AC- 95psi on Low Pressure Side, now what?

[rocketboy52]

I'm newbie to the AC world, but have spent the last two hours going through this AC forum. I have a better idea about the AC system from reading a bunch of Glacier's Posts (THANKS A BUNCH). Here's the deal:

95 OHV 4.0 Explorer w/ 130,000 miles. Recently moved out to Mojave/Tehachapi CA area. AC was working fine until two months ago. On a hot day, I turned on the AC and got only outside air temp (maybe even slightly hotter). I went to Autozone and bought a Quest R-134a refill can and cheapo quest gauge. Read the intructions on the can, turned the Car and the AC on and hooked up the can and gauge to the Low pressure service port. Instantly the Gauge pegged past 100psi in the red/danger zone of the gauge. Not sure I did everything right, I pulled off the can, and reread the instructions on the can. With the engine off, and refill can valve closed, I hooked the gauge to the low pressure side port again and read 95 psi. I'm not sure what this means so I searched for a post here to see if I could find out some more info. I don't believe my compressor is engaging, but I'm not sure.

With AC off, and in Park I idle just under 1000rpm. I turn on the AC and RPM rises to 1100 for a split second and then returns to 975. I don't here a click from the compressor. The only noise I can hear is my Air blower under the dash. I seem to remember when the compressor turned on in the past I heared a distinct click followed by a consistantly higher RPM. I'm not sure what my next move should be. How to tell if the compressor is shot, or the compressor clutch is shot?

I already have a nice vacuum pump (Robinar unit), and I am looking to buy a decent set of gauges next. After that, what should be the first thing I check? Should I check anything else before I reclaim the R134? What can cause the low pressure side to have such a high PSI? shouldnt it be in the 30-45psi range? Thanks in advance for all help

 

[shamaal]

I don't believe my compressor is engaging, but I'm not sure.

When the compressor engages the entire pulley (clutch and nut inside) will turn. If it's just the outside (the nut doesn't turn) then the clutch is not engaging.

Compressor switch kicks in at >47 psi. It should be on. Assuming gauge is correct (big if) the compressor should be running. Jump the switch on the accumulator at the plug. If the compressor kicks in, the switch is bad. It screws on to a schrader valve. Wear eye protection, occasionally the schader valve stcks.

If it does not kick in, with the engine off, turn compressor by hand with a 10mm wrench. If it doesn't turn, compressor has seized. If it turns - clutch is bad. Generally speaking the clutch and compressor are replaced as a complete unit although the clutch can be replaced with a special tool.

The last possibility is the compressor is running and the system is clogged (orifice - most likely)

I'm betting bad switch. Confirm that the compressor clutch is engaged/disengaged and post any questions if you have them.

 

[Glacier991]

Glad you found the threads helpful. Let's back up a bit though..

The pressure of refrigerant in a closed system will vary depending on the outside temperature (ambient). In a system that is off, the low side and the high side are the same! That pressure will be equal roughly (in the case of R134) to the outside temps in the engine compartment. Also it matters not how much refrigerant is in the system, you cannot tell charge on a non-operating system by pressures!!! I REPEAT...YOU CANNOT TELL THE STATE OF CHARGE IN A NON-OPERATING SYSTEM BY PRESSURES!!! It does not work like air pressure in a tire.

As Shamaal said, there is a switch on the accumulator (the black cannister on the passenger side near the firewall) that operates the compressor clutch. It prevents operating without a charge in the system. Why? BECAUSE THE REFRIGERANT CARRIES THE OIL. No refrigerant = no oil = compressor failure.

If there is refrigerant in the system, the system will have a pressure in excess of that needed to make the switch engage the compressor, and the system will operate.

Problems when there is pressure and the compressor will not engage are usually electrical, and can often be nothing more than a bad cutout switch.

With the system on check for the presence of 12V at either side of the cutout... if it is there, try jumpering the connector and see if the compressor runs. Do not run it like this long. Make sure you have over 50 lbs of pressure and if so, then you likely have a bad switch. They can be replaced easily and there is a schrader valve behind it so you do not have to worry about losing refrigerant when you remove it.

In a properly operating system the compressor will cycle, that is not a problem it is normal...

 

[rocketboy52]

Thanks for the tips, I'll check the nut this afternoon to see if I'm the compressor is engageing. After that, I'll check the switch.

 

[rocketboy52]

FYI, the clutch bolt in my Explorer is a 8mm. It turns fairly easy with a socket wrench and feels like it spins smoothly. With the AC "on" I then pulled the switch connector off and jumped the leads on the harness with a paper clip. Still the clutch didn't engage. So from Shaamal's post, it sounds like my AC compressor clutch is dead. Is it worth it to try and replace just the clutch, or it is more prudent to swap the compressor unit? Thanks.

 

[Glacier991]

The tools required to remove and replace the clutch are pricey and not easily available for one time use by amateurs. Most aftermarket rebuilt compressors come with a new clutch... I recommend you replace them as a unit.

 

[CDW6212R]

Autozone carries the AC clutch removal tool, their loaner program. It isn't such a simple job, the "C" clips are interesting to remove, and just a clutch isn't always easy to find. Good luck,

 

[Glacier991]

That's good to know Don. Candidly... settng the air gap etc and removing and replacing JUST the clutch is such a PITA that I strongly.... STRONGLY... recommend replacement of the compressor and clutch as a unit. Besides... they both have useful lifespans, why not start FRESH ?

 

[shamaal]

Directions for the adventurous. I think the Mustang A/C compressor is the same. It's good to know Autozone has the tool; my clutch is beginning to squeel.

http://autorepair.about.com/library/faqs/bl168i.htm

 

[Glacier991]

Nicely done once again Shamaal

 

[CDW6212R]

Well, having the tool on their little counter chart, and actually having it aren't the same. Be sure to call ahead, and inspect it when they bring it out. I've opened the case and found a piece missing before, some people are really hard on tools.