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1998 gmc suburban ac does not work
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jhoney
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May 22, 2010, 7:23 PM
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1998 gmc suburban ac does not work
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i am trying to fix the air conditioning on my sister in laws suburban. i am not the greatest when it comes to the electrical part of things but try. i have tested and i am getting power to the back of the compressor. i can turn the switch off inside the car and it turns the power off at the back of the compressor. i have ran power from the battery to the clutch fan and the clutch will engage. i am not showing any power to the clutch fan, high side or the low side pressure switch. i have wondered about the switch being bad but like i said i am not that great at this area. any help would be appreciated
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Hammer Time
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May 22, 2010, 7:33 PM
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Re: 1998 gmc suburban ac does not work
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What do you mean by power to the back of the compressor? Are you getting power and ground to the clutch plug?
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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.
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jhoney
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May 22, 2010, 8:22 PM
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there is a plug in the back of the compressor that i am getting power at and then there is a plug for the clutch. i am not getting any power but it is showing ground at the plug for the clutch. i can jump the power from the battery to the plug for the clutch and the clutch will engage.
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Hammer Time
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May 22, 2010, 8:26 PM
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That's your high pressure switch. You can try jumping that switch out to test that but it's not wired directly to the compressor. It just signals the PCM. Check your fuses too. I assume you have checked the refrigerant pressures to make sure it has enough refrigerant to engage.
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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.
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jhoney
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May 22, 2010, 8:30 PM
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yea i have checked all fuses and switched out the relay. the high pressure switch is on the top of the compressor mounted on the line set. there is another plug on the compressor itself mounted on the back side at the bottom of the compressor. it gets power when you turn the switch on and turns the power off by turning the switch off
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Sidom
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May 22, 2010, 9:38 PM
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The best place to start on this would be the clutch relay. There's 4 circuits and 3 can be checked quickly. 2 are just power sources and both (#30 & #85) should have 12v with the key on. #87 is the feed for the clutch, if you run a fused 12v jumper to this terminal, the clutch should engage and tell you that circuit is good (which explains the ground on the clutch connector). #86 is the term the PCM grounds to turn the system on....
You've already jumped all 3 pressure connectors, so if one was bad the a/c would've come on. Check the easy 3 terms of the relay I pointed out (if you decide to run a fused jumper to #87 to engage the clutch....MAKE TRIPLE SURE YOU AREN'T JUMPING #86 & SENDING 12V TO THE PCM...... I need to say that again.....MAKE TRIPLE SURE YOU AREN'T JUMPING #86 & SENDING 12V TO THE PCM)
If those 3 circuits check out then for some reason the PCM isn't grounding the a/c clutch relay..... With a scanner it's pretty easy to track down but there is a bunch of reasons why the PCM won't turn on the a/c so if you don't have a scanner it might be a good idea to have it check out.......
Whoops almost forgot.....whatever you do......MAKE TRIPLE SURE YOU AREN'T JUMPING #86 & SENDING 12V TO THE PCM......That would be a very very expensive mistake...... and don't use a test light on the pressure sensor connectors wires either, those are also comp signal lines.....
There should be a diagram on the relay......The clutch will be 87.......On the control side #85 is usually the power source & #86 the ground for the PCM..... Some times they will reverse it & 86 will be power & 85 ground, which everone has power the ground will be the other one...........The load circuit (in this case the clutch) is always #87
If you want to test #86, get a digital voltmeter & hook the pos to batt + and the neg to term 86, turn the a/c on and you should se batt voltage, if not the PCM isn't grounding the relay for whatever reason and that is the circuit with the problem......
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jhoney
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May 25, 2010, 6:06 PM
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Hello Sidom,
I have done what you said to do. I found out i am not getting a ground to#85 and no power to #30. i jumped a power wire to #30 and aground to number #85 and it all works. I was wondering if you could tell me where the power for #30 is suppost to come from so i can check it at that point. the wire for #30 is a green with white stripe. there is the same color wire running out of the back of the compressor but when checking to see if there the same wire i am not getting anything. I guess the wire could be broke but just wanted to see if you know where #30 runs from to the relay. Thanks for your help
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Hammer Time
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May 25, 2010, 6:31 PM
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That is powered by the "ignition E" fuse (10A), powered only when the key is on. The PCM ground will only apply when the computer is satisfied with all the inputs that it monitors so there can be many reasons that you, correctly, don't have a ground there. Most commonly, it's a switch that does that. You can jump out the switch plugs to test them.
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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.
(This post was edited by Hammer Time on May 25, 2010, 6:31 PM)
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Tom Greenleaf
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May 26, 2010, 6:40 AM
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Sorry if I missed it - but back some you were asked by HT if pressure (static) was enough. Is it? Should be close in PSI as the temp in Fahrenheit with it just sitting there. If not, there's no point in chasing anything else as it would be disabled by low pressure switch,
T
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jhoney
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May 26, 2010, 8:16 PM
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ok tonight i swapped out the controls with another set out of a friends truck. it did not change anything. I put my guages on the ac and it reads it is full 40psi. I was wondering if the high or low pressure switch would kill the power to the one prong on the relay? I am going to buy a different manual and see what it shows in there for the wiring diagram and see if i can trace down where the power is suppost to come from.
