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89 Ranger a/c clutch cycling at idle speed


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RangerGuy
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Jun 12, 2011, 10:41 AM

Post #1 of 23 (3678 views)
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89 Ranger a/c clutch cycling at idle speed Sign In

Hey - any advice you can give me on my a/c problem will be greatly appreciated.

I will give as much information as possible so hopefully it will make this easier to diagnose.

1989 Ford Ranger
Engine: 2.9L V6
Trans: Manual 5 spd.
104,000 miles original motor and trans.
A/c is original from ford not aftermarket add on.

In 2000 a/c converted to r134a by a professional technician.

Current problem: With a/c on Max, fan blower on high and engine at idle the a/c clutch cycles off and on about every 3 seconds. When the clutch engages the motor stumbles a little and the rpm's dip to about 700-800, when the clutch disengages the rpm's go back to about 1000 which is a normal idle for this truck. At this point the vent temp is hot, about 80 plus degrees.

If you throttle up the engine to about 1500 rpm. the a/c compressor clutch will engage and stay engaged like you would expect when operating normally. So basically as long as the truck is at 1500 rpm's you have a/c, any lower rpm and there is no a/c. At 1500 rpm or higher the vent temp is around 68-70 degrees on a day with outdoor air temps around 95 here in Ga.

When I put my gauges on it while holding the rpms at 1500 the low side pressure is about 40 and high side is about 300.

I used a wire to bypass the low pressure switch at idle rpms 1000 and the compressor continues to cycle on/off about every 3 seconds. That is where I got confused because I thought I had a bad low pressure switch but obviously that wasn't the issue.

I have looked all over for a high pressure switch and cannot find it, if it even has one.

This truck has a belt driven radiator fan so it runs all the time. I also visually inspected the condensing coil and didn't see a lot of junk on it so I don't think it is an air flow problem, but I could be wrong.

I'm a pretty experienced at doing my own a/c work but I'm not all that great at hunting down some electrical issues which is what I think this might be, but I'm not sure.

Any help you can give will be greatly appreciated, it's hard to sit at red lights in Ga with no a/c on these 98-100 degree days!


Hammer Time
Ultimate Carjunky / Moderator


Jun 12, 2011, 11:04 AM

Post #2 of 23 (3670 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

What you need to do is monitor the voltage at the clutch to determine if the power is cycling on and off to the clutch. This could just be a case of a weak clutch coil and the higher RPM bring higher voltage to the clutch.




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



RangerGuy
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Jun 12, 2011, 2:15 PM

Post #3 of 23 (3659 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

I checked the voltage at the compressor with the engine at idle, a/c on max, blower on high.

When I first start the motor with the a/c on the clutch engages and there is 12 volts at the compressor. The clutch stays engaged for about 1 minute before it starts cycling off and on. When it starts cycling there is not 12 volts at the compressor anymore. The voltage displayed on my meter that is attached at the compressor starts spiking up and down with the cycling of the compressor. It spikes so fast my digital meter can't really get a reading on the voltage anymore. I may have overestimated how long the clutch remains engaged when it cycles. It only remains engages for about 1 second and it keeps cycling very fast like this until I turn off the truck.

Any ideas on what I should check next? I don't know where the a/c control switch or high limit switch is located but if you can point me in the general direction I will check those too.

Thanks for the help so far. I know this is just a process of elimination until we figure it out!


Hammer Time
Ultimate Carjunky / Moderator


Jun 12, 2011, 3:08 PM

Post #4 of 23 (3647 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

You're going to have to troubleshoot at the WOT relay to see if one of the signals is dropping out there. It could be possible to have an open spot in the TPS causing the relay to cut out or a problem with the relay itself.

The relay is in the power distribution box.






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RangerGuy
User

Jun 12, 2011, 6:07 PM

Post #5 of 23 (3636 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

I located the WOT relay and I did some testing and thought I found a weak relay so I put a new one on it for 13 bucks.

Unfortunately, that didn't solve the problem so my testing skills must have been a little off. With the new relay installed the compressor still cycles while the engine idles. I checked the voltage on the new relay terminals and I get about 12 volts when the clutch is not engaged and then the volts go to zero when the clutch engages for about one second and this voltage spike continues as the clutch cycles off an on. I'm really not sure if that information helps or not but I figured I would include it just in case.

