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jeep wranger pressure readings

gfinc on Thu April 12, 2012 7:45 PM User is offlineView users profile

Year: 2000
Make: Jeep
Model: Wrangler
Engine Size: 4.0
Refrigerant Type: 134
Ambient Temp: 80
Pressure Low: 10-40
Pressure High: 75-100
Country of Origin: United States

2000 wrangler 4.0 liter

I bought this 6 months ago with 55k miles. GREAT JEEP but now summer is here in Florida.

AC is not cold. With AC turned on, air from vents goes from hot to roughly ambient temp when I switch the thermostat on the dash from hot to cold, so I suspect the mix door is working.

Compressor cycles every 5 to 10 seconds. Refrigerant line coming out of the firewall gets cool (not real cold, though).

I didn’t want to screw anything up by just buying a recharge kit and plugging in a can of 134, so bought a set of manifold gauges to test things out first.

I hooked the blue side to the refrigerant line port near the firewall and the red side to the port on the refrigerant line at the top/front of the engine. Opening one valve with the engine off jumped the blue side up to around 70 and the low side at around 150-ish – which doesn’t jive with any of the static readings the forums suggest I should expect.

I turned on the engine with AC on, and the reading on both sides jumped as the compressor cycled, but blue side was still high.

I shut it down and let it sit. I reconnected after 20 minutes with engine off, and opening either value resulted in static pressure of around 50 on both sides (go figure). Turning on the compressor has the low side cycling from 10 to 40 and the high side from 75 to 100.

I don’t know why I had the initial weird readings. I thought maybe the hoses were connected backwards or something, but I don’t think so. Now I presume I am low on refrigerant?

Any help appreciated. I wanna do this right if I can

Cussboy on Thu April 12, 2012 8:16 PM User is offline

Quote
Originally posted by: gfinc
2000 wrangler 4.0 liter

I didn’t want to screw anything up by just buying a recharge kit and plugging in a can of 134, so bought a set of manifold gauges to test things out first.

That was EXTREMELY smart. Yes, your pressure readings indicate low refrigerant charge. And that means that you do have a leak. Although it is possible that typical attrition (leakage) from the compressor seal over 12 years could result in that.

So your choice whether you should have it checked for leaks (soap bubble check, UV dye addition, electronic sniffer) and repaired if leak found, or just add R134a (such as one full can, and post pressures then) and wait and see if cooling is adequate. Typical summer high side pressures at about 2000 rpm (where pressures should be measured) are about 250 psi.

mk378 on Thu April 12, 2012 11:30 PM User is offline

Make some effort to find the leak. It is nearly empty, you will need near the full rated charge amount to get it working again.

Pressure measurements are always taken with the valve wheels on the manifold closed. They connect the high and low hoses to the center yellow hose when open.

For basic charging, leave the high side wheel closed. Connect a can of R-134a to the yellow hose. You will need a can tapper-- the thread on the hose matches that on the top of the can but it will not work to put it on directly. Loosen the yellow hose at the manifold and tap the can(*), tighten the hose as soon as refrigerant starts to flow and hiss out. That clears the air out of the yellow hose. Now start the A/C and open the low side valve wheel. When the can is empty, close the valve wheel and repeat with another can if necessary.

(*) Turn the handle on the tapper ccw so the needle is all the way up. Attach tapper to can and hose. Turn the handle fully cw to lower the needle, punching a hole in the top of the can. When you turn the handle ccw again the refrigerant will start to flow.

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