Jeep: 98 Jeep A/C problem

I have a 98 Jeep Wrangler, 4.0 liter inline 6 with A/C that has a
rather interesting problem. When I have the A/C unit on, so long as I
sit at idle and motionless, the A/C pump stays on and thee interior
stays cool. However, once I put it in gear and drive off, no matter
what the speed is (slow or fast) the A/C compressor kicks off and
stays off. The serpentine belt was just changed recently, and the
system was recharged with coolant. The tech who recharged it said that
he took out as much R134 as went back into it. He put dye in the
system to detect leaks, but we've not seen any leaks as far as we
could tell. It's starting to warm up around here again, and I'm
curious what might be causing the problem. Any ideas?

Thanks!

Vince

Hi Vince,
I know what you are talking about as far as the Chiltons being good or
not. I have a 89 YJ, and purchased the chiltons and the Haynes and find
that I have to switch back and forth to find good info, and still it's
flaky at best. I do heating and airconditoning for a living in commercial
but not automotive but the controls are the same, but a little bit
different animals so I'll try and help as best I can. First off, your
friend sounds like he was doing what he could. I would like to know if
there was a previous problem with the system, it sounds like there was
because he was checking it out. Your ac system has a compressor, and a
discharge (supply) line and a Suction (return) line. The return line is
larger than the supply line. The supply line goes to a coil in the heating
ac duct under the dash where air gets blown across it. There should be a
sensor on the large (return) line with 2 wires going to it. This will be
the low pressure cut out. If you jumper across the wires and the system
runs, it could be a bad switch, or you are low on refrigerant. There may
or may not be one on the small (supply) line, which will be a high pressure
cut out and functions the same. They should be normally a closed circuit
unless there is a problem either with the system or the safety switch.
another scenario, I am curious if the system works in defrost.
In defrost mode, the air conditioner turns on, because in cooling the coil
actually collects moisture from the air in the cab. The temp setting on
heat adds hot water to the heater supplying heat to the cabin, and you
don't notice the cooling coil being on.
So, try turning on the defrost, and turning the heat control knob to the
cold section, and you should get the same thing as the ac being on.
You could have a switch problem, or possibly even the belt may be loose.
And when the RPM's go up, it starts slipping. But this is pretty far
fetched. I'd look at your ac coil at the radiator, and make sure its
clean. It is possible your compressor clutch may have a problem as well.
Maybe as the RPM's go up, the clutch disengages.
Look for those two fittings I mentioned, and jumper across the two wires.
Without knowing what your refrigerant pressures are or were after he
charged the system, I can only guess. Those pressures are VERY important
in troubleshooting what is going on.
I would buy the Haynes and Chiltons manuals if I were you. They are
cheaper, and will get you by until you can buy the DC manuals. But I had a
Ford once, and the manuals were almost the same as Fords, so it's a crap
shoot if Jeeps are better or not. Write back and let me know, as I can
give more help with a little more info. Also, do you have a cabin air
filter? If you do and it is clogged, it will block air flow and cause the
low pressure switch to cut out......
hope this helps




1. Previous problem with system?

2. what were the refrigerant pressures if you or he knows? There should be
a high and a low pressure. The machine may have provided it to him, but he
may not have recorded them. He was (I'm assuming) using a reclaim machine
to pull out the refrigerant. When he charged it what were the final
pressures if he remembers...high and low...

3. with the system in your jeep, DC made alot of jeeps, and the refrigerant
charge should be weighed in. So basically, a refrigerant 134a canister
should be placed on a scale, and the system charged to say 2 lbs 6 ounces,
etc...(reference only). Or the system can be charged using high and low
pressures and taking a temperture of the large suction line.
This info in important to troubleshoot. It's either a refrigerant problem
(lack of) or a compressor problem (not pumping properly) or a control
problem...faulty control or safety.......
--
Robb


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