Jeroen

I have seen posting on this problem where the AC keeps cycling the compressor. So does mine. From what I can find on the forum in most cases this is related to the system being low on refrigerant

The AC on my '98 seems to cycle on/off every 5-6 seconds.

The system works reasonably well, so it does cool. But I thought it wasn't that great compared to my other cars, but then again, I'm not sure how efficient the AC is supposed to be.

So I bought one of these refill cans with a gauge. When I hooked it up it showed sufficient filling. So it doesn't appear to be the filling. Instructions on the bottle warn against over filling, so I'm hestitant to give it a shot, put some more in and see what happens

I guess some cycling is normal, or am I mistaken? What are the conditions under which the compressor would run constant.

Anybody with some further insights on how the AC system works as far as the compresso on/off switching is concerned?

Jeroen

DannyH

If it makes you feel better, my '99 does the same thing. I believe it's normal.

hawkfn18

I believe it also kicks on when you use defrost too. I could be wrong.

razor02097

Yes it likely means you are low on refrigerant. When the pressure on the low side drops below threshold a pressure switch tells the computer to disengage the compressor clutch so the compressor doesn't burn up. If you had access to gauges you can actually see what happens. The low side pressure increases, the compressor kicks on, the low side pressure plummets, the compressor kicks off..... repeat

A normal healthy A/C system will have adequate refrigerant to maintain pressure on the high side without the low side pressure getting too low. In other words the compressor should run constantly when the A/C is on.

Other causes is a defective pressure switch, short in a wire, or computer problem (very unlikely).

jth877

Cycling is normal. How much depends on ambient temp and setting.


Here's the FSM testing proceedure:

Review the Service Warnings and Precautions in
the front of this group before performing this procedure.
The air temperature in the test room and in
the vehicle must be a minimum of 21° C (70° F) for
this test.
(1) Connect a tachometer and a manifold gauge set.
(2) Set the heater-A/C mode control switch **** in
the Recirculation Mode position, the temperature
control **** in the full cool position, and the blower
motor switch **** in the highest speed position.
(3) Start the engine and hold the idle at 1,000 rpm
with the compressor clutch engaged.
(4) The engine should be at operating temperature.
The doors and windows must be open.
(5) Insert a thermometer in the driver side center
A/C (panel) outlet. Operate the engine for five minutes.
(6) The compressor clutch may cycle, depending
upon the ambient temperature and humidity. If the
clutch cycles, unplug the low pressure cycling clutch
switch wire harness connector from the switch
located on the accumulator (Fig. 7). Place a jumper
wire across the terminals of the low pressure cycling
clutch switch wire harness connector.
(7) With the compressor clutch engaged, record the
discharge air temperature and the compressor discharge
pressure.
(8) Compare the discharge air temperature to the
Performance Temperature and Pressure chart. If the
discharge air temperature is high, see Refrigerant System
Leaks and Refrigerant System Charge in this
group.
Fig.

Possible Causes Correction
Rapid compressor clutch
cycling (ten or more cycles
per minute).
1. Low refrigerant system
charge.
1. See Refrigerant System Leaks in this group.
Test the refrigerant system for leaks. Repair,
evacuate and charge the refrigerant system, if
required.
Equal pressures, but the
compressor clutch does not
engage.
1. No refrigerant in the
refrigerant system.
2. Faulty fuse.
3. Faulty compressor clutch
coil.
4. Faulty compressor clutch
relay.
5. Improperly installed or
faulty low pressure cycling
clutch switch.
6. Faulty high pressure
cut-off switch.
7. Faulty Powertrain Control
Module (PCM).
1. See Refrigerant System Leaks in this group.
Test the refrigerant system for leaks. Repair,
evacuate and charge the refrigerant system, if
required.
2. Check the fuses in the Power Distribution
Center and the junction block. Repair the shorted
circuit or component and replace the fuses, if
required.
3. See Compressor Clutch Coil in this group. Test
the compressor clutch coil and replace, if
required.
4. See Compressor Clutch Relay in this group.
Test the compressor clutch relay and relay
circuits. Repair the circuits or replace the relay, if
required.
5. See Low Pressure Cycling Clutch Switch in
this group. Test the low pressure cycling clutch
switch and tighten or replace, if required.
6. See High Pressure Cut-Off Switch in this
group. Test the high pressure cut-off switch and
replace, if required.
7. Refer to the proper Diagnostic Procedures
manual for testing of the PCM. Test the PCM and
replace, if required.

