a/c compressor cycling on/off rapidly

[anarky321]

1998 Ford Explorer Sport

situation: a/c compressor cycles on/off rapidly - 2/3 seconds -on and off forever while the a/c is turned on. when a/c is turned off the compressor just freewheels normally.

what i have tested: low pressure cutoff switch - i jumped it and nothing changed, compressor keeps cycling on/off, pressure on the low side was tested with a gauge - about 50-25psi at startup then the pressure grows as the car keeps running, up to 80+psi , voltage at the compressor plug is a steady 13.1x volts while the car is running, this is tested with the voltmeter between the wires with the harness off, voltage at the low pressure cutoff switch is also a steady 13.1x volts, also tested while the plug was taken off, there is continuity between the 2 terminals of the compressor - ~.5 ohms, doing an ohm test from either terminal of the compressor to frame does not give continuity, not sure if that means anything, the WOT relay clicks every time the compressor comes on and off, the A/C 15A fuse is good, i tried switching the WOT relay with the identical one next to it, no difference in operation, i think it was the PCM relay

the a/c does not blow cold air, ever, i have not been able to get the A/C compressor to engage for more than 2 seconds under any conditions, i have NOT tried jumping the A/C compressor directly from the battery and im not even sure how to, is that even necessary given that there's a steady 13.1V on the harness going to it?

edit: where is the high pressure switch located? since the voltage at the compressor is a steady 13.1V doesn't that automatically mean that the low/high pressure switches are not the issue?

 

[budwich]

well.... the WOT relay should not be clicking. That is most likely what is causing your compressor to go on and off.... likely at the same rate of the "click".

having said that.... your method of testing for voltage is "fubarred". Voltage is ALWAYS measured to a known ground. Measuring across two wires doesn't really tell you anything UNLESS one of them happens to be a ground.... which I think in your case ain't true.

 

[anarky321]

so the circuit inside the compressor doesnt ever get interrupted right? the clutch engaging and disengaging is only a function of the voltage across the stator but its always a closed circuit?

edit: the 2-wire connector at the back of the compressor - one green w/ red stripe and one red - is the compressor connector right? because i looked at it again and it almost looks more like a high pressure cutoff switch the way its located; i want to make sure im not testing voltage across the high pressure switch by mistake

and the WOT relay is definitely clicking every time it turns off and ive tried 2 different relays on it already so the relay is not the problem

 

[budwich]

when ever the wot operates, that will kill the circuit to the compressor. In general, I would say that if it is operating regularly, you have an issue with what the PCM "thinks" your vehicle is doing at the time... running to slow, running to fast, or overheating.... just a guess.

PS. there is "nothing" inside the compressor to interrupt the electrical path "directly".... other than a failure / broken wire.

 

[anarky321]

OK UPDATE

what i was testing was the high pressure cutoff switch, im 99% certain, there is another connector at the compressor which is VERY hard to get to and i cant even take it off its so awkwardly placed which i think is the ACTUAL ac compressor power connector

i jumped the high pressure switch and that made no difference so both pressure switches have now been jumped, i will now attempt to get to the ac connector, take it off and monitor the voltage on it during the cycling, does anyone have any suggestions on how to take it off? is it one of those spread outward clip connectors? shouldnt the voltage actoss the high pressure switch go to 0 when the WOT relay clicks on and off?

 

[anarky321]

2nd update: with the engine running and a/c switch on full the voltage at the ac compressor is 12.85V steady, the relay does not click when the connector is unplugged, i havent tried to jump the ac compressor connector yet, should i?

if anyone else has trouble getting the compressor harness off, i had to do it from underneath driver's side reaching up below the ac compressor to pull the clip outward enough for it to snag so i could get the connector off from above, not easy

just for clarification:

the high pressure switch is round, is on the back of the ac compressor and has a green w/red stripe and a red wire going in - 2 wires, round connector, back of the ac compressor

the ac compressor switch connector is rectangular, located right by the pulley on the right side of the compressor and has a black wire and a black w/ yellow stripe wire going in - 2 wires


edit: what im settled on right now is that for some reason the WOT relay is getting energized, so the PCM thinks that the engine is at WOT, i have to mention that the TPS sensor set off a code about a month ago but hasnt since and i tested the TPS sensor today and the resistance on it cycles up and down smoothly, no breaks etc.

is there any way to bypass the WOT relay out of the ac circuit?

 

[budwich]

like the other switches, the "switched contacts" of the relay can be wired / shorted for continuity.

 

[anarky321]

i tested the voltage on the WOT relay, 12.8V steady on both 85-86 which are the left right pins and 87A-30 which are the middle-bottom pins, the top pin 87 is not used in this circuit

which ones are the control voltage and which ones are the actual load pins? ie which ones am i shorting to keep the circuit closed? im guessing one of the sets is pcm to ground circuit? am i shorting 85-86? or 30-87A?

i also tried revving the engine up and down and that doesnt change anything so i doubt my tps sensor is to blame here for sending a bad signal to the pcm

also is the WOT relay fundamentally different from the 2 other relays next to it? what should the number written on it be? i have 2 relays with identical numbers on them and 1 with a different number - fuel pump and pcm i think are the other 2 - are all 3 of them "normally closed" relays?

edit: in the Haynes manual is says the PCM signal terminals on the PCM for the WOT relay is 69 pink/yellow and 41 green/orange but it doesnt say which pins on the relay those go to

would i blow a fuse in my multimeter if i try to measure current over the main circuit pins? how much current flows through the ac circuit at full load? this is the first time ive had to use a multimeter but im pretty sure the max this can handle is 10A, it says "10A/15sec MAX each 15 min UNFUSED" - does the AC circuit have more than 10A going through it at full load?