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Sidom
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May 26, 2010, 8:58 PM
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I just reread this thread and noticed there is a lot of the same advise being offered here and I'm not sure if it's being followed.
1st is pressure.... Is there enough to start the system????? 40 psi.... That's low.... Jump the low pres c/o switch on the accumulator with whatever.... wire, paperclip, cotter pin, old lady's bobby pin..... If it doesn't come on then jump the switch at the back of the compressor. If it comes on, evac the system & change the sensor.... The just to be safe jump the h/p switch on the liquid line....
My post was assuming all this had been checked and confirmed. I'm not gonna type all that again....... confirm 2 power sources at the relay KOEO (if not.....fix it before moving on), confirm the clutch engages when the load circuit is energized...All the checks out now it's time to find out why the PCM isn't grounding the relay
Next step would be to grab the scanner & check PCM, BCM & HVAC for stored coded.. None found, manually start going thru ALL the PIDs the will make the PCM deny a/c when requested. temp sensors, tps, charging PIDS, It's late & I know I'm forgetting a bunch.... Swaptronics like you'e starting to try does work, on some problems.....On this problem.....it can be a very very long road...... My advise once again.....If it comes done to a PCM problem.......without a scanner.....it might be best to take it in......
Good luck with the decision you choose.........
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jhoney
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May 26, 2010, 9:09 PM
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i want to say thanks for everyone who has posted. i am going to have him take it to the shop and have them check the freon in it. my gauges shows it right at the warning level. i do not have much experience in this department at all. i will post and let everyone know what the out come is. I was just trying to help them out to save them money but i think it is time to let the pros handle it.
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Tom Greenleaf
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May 27, 2010, 1:34 AM
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">>I put my guages on the ac and it reads it is full 40psi.<<"
(note: gauge doesn't know it's full it's just a pressure. Any gauge that says full on it should go back to toy land and yes they make them - they are called Death Kits!)
40 psi suggests engine area temps were about 45 degrees Fahrenheit. If engine had been run it would be warmer underhood than that on a colder day.
If that reading is accurate there's no point in fussing with electrical anything right now as it's near empty! Act quick to find and fix the leak. If you really saw that # depending on speed of the leakdown and where system could have sucked in air on low side while still having enough pressure to engage and the low reading would go into vacuum sucking in air messing up all readings. Low pressure cut out switch will not allow compressor to stay engaged at about 26-30ish and may not re-engage till it sees 40 PSI or a tad more.
Right now unless I missed something this system is in shutdown mode by pressure alone. Problem is if air is now in there and has been for a while the oil used goes acidic and becomes a problem. Hard to know exactly. At that low # I would look for oily evidence for the leak at shaft seal, compressor body, service ports, any connections, condenser, evaporator drain for oil or anywhere refrigerant could be.
All the switching is mostly safeguarding system and preventing ice. High side will cut off system if too high to prevent damage hopefully if so. Back of compressor may or may not have a thermal switch which will also disable system if too hot.
So far for the era all these switches are sensing pressure or one may sense temperature. They don't know if the pressure is air, refrigerant or what.
If you find an oily area you can sniff it out with an electronic detector to help verify. Evacuate system to hold a vacuum for at least 1/2 hour to see if it will hold. If not there's still a leak.
In that perhaps 2/3rds to 3/4ers of all A/C problems stem from leaks that where you should be looking first. If then known sealed tight with known charge properly and it doesn't work you move on from there.
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Hammer Time
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May 27, 2010, 2:46 AM
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40 PSI is marginal on a running compressor. It's certainly not enough static pressure to engage the compressor. The system is out of refrigerant.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.
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jhoney
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May 27, 2010, 5:25 AM
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thanks guys yea the gauges i have are not anything special at all. they are just some cheap ones i had purchased to be able to add freon to my moms car some time back. they are color coded green,yellow and red. i am having him take it to a shop and have them vacuum it down and and check it all for leaks. i know last yr he had a small shop replace the line set and the condensor and it only worked a few weeks before stopping again. his wife is on him to get it fixxed this yr. thanks for eveyones help.
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jhoney
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Jun 10, 2010, 8:44 PM
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ok it is fixxed now. turn to find out it was the connectors them selfs that were causing the problem. when checking it with the tools i have it showed everything to be working but when connected they were spread to far apart to make connections. one was at the relay and one was on the low pressure switch. we also had it vacuum down and filled with freon and some oil. thanks for everyones help.
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Sidom
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Jun 10, 2010, 8:51 PM
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Glad to hear you got it going.....Thx for letting us know what fixed it........
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