June 04, 2011 at 2:27 PM by mekelly

HVACNY on Sat June 04, 2011 3:05 PM

Why aren't you adding dye to find the leak??That was the original issue..

mekelly on Sat June 04, 2011 6:28 PM

I had several cans of refrigerant at home that didn't have dye so I wanted to add those first and see if I could at least get the air cool and running normally. Now that it's at least working semi well, I'll try to see if I can find the leak.