Since you mentioned the TPS could be faulty I started paying closer attention to the engine idle speed. I started the truck with the a/c off and it idles about 800 rpm. As soon as I turn the a/c on the clutch starts cycling but the engine rpm's do not increase. I never really noticed this before but it seems like the TPS should be increasing the rpm a little, but maybe not. If I hold the throttle down and run the rpm's up to 1000 the cycling will stop and the a/c seems to work normally.

I would like to troubleshoot or replace the TPS but i don't really know where it is located either.

Thanks for your help so far that wiring diagram was excellent!


Tom Greenleaf
Ultimate Carjunky / Moderator


Jun 13, 2011, 2:19 PM

Post #6 of 23 (3623 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

Ranger: Short read and am behind here and who knows where out there. Check clutch air gap. Don't even need tools - just use a standard biz card which should be snug and not fit if folded. .020 is about the spec but not rubbing when off.

It's a common problem but might take a puller to get clutch off??

T
_________________________________________
Long retired now


RangerGuy
User

Jun 13, 2011, 5:44 PM

Post #7 of 23 (3613 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

I checked the air gap using a biz card and it seems to have the proper amount of air gap.

Can you tell me where to locate the TPS? I would like to check or replace that to eliminate it as a possible source of the voltage cut out at the compressor when the clutch is cycling.


Hammer Time
Ultimate Carjunky / Moderator


Jun 13, 2011, 5:49 PM

Post #8 of 23 (3610 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

It's mounted to the side of the throttle body but don't try to change it unless you are equipped and know how to adjust it properly.






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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



RangerGuy
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Jun 13, 2011, 10:02 PM

Post #9 of 23 (3601 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

I took a look at the TPS and it looks like it is the non adjustable type. I changed one a few years ago on another vehicle and it had slots where the screws held it on so you could rotate it and get it set correctly. The one on this old ranger doesn't have slots where the screws attach.

I started the truck up again this afternoon and put the gauges on it again and just observed everything that was going on in case I missed something earlier.

Here is what it did today: Started engine with a/c on max, blower on high and the clutch engaged and it remained engaged for about 6 or 7 minutes. It didn't cycle at all during that time so I thought maybe it mysteriously fixed itself. Then I ran the throttle up to about 1800 rpm. for a minute and when it returned to an idle the a/c compressor cycled fast about 8 times and then it engaged and stayed on for about one minute. Then the whole process of fast cycling started again and every so often it will stay engaged for a minute, maybe two minutes and then cycle fast again 8-12 times or so. As soon as I increase the rpms to about 1000-1200 it will stay engaged.

When the clutch is engaged the low side pressure was 40 and high side was about 205 and it was about 78-80 degrees outside.

Based on what you've heard about this ole truck throughout this post do you think I should put on a new TPS? Or is there something else I could do, check or replace instead?


Hammer Time
Ultimate Carjunky / Moderator


Jun 13, 2011, 10:37 PM

Post #10 of 23 (3594 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

We don't replace parts on guesses like that. We test it to look for a look for a glitch in the signal. If none found, we look elsewhere.




~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



RangerGuy
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Jun 16, 2011, 5:35 PM

Post #11 of 23 (3576 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

TPS had a dead spot on sig wire round 3.3, ref volts and return checked out fine. Installed new TPS and checked before starting engine, has same dead spot at about 3.3. A/C clutch still cycling. Any ideas?


(This post was edited by RangerGuy on Jun 16, 2011, 5:35 PM)


Tom Greenleaf
Ultimate Carjunky / Moderator


Jun 18, 2011, 11:35 AM

Post #12 of 23 (3556 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

Ranger: This thing will cycle dependent on charge and temps. Need pressures at what ambient temp and take center vent temp and we can move on. If cycling and hot out - say 80F or more it really shouldn't cycle at idle but may with some RPMs. It probably just needs a boost but know what you are doing or risk major destruction of the system,

T
_________________________________________
Long retired now


saturn tech
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Jun 19, 2011, 12:15 AM

Post #13 of 23 (3550 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

Check the for a weak fan clutch, the high side pressure may be too high, cycling the compressor off. A peice of cardboard should not be able the stop the fan at idle.