 

[anarky321]

I GOT THE COMPRESSOR TO STAY ON

i had to jump the WOT relay 87A to 30 and then i had to jump the low pressure switch

having both of them jumped the compressor stays on, i shut it off so it doesnt seize up or anything, will test with a gauge in a few seconds to see what the pressure is on the low side while it spins

 

[anarky321]

tested the pressure with the compressor on - about 10psi, obviously far below normal which is why the low pressure switch had to be jumped, still not sure why the WOT relay is energizing

i noticed there is a relay diagram on the side of the relay which shows that 85-86 are the PCM signal pins - .3A and 87A-30 are the circuit pins - about 3A at key turn

i took the jumper off the low pressure switch, going to get some refill cans tomorrow put them in see what happens, i probably have a leak somewhere in the system

in the end all it took was a paper clip and a safety pin to get it to work =)

 

[anarky321]

went to walmart, filled it with 2 bottles of R134A, A/C now WORKS, and is very cold

pressures are good, will check in a day or two to see how much if any leaks out

the low pressure switch is no longer jumped and is keeping the compressor on since the pressure is above 30psi

WOT relay is still jumped with a safety pin =/ whatever it takes

 

[budwich]

well... you solved your AC problem BUT it would appear that you might have another "onion" in the system with the WOT... good luck, stay cool .... odds are your TPS isn't doing what the PCM "thinks".

 

[jonfal]

Anarky321, I am having an identical problem, with the compressor clicking on and off repeatedly when I am at an idle (runs fine once I hit 2k RPM).

I ended up finding a bad relay (I think 46A or B in the distribution panel), and that got my compressor to at least try to work.

I have read about the WOT relay, and see it on the electrical diagram in my Haynes. However, it shows the relays as jumping 69-41 with pink/yellow in 69 and drk green/orange in 41. Was it pretty easy to locate your plug #s once you removed the PCM? I'm a bit of a novice when it comes to electrical issues, but I can certainly use a paper clip to test this once I know I'm headed in the right direction!

Also, is the WOT relay in the distribution panel under the hood? If so, does anyone know if the WOT relay and the A/C Clutch relay are one in the same?

 

[ThePhoenix]

this is over my head i think. I am not sure what a WOT is

I filled my a/c with two cans...still not ICE cold...blows better after 4-5 minutes

the cycling on mine slowed when I first put cans in...now it seems more frequent again...so I am guessing I have a small leak

 

[anarky321]

WOT relay is a separate relay in the relay box under the hood, i just took the relay completely out and jumpted the north and south pins if i remember correctly with a thick paper clip and that was it, then of course you have to make sure your refrigerant levels are normal

 

[jonfal]

Anarky, I was afraid you would say that. I have looked in the Haynes and in my Ranger owner's manual, and the only mention of that relay is a picture in the Haynes that is for an earlier model than what I have, and the distribution box (or the fuse/relay box under the hood) is different and does not reference a WOT relay.

Do you remember what position number the relay was in when compared to your owner's manual diagram? For instance, I have 46A/B and 48A/B which are the fuel pump, wiper pump, fog lamp, and A/C clutch relays that are 4 separate relays of the same type. There are 2 larger ones, one for the PCM and one for something else I can't recall, but isn't related to the WOT, A/C or anything pertinent.

 

[William Gareau]

1998 Ford Explorer Sport

situation: a/c compressor cycles on/off rapidly - 2/3 seconds -on and off forever while the a/c is turned on. when a/c is turned off the compressor just freewheels normally.

what i have tested: low pressure cutoff switch - i jumped it and nothing changed, compressor keeps cycling on/off, pressure on the low side was tested with a gauge - about 50-25psi at startup then the pressure grows as the car keeps running, up to 80+psi , voltage at the compressor plug is a steady 13.1x volts while the car is running, this is tested with the voltmeter between the wires with the harness off, voltage at the low pressure cutoff switch is also a steady 13.1x volts, also tested while the plug was taken off, there is continuity between the 2 terminals of the compressor - ~.5 ohms, doing an ohm test from either terminal of the compressor to frame does not give continuity, not sure if that means anything, the WOT relay clicks every time the compressor comes on and off, the A/C 15A fuse is good, i tried switching the WOT relay with the identical one next to it, no difference in operation, i think it was the PCM relay

the a/c does not blow cold air, ever, i have not been able to get the A/C compressor to engage for more than 2 seconds under any conditions, i have NOT tried jumping the A/C compressor directly from the battery and im not even sure how to, is that even necessary given that there's a steady 13.1V on the harness going to it?

edit: where is the high pressure switch located? since the voltage at the compressor is a steady 13.1V doesn't that automatically mean that the low/high pressure switches are not the issue?

 

[Pete Deering]

I should like your system is low on freon. That is normal for a system to operate. What is your high side pressure? What is the center vent temperature? You stated you added to cans of Freon, and now its working. The system a little over charged, But you have a small leak and the system Will come down in range. Note as your system losses Freon, you also loss refrigant oil.