A/C compressor is short-cycling

[92ShoOff]

Okay so I'm not sure if my refrigerant pressure is too low or too high. Either way, the compressor is cycling on and off every few seconds constantly. So right now with the engine warmed up and the A/C on the pressure was reading 45 lbs., so assuming the system was low I hooked up a can of R134A to my guage and let it open. The gauge immediately rose up to around 100 lbs. and after 20 minutes the guage did not change. I wanted another 10 mins and still the same reading of 100 lbs and the compressor was still short-cycling. I felt the weight of the can and it seemed as if nothing had left the can. Felt just as heavy as it was before I pierced it.

I unplugged everything and thought maybe the pressure was too high and wasn't letting the refirgerant out of the can go into the system. The can says that the system is charged anywhere between 25 lbs. and 45 lbs., so I let refrigerant out of the low pressure line until I got 25 lbs. The compressor was STILL short-cycling. Also, the radiator fan is coming on everytime I turn the A/C on. Whether I just started up a cold engine and kicked the A/C, or even if I'm cruising down the highway in 45 degree weather... the fan is on. Is the fan supposed to be on 100% of the time that the A/C is on? I had to replace the fan motor when I first got the car because it was already done for... and I would think that with this motor kicking in the whole summer, this brand new one from Motorcraft is not going to last very long.

So does anyone have any idea why my system is short-cycling? I will adding more refrigerant tomorrow after the engine has cooled down over-night. This time I'll try adding refrigerant while the engine is off also, and bring it up to 95-100 lbs. like someone else suggested one time before. Any help will always be appreciated as always.

Thanks!

-Andrew Grayson

 

[Rob94]

Yes, any time the climate control is set to a position that requires use of the AC compressor, the fan will run. As far as your "short cycling", I'd suggest changed the clutch cycling switch located on top of the dryer. $30 from Ford.

 

[projectSHO89]

You are incorrectly using the guage that is hooked to the can of refrigerant. The reading that you are seeing while the valve on the can is open is the pressure from the can , not the operating pressure in the system. You have to close the valve at the can to read the actual system pressure.

Since it sounds like you only have the single guage instead of a proper manifold set, follow these directions.

Measure the static pressure of the system before starting the engine . Make sure the engine is stone cold. Depending on the ambient temp, you will see a reading (in a properly charged system) of between 60 to 110 psi, more or less.

Start the engine and engage the A/C system. When the compressor engages, the pressure reading should drop until it reaches 20-25 psi. At this time, the compressor clutch should disengage and the measured pressure should rise. Once it hits around 45 psi, the pressure cycling switch should close and the process repeats.

Short cycling usually occurs when there is an insufficient volume of refrigerant in the system. If this is the case, the guage indication (when properly used) will make this obvious.

In the event that a switch is needed, they are $12.99 at Advance Auto.

And yes, as pointed out, the fan runs any time the A/C system is supposed to be engaged.

Steve

 

[Coil99]

Either way, the compressor is cycling on and off every few seconds constantly.

I'm having the same problem. Thanks to Rob94 and projectSHO89 for some great advice. I hope it is simply "an insufficient volume of refrigerant in the system" as projectSHO89 noted and not something more serious.

 

[92ShoOff]

Yeah see I obviously don't know what the heck I'm doing with this A/C stuff. My dad just got all ****** and told me to do it myself. Kinda difficult when you know zilch about what you're doing lol.

Anyhow, I was using a single gauge... but I do have a set of manifold gauges as well... just don't know how to use those either. My dad does though. All sounds well about the info you just gave me, but I guess I can't do anything until i get this short-cycling taken care of. I guess I'll be replacing that switch now too, on top of the other 5 various sensors that I've had to replace over the past weeks due to my check engine codes I was getting on them. Damn these cars really ARE a hobby lol.

And another thing was today with the A/C on I heard a slight chirp coming from underneath the hood when the RPMs reached around 4k or so when I was accelerating heavily. I think as you suggested last time Steve, my clutch may be bad. Is that something simple to replace, and about how much might I expect to pay for once if I need to replace it?

