2G AC Pulsing

[kingje1]

HI all, when I turn my AC on It pulses about once a second. I feel the pull on the engine with every pulse. Coldish air comes out but it's not cold enough to keep me cool in the southern heat.

I'm sorry if this has been answered before, I've been looking through threads and searching now for 30 minutes but haven't found the answer. I am Gen X so forums and tech comes a little harder for me.

Here is what I have done so far:
1. Checked the connections for anything obvious like exposed wires etc and found nothing.
2. Checked the pressure and added until it was good. Air got cooler but still not cold enough.

I've been blessed in the past with cars that have not had issues with AC any more than slight leaks.

I would appreciate any help or a link to a thread that could help me.

 

[kingje1]

Even though my ac is messed up I'm really happy that my car is actually helping me figure this out. The whole time I've had this issue I've never been able to catch it on the gauge or have it happen while idling. Here is what happens on the gauge while pulsing. I 'd love to hear what you guys think about this.https://www.youtube.com/watch?v=UUITCebfjjc

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[pauleyman]

If I had to guess from the high side you barely have enough freon in it to trip the low pressure switch.

Is that clicking we keep hearing the clutch engaging?

 

[waltah]

Wow, certainly does sound like the clutch engaging/disengaging.

A long time ago you mentioned that the idle RPM drops quite a bit when the clutch engages. You also mentioned occasional very high idle RPMs. Because engagement of the clutch and turning on the fans (that happens at the same time) puts a heavy drain on the electrical system it seems possible that it's a voltage drop that's causing the clutch to disengage. The idle should be steady at 750-850 RPM until the clutch kicks in, then go up about 100 RPM.

Turning on the headlights on on high beam should be almost be undetectable, idle speed wise. Same for turning the steering wheel abruptly while idling. Considering the varying idle speed with A/C operation (etc.) I'd bet these tests will fail: The likely cause is your closed throttle position switch (that tells the ECU "you control the RPM now 'cause my foot isn't doing it") isn't working. Figure that out and fix it.

How old is your battery? If it's a few years old and your idle speed drops when the clutch (& fans) come on perhaps it could drop the voltage enough to make the clutch release. Is the alternator belt plenty tight?

Except for the very lucky buyer, close to all just purchased Eclipse/Talon cars have dozens of issues that prior owners didn't deal with. My 'driver' had around 70 problems, the (now running) parts car more than that. Some were small -- light bulbs out in the cluster, right mirror remote adjustment does not work but some were harder -- A/C wasn't working on either one, parts car had no hand brake and timing belt off one notch, driver had bad miss under power. It may take a while to get everything working.

 

[dwb]

Definitely sounds like the clutch is engaging/disengaging constantly after viewing your video. That cannot be healthy for anything, especially short cycling the compressor. You likely have a component failure or even a bad wire or connection.

On my 1g, the things I know will cause the clutch to engage/disengage:
Water temperature switch
AC high pressure switch
AC switch (inside the cabin)
Fan blower switch (inside the cabin)
I think there's a switch inside/near the evaporator under the dash but I've never seen it.
I do not believe there is a low pressure switch, at least on a 1g. I've had mine nearly empty of refrigerant and it still kicks on the compressor and it stays on.
There may be more, but that's all I can think of. Might be worth checking the ground to the AC compressor and the wire to the AC clutch.

I'd start by replicating the issue, then jump your AC clutch to +12v from the battery. Be careful, keep your gauges attached and watch for high pressures and don't let it run like this too long. I bet it runs perfectly.
Put the clutch wire back, and see if the issue reappears. If it does, jumper your AC water temp switch. If it still happens, jumper your AC high pressure switch (like the +12v jumper to the clutch, be careful and watch your gauges). See if eliminating either of those two switches makes it better. If not, see if you can find the switch near the evaporator and do the same.

 

[waltah]

Even though my ac is messed up I'm really happy that my car is actually helping me figure this out. The whole time I've had this issue I've never been able to catch it on the gauge or have it happen while idling. Here is what happens on the gauge while pulsing. I 'd love to hear what you guys think about this.https://www.youtube.com/watch?v=UUITCebfjjc

The behavior of the low pressure gauge is normal for the cycling and the pressures make reasonable sense. I'm betting the high pressure gauge is turned off, either at the gauge set or at the connection to the high pressure line. Turn it on; if it goes up and down in time with the low pressure side and doesn't go higher than 200 PSI or so your A/C system is probably fine mechanically -- you almost surely have an electrical problem.

