Hi,new guy here with an AC question.I have a 1996 Yukon that I have had for 2 years and the AC has never worked as long as I have had it.The previous owner said he had it checked and the compressor is bad.I unplugged the harness that connects to the compressor and checked for power.There are 2 wires going into the connector,green and black.I checked both wires with a test light and dont have power on either one.Could this be my problem?
New guy with an AC question
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SunlitComet
OBS Jedi-Do Good
Welcome again is this the connector up top on clutch unit or at the rear of compressor.
If up front lets start out by checking out your compressor relay in the under hood block. If you probe for power in the relay socket you should see bat voltage on two different terminals with ignition on. They are fed by "IGNE" and "A/C comp" fuse if that is fine reinstall relay and listen to see if it clicks with engine running when a helper turns on the a/c from inside. If not ensure the light green wire on back of hvac control head puts out battery voltage when a/c is selected and fan is on. Start with that. Also do you have any info on the refrigerant charge status ?
If up front lets start out by checking out your compressor relay in the under hood block. If you probe for power in the relay socket you should see bat voltage on two different terminals with ignition on. They are fed by "IGNE" and "A/C comp" fuse if that is fine reinstall relay and listen to see if it clicks with engine running when a helper turns on the a/c from inside. If not ensure the light green wire on back of hvac control head puts out battery voltage when a/c is selected and fan is on. Start with that. Also do you have any info on the refrigerant charge status ?
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Thanks for the reply.This is the connector on top right behind the pulley.I dont see another connector on the compressor.I pulled the relay and I do have voltage on two terminals with the ignition on.I dont have anybody here to help check the relay right now so I just swapped it with the starter relay since they are the same and still nothing.I dont have the dash apart so I cant check the control head but I do have voltage at the dryer so I guess that means I have voltage coming from the control head.I'm just wondering if the problem is in the wiring and not the compressor since I dont have voltage at the compressor.
As far as the refrigerant goes,I have no idea.
As far as the refrigerant goes,I have no idea.
SunlitComet
OBS Jedi-Do Good
The various pressure switches will have voltage present on one side and the engine computer reads them by which ones are on or off to see if it is safe to operate the compressor. As for the other connector on the compressor you should see a red colored connector or body out the back but reccessed in the unit. It shoul have two wires on it too. That it the high pressure "I am about to blow up" cut-off switch. should also see one on top of the compressor line block colored green or black and again on the drier/accumulator unit. With engine off can you turn the compressor by hand from the front? Also keep in mind if engine is not actually running the compressor is disabled. The computer has final say on weather or not compressor relay is activated. Any chance you can get a freon refill kit with a gauge? After all these years of not running I am sure it will need it. There is a possibility that after such a long time not operating the compressor may have or will develop other problems. Typically one of the first hings you check when non-operational is a low freon charge.
OK,I found the other connector on the back of the compressor.Dont know how I missed that,it was right there in front of me.I am getting voltage there so the only connector that's not getting voltage is the one on the front just behind the pulley.And I can turn the compressor by hand when the engine is off.
SunlitComet
OBS Jedi-Do Good
That is about right your computer may not be activating the clutch relay becuase the freon charge may be way to low. A gauge set or refill kit with gauge would really be good right now if you can get it.
SunlitComet
OBS Jedi-Do Good
No unless you have a jammed, damaged or worn out compressor it does not need to be replaced. If you are convinced you have a decent charge in it then something electrical is getting in way. When can you pull off your dash bezel to check hvac head unit. Does it a/c indicator bulb light when that and fan is turned on?
It will be the weekend before I can take the dash bezel off.When I turn the AC on the button does light up.I cant say for sure that I have a full charge but when I hook the guage up it is showing full.I am not an AC guy so this stuff is alien to me.I can change the parts out no problem,but I dont have any experience diagnosing the AC system.
This is totally unrelated but the funny thing is I bought this truck 2 years ago and I have not spoken with the previous owner since then because we live about 30 miles apart and we dont know each other except for the transaction with the Yukon.He emailed me this past Saturday night and asked if I would sell it back to him because it was his dad's before he got it and it has a lot of sentimental value to him.
