AC Clutch is engaging then disengaging [Archive] - FSB Forums

: AC Clutch is engaging then disengaging


az84bronco
10-02-2009, 11:43 PM
My 84 Bronco 's A/C clutch is engaging then disengaging. The voltmeter read a steady 12+ plus volts when running and the wiring harness is removed, once the wiring harness is connected to the compressor, the voltage drops from 12 plus volts to zero, while the clutch engages and disengages. I know there is a low pressure thingy somewhere, but I am wondering if the problem is the relay, the clutch, the compressor or the lack of refrigerant that is tripping the low pressure relay causing the AC clutch to engage then disengage sporadically.
Not an A/C mechanic,
James-n-AZ

stan the man
10-03-2009, 12:29 AM
Usually it means you're out of freon.

Poorboyz
10-03-2009, 01:31 AM
not out but low on freon OR there could be blockage somewhere in the system that triggers the high pressure switch and cause the clutch to disengage then engage when the pressure drops a bit. Is it cycling 3 seconds on 3 seconds off? Most likely though it's low on Freon but you won't know for sure until you hook up some gauges to it. One quick way to know if it's low on freon or it's a blockage in the system is when you have the gauges hooked up and if one of the needles vibrates then it's a blockage, if it doesn't then it's low on freon.

Hope it helps.

rhauf
10-03-2009, 01:36 AM
Add freeon, R-12 if it's stock, or R-134 if it's been "converted" (converted just means had the old r-12 evacuated/let out completely, and charged with 134a, you cant mix them)

i'd say you need at least one can. if it goes low right away again, look for oil/gunk around the a/c fittings, it could indicate a leaky O-ring. but it is normal to have to recharge every few years.

Poorboyz
10-03-2009, 01:38 AM
I would not add freon until you put gauges on there to check proper pressure in the system. I also don't think it's normal to have to add freon every few years...seems if you have a leak then get it fixed until the system holds pressure then pull vacuum and charge the system.

rhauf
10-03-2009, 03:14 AM
well i'm not claiming to be an expert, but i have heard from an expert (or at least an a/c shop) that a certain amount of loss every year is normal (dont remember how much) and if the truck has never been recharged.. well, 1984 is a long time ago.

i know gauges should be used, but i've never used them and i've had pretty good luck just guessing w/ a/c systems in several vehicles, 3 broncos, an f-150, 2 chevy trucks, a suburban, an old mercedes, my explorer, and some others.

my method is to charge it until at about 1700 rpm it doesn't click on and off with ac on high.

rla2005
10-03-2009, 09:48 AM
The clutch is supposed to cycle on and off. It should never stay on 100% of the time. Depending on the outside temperature, humidity, refrigerant level and the interior temperature the cycling will shorten or increase. Your voltage measurements sound correct. You really need to put some gauges on to determine if your pressures are in range. Do a search on this site, there are several thread topics discussing the correct pressures and how to determine if someone has converted the a/c system over to R-134a.

Every a/c system does leak to some degree. The advent of hoses with liners (barrier hoses) and modern o-rings materials slow the leakage down to an acceptable level. The OP's Bronco looks to be a '84. That is borderline whether or not his truck came from the factory with barrier hoses. This can accelerate the leakage due to their design and age if they are not the barrier type. If a PO had converted to R-134a without changing the hoses to the barrier type the leakage can increase because the molecules are smaller for R-134a versus R-12.

A cheap and quick way to check your a/c is to place a thermometer in the center vent, let the truck run for 10-15 minutes at normal idle. The vent temperature should be in the 30-45 degree range if the outside temperature is 65-85 degrees. If your vent temps. are good that indicates the a/c system is probably running inside it's design limits. If the vent temp. is above that, your are probably low on refrigerant. Other factors could also be the root cause, but it will require a manifold gauge set to view the high and low side pressures to properly diagnose.

In my opinion a blind charge procedure as outlined in a previous post is very dangerous to the the operator and the vehicle. No offense, but that procedure is well outside my comfort level. Get the right tools for the job. A quick reading digital thermometer and a manifold gauge set can be found for less than $50 USD. It will pay for itself in a very short amount of time.

Camo Horse
10-03-2009, 10:15 AM
I agree with the last statement. Your A/C compressor is supposed to cycle on and off, if your compressor kicked on and stayed on, then there is two problem, one is it not supposed to stay on constantly with could be a cause of low pressure with the freon level, and two being that the clutches and compressor would burn up and not work any longer.