I would still fix the idle problems before digging into electrical diagnosis. You gotta do it anyway -- a car with an uncontrolled idle speed is semi-undrivable -- and idle speed (and speed control) affect the electrical system in ways that are hard to think through.

 

[pauleyman]

The behavior of the low pressure gauge is normal for the cycling and the pressures make reasonable sense. I'm betting the high pressure gauge is turned off, either at the gauge set or at the connection to the high pressure line.

I got to thinking about this because I couldn't remember. Once the hose it attached and the valve at the fitting end turned the gauge will read regardless of what you do at the manifold. The knows there just determine whether or not that side connects with the center hose and the only time I open high side is during vacuum evacuation.

Turn it on; if it goes up and down in time with the low pressure side and doesn't go higher than 200 PSI or so your A/C system is probably fine mechanically -- you almost surely have an electrical problem.

I would still fix the idle problems before digging into electrical diagnosis. You gotta do it anyway -- a car with an uncontrolled idle speed is semi-undrivable -- and idle speed (and speed control) affect the electrical system in ways that are hard to think through.

 

[waltah]

I got to thinking about this because I couldn't remember. Once the hose it attached and the valve at the fitting end turned the gauge will read regardless of what you do at the manifold. The knows there just determine whether or not that side connects with the center hose and the only time I open high side is during vacuum evacuation.

Right you are, Paul. So it must be shut off at the high side service port. Odd mistake to make since I was actually using the gauge set yesterday!

I spent a few minutes looking at the A/C circuit diagram last night. The clutch is controlled by a relay that's controlled by the ECU. So who knows whatall the ECU might be thinking about when it decides to engage/release the clutch. The pressure switches, and temperature switch (in the compressor) are on the clutch side of the relay -- they are safety devices that are all normally closed when the A/C is turned on.

I think earlier Mitsubishis -- 1G? -- had a third pressure switch that cycles the clutch in normal operation. On the 2G it looks like it's all done by the ECU which gets info from an A/C computer that gets temperature info from the evaporator -- some models of evaporator it's both discharge air and evap. core, others just the core.

The 4G93 engines have a rev. counter in the compressor and they turn off the clutch if it is engaged and doesn't spin as fast as it should. I think this is because the power steering pump is on the same belt on those cars and a locked-up compressor would cause loss of power assist.

Anyway, cycling the clutch on evaporator temperature is better because the high side pressure depends not just on conditions in the evaporator and cabin but also on ambient temperature, car speed, and so on.

 

[kingje1]

Hi Everyone, thank you so much for your posts, for some reason I haven't been getting notifications through email so I didn't think anyone was responding. Here are answers to the various questions posed. Waltah, you mentioned the idle , I recently pulled the throttle body to replace the shaft seals as I had a boost leak. I also replaced the FIAV and ISC o rings. I had to recalibrate the TPS, I used the procedure in the service manual putting the feeler gauge on the set screw and then measuring for continuity and then measuring voltage after I verified I lost continuity and all was well there. When I removed the feeler gauge continuity returned which would indicate it's set correctly. Since then I have replaced the ISC just because I had a spare throttle body and I wanted to see if that made a difference. I have not had any idle issues since replacing the ISC but I also haven't driven the car much because it doesn't have bumpers headlights or AC right now (I am preparing for paint).
The alternator belt is plenty tight, I just replaced it while I was replacing the AC belt and it has about 0.25 to 0.33 an inch of play in the belt.
When I did the video the High side was open at the fitting (turned clockwise until I heard the air swoosh and saw that the gauge started reading pressure)
So right now I know DWB has given me advice to jump the switches to see if either might be bad.
So given the answers to these questions, what should my next step be in diagnosis? Are the switches the likely culprits here? I noticed that the high side pressure is way under the spec that I am supposed to have according to the service manual. Is that just a product of the compressor not staying on long enough to build pressure into the system?

 

[kingje1]

Oh, by the way, Waltah you weren't kidding about people avoiding problems. Even though this car only has 91,000 miles and was bone stock I wondered why I got such a great deal on it. Well, this guy lives in a hotter climate then I live in and it's got a host of other little problems that have obviously been avoided. Some are so easy to fix too. I noticed there was no cruise control so I immediately thought of the clutch switch. Sure enough, it was missing the little bumper, what an easy fix. But the kid was young and he told me he only got it because he was a fast and furious fan. . . Hopefully I will have slightly less than 70 problems with mine. . .

 

[pauleyman]

Unless I missed it how much refrigerant is in it?

