I'm hoping someone can point me in a better direction. My A/C is short cycling (on/off about every 10 seconds) even as you first turn it on. Seems to cycle quicker when rpm's are above idol (ie truck moving). Took it to 2 different shops and both said it's not because of low freon. One shop removed and replaced freon to the correct level. Both shops said it's cycling at the correct pressures. I even replaced the A/C cycling switch. Is there anything else which causes the compressor to cycle (vacum, temp. gauge in cabin,...?) Concerned about compressor/clutch breaking w/ this many cycles. New truck to me but has ~80K miles. (2000, 2wheel drive, 3.0L Flex, ~80K miles)

 

A partially clogged orfice tube could cause that symptom by not allowing enough liquid refrigerant into the evaporator core thus allowing the compressor suction to rapidly lower the low side pressure to the cycle off point.

 

I'm pretty handy, but where is the orifice tube located? Can it be replaced without evacuating the system? Is it something that a handy person can do?

 

Its in the line between the output of the condenser and input of evaporator. Requires removal of refrigerant, replacement, and re-evacuation/recharge of system. Most times replacement of the accumulator/dryer is also required since the disintegration of the desiccant bag lets the desiccant particles flow through the system. Since the orfice tube screen has the smallest openings in the system, thats where all the stuff gets caught. Sounds like you need to take it to a GOOD automotive A/C shop that knows what they're doing to get an evaluation.

 

I'm not sure if the ranger have this but, my old silverado has a screw thats in between the 2 contacts of the pressure cycle switch. Pull off the connector and take a look. If it does. dont go too crazy because then it wont cycle at all and can jack up your system.

 

Check the A/C Clutch Cycling Pressure Switch located on top of the Accumulator.
(round with two wire connector on end). Remove connector, jumper the contacts in the connector. If the compressor stops cycling, you found the cause.
Was the fix on my '97. Think the replacement about $15 at AutoZone.
Simply remove the old and replace it-no R34 will be lost.

No expert but hope this might help

Irv

 

His initial post indicated he'd already replaced the A/C cycling switch and it didn't help. A defective High Pressure Cutout Switch (HPCO) could possibly cause "short cycling" but it would have to be opening at pressure near the normal "high side" pressure operating point (unlikely) rather than its design operating point of around 390 psi.

 

You really need to see what pressure it is cycling at they shouldn't cycle until the pressure get down to about 20 psi give or take a few psi. the idea is to keep the evap temp above freezing so it doesn't freeze off. And if it is cycling that quick then it is either low on freon or the orffice tube is plugged or the acummulator is plugged causing the low side to go to low. If the switch is cycling at to high a pressue either replace the switch or adjust it via the screw that is in the center of it that you can only see when it is unplugged. And i don't remember which way to turn it for increase or decrease.

 

Another possiblility is that shop that recharged it, may have overfilled it or didn't fill it all the way. Go to walmart and buy one of those gauge kits for about $15 thats checks the freon level. Make sure when you check it the truck has been running with the A/C on for at 5-10 minutes. The kit comes with a pound of freon, but you dont have to crack it open to check the pressure.

 

Doesn't sound like an overcharge problem to me but if you suspect it is, let truck sit overnight so everything is at ambient temperature. Engine off; measure refrigerant pressure- it should be around 90 psi at 80 deg. F. A little more for higher, less for lower temperatures. This is a quick/easy check that doesn't depend on cycling pressures, rpm, and all the other variables.

 

Thanks guys for the suggestions. From all the symtoms and what you folks are saying, I'm really leaning now toward the orifice tube being stopped up. That unfortunatly is is a $200 job for $2 part. I guess I continue to baby it for the foreseeable future.

 

Got a problem with that myself. 95 Ranger 3.0 V6, 68K miles - little/no cooling, compressor cycling 10 seconds or so, changed the low pressure switch, jumping the low pressure switch causes the compressor to run constantly. Is this the feared clogged orifice tube?

Thanks!

 

You need to post your suction/head pressures as well as ambient temp. Take readings with the engine at around 1200 RPM and the fan on high. This is the first step in diagnosing what initially has the inklings of being an undercharged system.

 

As much as I hate to admit it, I did just decide to ignore the worthless gauge on my recharge kit and fixed the A/C cycling problem by hooking the R134a can to the low side and jumping the low-side switch with a paper clip to kick the compressor on long enough to pick up enough refrigerant to stay on and recharge properly.

When I had tried before there was no perceptible charge getting into the system and the cheap gauge was reading all over the dial inconsistently such that I could not figure out if the system was charged or not. Now back to 45-degree AC.

Not the right way to do it exactly, but it bums me to shell out for all new high-end gauges while looking at my perfectly good and expensive R12/R22 set.

 

You can buy the replacement ends (about $15 apiece) to allow your expensive set to hook up to the quick connect r134A ports and the temp/pressure charts are avaiable on the web. And they have the end to get from 1/2 acme to 1/4 flare so you can hook up to the cans or the drums.