Hammer Time
Ultimate Carjunky / Moderator


Jun 19, 2011, 12:21 AM

Post #14 of 23 (3547 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

That wouldn't seem to jive with his "idle only" problem. He has no problems off idle.




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



RangerGuy
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Jun 19, 2011, 11:22 AM

Post #15 of 23 (3534 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

Ambient temp 90 degrees, low pressure 40, high pressure about 280, center vent temp 65 or lower when engine is running at (1200 rpms) which is when clutch stays engaged normally. Vent temp raises to 80+ when you sit at an idle (800 rpms) b/c compressor is cycling.

Recall from my earlier posts that I have verified I'm losing voltage at compressor when it is cycling at idle 800 rpms.


RangerGuy
User

Jun 19, 2011, 11:29 AM

Post #16 of 23 (3531 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

Anybody have ideas on why the new TPS has the same dead spot as the old TPS?

Thought that was going to to be the source of the problem when I replaced it.

Anybody know know what switch, relay, component, etc. I could check next that could be cutting out the voltage to the compressor at idle?


Hammer Time
Ultimate Carjunky / Moderator


Jun 19, 2011, 11:58 AM

Post #17 of 23 (3527 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

I'm sure you're just testing the TPS wrong but that high side pressure is too high.




~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



saturn tech
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Jun 20, 2011, 3:11 AM

Post #18 of 23 (3518 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

A weak fan clutch off idle will still move enough air through the condenser to prevent the high side switch from disengaging the compressor. At idle without enough air flow the pressure will quickly rise and cause the compressor to cycle on and off exactly as the symptoms describe. I had the exact same vehicle that a couple of other shops could not figure out the problem, I replaced the fan and the problem was fixed. The TPS in this system turns off the compressor at WOT, to cause this at idle it would have to read over 4v. Check the fan as I described earlier.


Hammer Time
Ultimate Carjunky / Moderator


Jun 20, 2011, 6:18 AM

Post #19 of 23 (3514 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

So when the RPMs are increased, the compressor isn't building even more pressure? Any high pressure problem I ever saw got worse when RPMs are increased, regardless of the cause

Yes, the TPS would have to short to full voltage to simulate WOT but that happens all the time. That has been eliminated here.




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



RangerGuy
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Jun 20, 2011, 9:01 PM

Post #20 of 23 (3504 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

Saturn Tech - checked the fan clutch at idle rpms by putting it through the cardboard test and I have stiff piece of rubber so I tried that too and there was no way I could stop the fan, too strong.

Hammertime - Checked the pressures again this afternon - 91 degrees in front of radiator, low pressure 38 high pressure 225, this is at 1200 rpms. when I increase rpms to about 1500 + rpms I watched low pressure slowly drop to near 26 and high side slowly increase to maybe 275, I had to really incease rpms to around 2200-2500 to get the pressure to move this much.

I'm thinking now maybe I have partial blockage in an orifice or expansion valve the way these pressures are moving. Is my thinking right on this? I still have no idea what is causing the voltage to cut out at the compressor at idle rpms.


(This post was edited by RangerGuy on Jun 20, 2011, 9:02 PM)


Hammer Time
Ultimate Carjunky / Moderator


Jun 20, 2011, 9:08 PM

Post #21 of 23 (3496 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

No, your pressures are fine. It's got to be something electrical. You'll have to follow a wiring diagram to see where it's dropping out.








~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



RangerGuy
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Jun 21, 2011, 4:48 PM

Post #22 of 23 (3483 views)
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Hammertime - That diagram is great! I will work on it, it may take me a couple of days but I will work through it and post and update.


Hammer Time
Ultimate Carjunky / Moderator


Jun 21, 2011, 5:44 PM

Post #23 of 23 (3481 views)
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Re: 89 Ranger a/c clutch cycling at idle speed [In reply to] Sign In

Let me know if there is anything you don't understand in the diagram.




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.





89 Ranger a/c clutch cycling at idle speed


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