Jeroen

Thanks for all the reply.

I filled the system up some more and that reduced the cycling immediately.
Put a whole bottle in, I might need some more, but he compressor at current ambient temperature (70) stays on more or less permanent!

I'll give it a few days/weeks see if it holds its charge before filling up more

Jeroen

djb383

After our a/c overhaul last summer, compressor seldom cycles in warm ambient.....34F at the center vents.

audioal69

Mine seems a little opposite. I added a can of freon and now it cycles like crazy. What would cause this?

Bustedback

Over charge causing high head pressure.

cpenn

On my 01 Cherokee, the compressor used to cycle any time the AC or defrost was on. I bought a low-pressure gauge and found that the low side pressure was fluctuating; likely the cause of the cycles. I added refrigerant, and the compressor stays on constantly with the engine at idle.

However, at highway speeds, I can hear and see on my vacuum gauge that the compressor still cycles on about 15 seconds and off about 3 seconds.

It seems that a lot of people's jeeps cycle like this, but I am wondering if it was designed to cycle like that or to stay on constantly regardless of engine speed, flow rate of air across the condenser, and overall load on the system (ambient temperature, blower speed, etc).

I'm worried about adding too much refrigerant. Should I add more and see if the highway cycling goes away? Is a plugged orifice tube/strainer common, and would it cause these symptoms?

rrich

TO the OP - The mickey mouse gauges in the kits are notoriously wrong.
Get a separate gauge that reads in lbs pressure, not just colors. You can get cheap ones that will do the job.

And - measure it when running, not stopped!

No, it shouldn't cycle until it's down to temperature.

Sounds low, but first tell us the lo side lbs running.

When filling - remember R-134 needs LESS than the original R-12. It's more efficient with greater expansion. The basic rule is use about 2/3 R-134 of what R-12 called out.

Get it running, close windows, AC on high, put a thermometer in a dash vent. Take note of the temp. As you add the temp will drop. At some point it will stop getting colder, then will start back up going warmer. STOP FILLING AT THAT POINT - IT'S FULL!

audio - overfull! See above.

casicua

I am having this problem too. It cycles on and off - but the freon gauge I attached to the service port reading is weird. When the compressor is off, it reads at around 70 PSI, but then when the compressor kicks on it reads at around 20 PSI. Is this normal? Should I be filling it with refrigerant at this point, or is this another problem altogether?

Saprano

[QUOTE=rrich;1686436]TO the OP - The mickey mouse gauges in the kits are notoriously wrong.

Agree !

Get it running, close windows, AC on high, put a thermometer in a dash vent. Take note of the temp. As you add the temp will drop. At some point it will stop getting colder, then will start back up going warmer. STOP FILLING AT THAT POINT - IT'S FULL!

Agree !!! rrich. This was a the first day of 85deg out and the AC was cycling. The kit gauge low side was fluctuating between 40 and 30. giving me the impression low Freon. The temp inside was showing 58deg idling.

I used a gauge kit but I didn't rely on the gauge but used it for filling only and watched the temp inside. I had overfilled and the inside temp was high. So I removed a very small amount to get the temp back down and the cycling stopped. (turned off ac to remove a small amount slowly)

Thanks for that great info rrich ! Oh..I plan on getting a 134a manifold soon.

Alfato

Hi here,

I am new to this forum, as well as my Cherokee ZJ new to me. This is a 2,5 TD an the problem is the compressor running regardless it it has been switched off. The relay is new and inspected what is in the engine compartment. Measured the socket, and all fine by spec. Low pressure switch seems ok. As soon as I turning the key into ignition position the clutch closing, and does not react to the ac on/off button at all. The snowflake disappear, but the connection remain.

Any idea where to check?

I released the gas from the system, because the compressor required a repair.

-ND4SPD-

My '99 does this as well. I'm glad I popped in here to see what the solution is. Seems easy enough.