So if you are stating that you are witnessing the cycle of on and off, then that is the way it is designed to work. It is just maintaining hi pressure. The only proper way to determine if it is low on freon, is to attach a guage to the port, and start the vehicle and turn off all accessories and turn the the a/c on hi. Allow it to run 5-10 minutes to allow a few cycles. then measure the high and low psi. This can be achieved by going to a auto parts store and picking up a combo kit with has the guage, freon, and the necessary adaptors if needed to measure the psi levels at hi and low for around $20.00

When you attach the guage to the pressure line, the compressor will continue to cycle allowing you to see the hi and low pressure readings. When the compressure kicks on, it will measure the low pressure, which should be no less than 25 psi. When the compressor kicks off, then the hi pressure should read no higer than 45 psi.

If you over fill the a/c system, then the high will register above 45 psi and could cause blown seals and ultimately leak constantly. If when it goes below 25 psi on the shut down of the clutch, then it is low and should add as needed to maintain a constant 25 psi.

And the answers of the cycling of the compressor is caused from low freon is totally incorrect.

az84bronco
10-03-2009, 11:18 AM
Thanks for all the info and help. Here is a little more detail in the problem. The clutch is engaging then disengaging sporadically about every few seconds and if I let it run for a several minutes, it starts to smell like burnt clutch. The air coming out of the vents at first is cool, not cold. The truck was converted to the new stuff in 2000 when the compressor was changed out (40,000 miles and 9 years ago). I do not have any other docís on if and when it was serviced after that. I will head over to Checker Auto and maybe Harbor Freight to get some gauges and some freon.

rhauf
10-03-2009, 01:46 PM
Thanks for all the info and help. Here is a little more detail in the problem. The clutch is engaging then disengaging sporadically about every few seconds and if I let it run for a several minutes, it starts to smell like burnt clutch. The air coming out of the vents at first is cool, not cold. The truck was converted to the new stuff in 2000 when the compressor was changed out (40,000 miles and 9 years ago). I do not have any other doc’s on if and when it was serviced after that. I will head over to Checker Auto and maybe Harbor Freight to get some gauges and some freon.


I'd say it's likely that the filter is likely clogged. it could also be a bad oraphice (sp?) valve. the filter is that in-line filter between the compressor and the condenser.

yeah my ways of doing it are a bit redneck, but my philosophy towards a lot of this kind of thing is, if you make it into too big of a job, requiring a bunch of tools you don't have, it'll never get done. i for one know none of my vehicles would have working A/C if i had to buy a bunch of expensive gauges and other equipment to do it, or if i had to take it to a shop and pay a bunch. i also don't evacuate the air from the system after assembly, i know i know, not kosher. at idle, on a hot day, the A/C pump will usually run constantly with the fan on high, if it's fully charged. at least it does for me. when the rpm increases the pump will begin to cycle.

my a/c is ice cold even when it's 100+ here (which is often in this valley) and it seems to keep working. yeah, it's not the right way to do it but it works. i'm just saying, that if/when it comes to either abandoning you're a/c system for lack of available tools to do it "right" or doing it my way, you might as well give it a shot. most of the people who have non working a/c probably could have it working easily if were willing to try it my way. instead no a/c

if you have access to the gauges, or are willing to buy them, then use them.. it's the way to go... if not, i'd change the filter and the oraphice valve and recharge it.

az84bronco
10-03-2009, 01:48 PM
YAY! All fixed. I went to Checker, got a big can of R-134 with lube and conditioner added for $24.00. It included a gauge. The gauge read between 22lbs-30lbs. When it would drop below 25lbs the clutch would disengage, then it would go up to past 25lbs and kick back on. I added enough R-134 to get it up to 35-37lbs and it is steady, clutch engaged and blowing ice cold air.
Good Times and thanks for all the input!
:beer

rhauf
10-03-2009, 11:07 PM
awesome! thanks for the update. it's always a let down when you help somebody out or give advice, and they "dissipear" .... i think they get it going and never bother to come back. or who knows.

themike
10-07-2009, 10:48 PM
using the right tools is important. I do hvac repair for a living and have seen people hurt by an over charged system. the owner just add liquid with no gauge, when we got to it a guy was about to put his gauges on and a line broke blowing hot r-22 on his arms. you could get frost bite or burned by this stuff. BE CAREFUL.

slim68
10-08-2009, 03:34 PM
if you do not know what you are doing with the climate control system, take it to some one who does.