 

[kingje1]

When I wasn't getting cold air I put a DIY kit on it and charged it up to between 30 and 40 on the gauge (the green section). I don't know that I can get the compressor engaged long enough to get a good reading on it.

 

[Clipsoe]

What you should do is take it to a shop/ or friend with an AC machine, and let them drain it, and put the right amount in. Or you can refer to these threads for better info.

https://www.dsmtuners.com/threads/resolved-a-c-refrigerant-capacity.343157/

https://www.dsmtuners.com/threads/ac-system-pressure.513204/

 

[kingje1]

I returned the loaned gauges and bought some of my own and hooked them up. Here is a video of the readings I'm getting now and here is the chart from the service manual.

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[kingje1]

Here is a video of the idle speed while the ac is onhttps://www.youtube.com/watch?v=Cz0mKy-axEM

Ok, I don't know if that worked or not. Here is take 2

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[Clipsoe]

Well according to the chart, and ambient temps, which for Nashville was 95 F today. The low side shouldn't be over 32psi. Your low side seems to be hitting 50 psi. You probably have too much freon in the system. That usually happens when you use those auto part store charging gauges. Evac the system, vacuum, the charge with the appropriate amount which is 26oz's.

 

[kingje1]

Correct me if I'm wrong but aren't I taking the measurement when the compressor clutch is engaged? When the compressor clutch engages the reading goes to 25psi on the low side and when it kicks off it goes back up to 50.

 

[Clipsoe]

Ok lets try this. How many ounces of freon is in your system currently?

 

[wrencher]

That is a pretty rapid cycle of the clutch.
Your going to need to test the a/c clutch relay control circuit.
The relay in the underhood fuse box provides power to turn clutch on.

The relay itself is an electrically controlled switch.
Your going to have to get involved with some diagnostics here to accurately diagnose this..

Your going to need a real manifold pressure gauge and the proper charge amount to be certain running pressures are not off.

The wiring diagram can explain the architecture of the complexity of this circuit. It would be a quite a write up how to check the a/c ecu , dual pressure switch ,a/c temp switch evap fin sensor etc...
Need to know why the relay is being pulsed like that .

So of the top of my head either its way overcharged or the system is restricted causing insanely high side pressures causing the dual switch to cut it in and out .

Or the thermo fin sensor in wonky.

but this will take some knowledge and proper tools to diagnose quickly. I dont suggest the throw parts at it method.

I suggest some prep and study on your part or take it to a professional who is good with electro- mechanical a/c issues.

 

[kingje1]

That's exactly what I want to do, get a good diagnosis. I don't know anyone who's really good with electro-mechanical a/c issues. Does everyone agree I should evacuate and refill the system? I know Clipsoe does. I haven't really wanted to do this because it seems to pass the service manual performance test with flying colors. Both low and high side pressures are within spec and the air is nice and cold. I do agree, however, that the heavy draw on the system like Waltah mentioned would explain the drop in engine RPM when the clutch kicks in and maybe it keeps kicking back off because it's working too hard to get the refrigerant through. I found the dual pressure switch test procedure in the service manual which looks pretty easy to perform. Wrencher, what is the thermo fin sensor?

So of the top of my head either its way overcharged or the system is restricted causing insanely high side pressures causing the dual switch to cut it in and out .

Would those insanely high side pressures show in the manifold gauges? I'm not getting insanely high on the manifold gauges?

 

[waltah]

That's exactly what I want to do, get a good diagnosis. I don't know anyone who's really good with electro-mechanical a/c issues. Does everyone agree I should evacuate and refill the system? I know Clipsoe does. I haven't really wanted to do this because it seems to pass the service manual performance test with flying colors. Both low and high side pressures are within spec and the air is nice and cold. I do agree, however, that the heavy draw on the system like Waltah mentioned would explain the drop in engine RPM when the clutch kicks in and maybe it keeps kicking back off because it's working too hard to get the refrigerant through. I found the dual pressure switch test procedure in the service manual which looks pretty easy to perform. Wrencher, what is the thermo fin sensor?

Would those insanely high side pressures show in the manifold gauges? I'm not getting insanely high on the manifold gauges?

Too high pressures would indeed show on your high side gauge. Follow that refrigerant line from the high service port back to the dryer cartridge: The thing sticking out of it to which the harness connects is the dual pressure switch (too low or too high turns everything off).