But yes, as Coil99 said, you guys have been really helpful... and Steve has helped me out several times already and given me advice that undoubtedly solved my problems. Thanks for your time.. it means a lot to me since I'm still learning about these cars.

 

[Coil99]

I hope it is simply "an insufficient volume of refrigerant in the system"

Well, the good news is that it was low on refrigerant. Adding about 2 cans has it working again.


But, the bad news is that the compressor appears to have a very small leak around the front...bad seals, maybe? I hope the leak stays very small <knock on wood> and can hold out for a good while.


I was told I was looking at $850 to $950 in parts and labor to replace the condensor and tend to all related matters. Does that sound about right?

 

[Rob94]

If you system is still the old R12 refrigerant, then yes, that is probably an accurate price. The shop would have to evacuate the system (can't vent R12 to the atmosphere). R12 is also EXTREMELY expensive. The average Joe can not walk into a store and buy it anymore. Each year, the price goes higher and higher. I'm not sure what it is going for yet this year. If you have a leak at the compressor, why would they need to replace the condensor anyways? It's just two o-rings at the compressor.

 

[rangerj]

The leak behind the A/C clutch assembly is the compressor shaft seal. The shaft seal for the SHO compressor (Nippondenso 10-P-15F) is about $70, and the special tools to remove and replace the seal are about $125. For a few dollars more you can buy a rebuilt compressor!

The special tools are 10-P-15-F compressor "specific", that is you will have an expensive tool set that is limited to one specific compressor model. (I have the tools, but I'm **** about fixing things rather than replacing them. However, this was a dumb move on my part. If I had it to do over I would have gotten a rebuilt compressor. )

If your compressor is working well otherwise, you can add a can of refrigerant that has a sealer in it and see how long the charge lasts. If your system has R-134a in it this would be very inexpensive.

As for doing the job yourself, and not knowing what you are doing, is VERY dangerous. Refrigerant is liquified at temperatures below -250 degrees F.
If you get ANY in your eyes you may be injured for life. If you hook up to the high pressure line by mistake, the pressure could cause the can to explode like a bomb.

If you do not know what you are doing, DON'T DO IT. rangerj

Rob, the last I heard R-12 was at $85 to $90 per pound. It will continue to go up as it becomes rarer. It can no longer be made or imported into the U.S.

 

[Rob94]

Rob, the last I heard R-12 was at $85 to $90 per pound. It will continue to go up as it becomes rarer. It can no longer be made or imported into the U.S.

Last summer, the cheapest I was able to find it for was $125/lb. I've heard rumors of it being close to $200/lb this year. At that price, it would be cheaper to just do the R134a conversion.

And Ranger is absolutely correct. Aside from the pain-in-the *** factor, AC work can be IDLH (Immediately Dangerous to Life or Health) if you do not know what you are doing. One small blast of refrigerant on bare skin can frostbite instantly. Disconnecting a line without properly evacuated the system can cause you a world of hurt that you'll have to live with forever. It may be expensive, but this kind of work is best left to those who have been properly trained.

 

[rangerj]

Rob,

As you know the smallest quantity of R-12 you can buy is 30lbs. At $125 a pound that is a big investment. A good friend of mine, a fellow Ford fanatic, is in the business (auto A/C) and he evacuated a system that the customer swore had never been worked on.

Well, the customers system had some of that crap from Mexico in it and it ruined a half bottle of R-12. Guess who does not want to pay for it? The evacuation equipment also has to be sent back to the manufacturer to be cleaned out, etc. By the time this is over it will cost my buddy about $5,000.

He stopped doing anything with R-12. He won't touch it. You know darn well a customer will not pay the $25,000 fine, but they all want you to do something illeagle "on the cheap". If they won't pay for a full conversion, including a new filter dryer, high pressure line, and a complete system clean-out, then they can go somewhere else.

Isn't dealing with the public fun? rangerj

 

[uSHOslow]

On a side note, if your a/c compressor is cycling on and off you should discontinue use of it. As the head a/c engineer at Visteon told me, the refridgerant pressure also pushes the oil for the compressor through the system. If there is no refridgerant pressure then there is little or no lubrication. Which could end up leading to your compressor siezeing.