At this point you have an A/C symptom -- clutch sometimes cycles on and off rapidly. We do not know if that is an A/C problem or if the problem is somewhere else. Since you have an idle speed control problem and it may be that the ECU (which controls the clutch relay) is smart enough to disengage the clutch when the idle gets too low, I would diagnose and fix the idle speed control first. Then look at the A/C situation again.

 

[wrencher]

So your problem is intermittent... That definitely says an electrical issue.
I posted info on 2g turbo a/c here

https://www.dsmtuners.com/threads/2gb-ac-circuit.517652/#post-153689500

Not the same issue in that thread but a/c compressor clutch circuit info none the less.
There is quite a bit of info others posted here in this thread as well.


You need to Test what is making the a/c relay to be controlled like that, unfortunately testing only while the condition is occurring.

I suggest to study the diagrams and test the components.
Take your time and confirm proper terminals wire color etc.
The OEM diagrams lay it all out once you get used to it testing will come easier.

 

[kingje1]

Waltah, thanks for the info, I took what you said and took the car out to test the idle. Since I had changed the IACV I hadn't tested to see if it fixed my issue or not so this gave me an opportunity to do so. Previously, the car would idle a little higher than normal while cold, then it would warm up and I would get an idle somewhere in the 1300 to 2300 range. I just did quite a bit of driving and I've now got perfect idle. Once the car warmed up I tested the idle speed after every stop and sure enough. The idle would slow while the clutch was in and then drop down to about 800. This happened like clockwork every single time. I still have continuity when the throttle is closed so my TPS is correct and the voltage with the .177 feeler gauge is only like 0.73 volts so it is definitely within spec. I turned on the AC while was driving and it immediately started pulsing. I think the change of the ISC has taken care of my throttle issue. When I was changing the ISC, I did a test by cycling the ignition. On the old ISC the plunger just rotated slightly, on the new one is moved in or out with the cycle so I am pretty sure the old one was bad.

 

[kingje1]

Wrencher, thanks for the info. I have looked through the service manual several times to see what I can test for but your post and link caused me to take a better look. After I was testing the ISC and I got back home, I wanted to test the idle when turning on or off the AC, well, I couldn't get the compressor clutch to engage at all (again, it being an intermittent thing maybe an electrical issue). So I found this chart and I am going to attempt to test for the conditions that would indicate the compressor should be on. Please have patience with me as I am expecting a call any day from the body shop for me to bring the car in for paint.

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[kingje1]

I want to thank everyone for their help so far. I started testing down the line here but unfortunately the clutch was kicking in so I couldn't diagnose why it wasn't the other day. So I did test the dual pressure switch and while I was testing it according to the manual it started pulsing again. The whole time the switch maintained continuity so I can definitively rule out the dual pressure switch as being an issue. That brought me to the AC compressor relay. My thoughts are that this can really help me to figure out if there's an issue. The pulsing is caused by the rapid engaging and disengaging of the clutch, I would assume that the signal to make that happen is coming through the relay. I studied the diagram below and I feel like I may be able to isolate where I am losing the clutch engage signal somehow but I need some help from someone who is electrically inclined.
From the post that wrencher gave me I can jump sockets 4 and 5 to make sure that they engage the clutch, if they do that part of the circuit is good.
Then I need to test socket 3 which will tell me if I have voltage making it all the way through from the switch through the Auto compressor ecm, the dual pressure switch, the ac refrigerant switch and the ECU. Here is where I am murky. Do I test for voltage using chassis ground or should I use socket 1?
I am assuming that if one of these components is bad the voltage will come and then disappear and come again here at this socket. I guess what I don't know is how I would know if the socket is good? We don't know what causes the pulsing and it's intermittent.
Also, How do I test for ground at socket 1?

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[wrencher]

The A/C relay field coil is provided a power and a ground thru terminals 1 and 3.
Power and ground excite the relay coil and the electromagnetic feild produced by the coil close the contacts of the relay completing/engaging the intended circuit.

So ensure the coil side is provided a power to one terminal or coil 3? and a ground to coil terminal 1.
With the relay in place and say its missing the ground....
it will have power through out whole circuit in testing.
On terminal 1 and 3
Now vice versa with the relay in place and say there is no power and the circuit will have a ground thru whole circuit.

This of course is with the a/c relay being commanded on by the control of the a/c ecu and the engine ecu.

Need to find which one is "pulsing" the relay on off rapidly and it will narrow down what part of the relay control circuit is your culprit.

Very doubtful its a bad relay usually they fail open/never operate.
Its a safe bet your issue lies in the relay control circuit.