This is totally unrelated but the funny thing is I bought this truck 2 years ago and I have not spoken with the previous owner since then because we live about 30 miles apart and we dont know each other except for the transaction with the Yukon.He emailed me this past Saturday night and asked if I would sell it back to him because it was his dad's before he got it and it has a lot of sentimental value to him.
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SunlitComet
OBS Jedi-Do Good
if the light comes on lets assume that the head unit is fully functional. Take the connector off of each of the pressure switches and jumper them with the a/c on and see if one activates the system. Do not let it run beyond 5 seconds at first and gradually increase each time to see if if the aluminum lines on the compressor get hot and cold separately. any mechanical noises that get out of hand shut it down, if one line gets burning hot in a few seconds shut it down, If it stalls your engine-well it will shut itself off if there is not change in temperature on the lines shut it down. Once you seem comfortable that it is cycling on and of about 8 times a minute see how the air inside feels. Report back with results.
SunlitComet
OBS Jedi-Do Good
No just disconnect one sensor connector at a time and jumper the two wires in them. while the other connectors are still attached.
99whitehoe
TYF Newbie
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Like was already said sounds to me like your low pressure switch is open causing you to get no voltage to the compressor switch located behind the compressor clutch. Just because you have pressure on your gauge does not mean that your system is full of refrigerant. If you jump out your low pressure switch and the compressor comes on I wonder what your pressure would be. I would think that if your compressor still does not come on once you jump the low pressure switch then your compressor clutch or compressor itself is locked up. Just my .02
Thanks alot for all the advice.It looks like I'm getting somewhere now.When I put the jumper in the connector on the dryer the compressor kicks in with no funny noises.I let it cycle on and off about ten times and then put a can of freon in while I left it running.The line going straight back towards the firewall gets a little cooler and I think I was getting a little cooler air in the truck.I guess if I get more freon I will be in business.
SunlitComet
OBS Jedi-Do Good
that is supposed to be the cycling switch. After you fed some refrigerant into it were you able to reconnect it and it would would on it own? remember only to open the freon valve when compressor is engaged so the freon does not have to fight so much to get in the system. just don't over charge.
---------- Post added at 10:30 PM ---------- Previous post was at 10:29 PM ----------
One other thing if you get more refrigerant get some with a UV dye in it so you can get a UV light and find leaks in the darkness.
---------- Post added at 10:30 PM ---------- Previous post was at 10:29 PM ----------
One other thing if you get more refrigerant get some with a UV dye in it so you can get a UV light and find leaks in the darkness.
OK,I added another can of refrigerant with dye today and the air blows pretty cool now.I dont know how accurate my guage is since its the cheapy that comes with the refrigerant from Walmart but when the compressor first kicks in it shows 35 psi and after running for about 10-15 seconds it drops to 25 psi and the compressor turns off.It stays off for about 5-10 seconds and comes back on.Does this sound right?I dont know how much refrigerant is needed but I have put about 27 ounces in so far.
Once again,thanks for all the help.The dealership quoted the previous owner $1000 to repair it and thanks to you guys I have less than $35 in it.
Once again,thanks for all the help.The dealership quoted the previous owner $1000 to repair it and thanks to you guys I have less than $35 in it.
Yes you need more. The switch trips at about ~23 psi. If it is tripping at idle, then you need more freon because as soon as you drive/rev the low side will go even lower. You may be 1-2 full cans low still. Make sure you are doing this with the blowers on high.....that is important, otherwise the evap gets so cold the pressure drops and it cycles.
A normal system will cycle at idle if the blower is only on low.
A normal system will cycle at idle if the blower is only on low.
SunlitComet
OBS Jedi-Do Good
see if you can bump it up another 5 psi on the first number to ballpark it and be absolutely sure you valve cap is clean inside with no damage inside either and do not over-tighten it. Call your self good for now and keep an eye out for leaks. Always run your compressor for a about 10 minutes each week to keep the system in good shape.
---------- Post added at 06:47 PM ---------- Previous post was at 06:36 PM ----------
BTW your cycling rate is in a good area as well.
---------- Post added at 06:47 PM ---------- Previous post was at 06:47 PM ----------
you should get about 8 a minute while idling.
---------- Post added at 06:51 PM ---------- Previous post was at 06:47 PM ----------
If you are not cycling about that much when idling you charge may be getting low. If it stays on continuously not matter how hot it is, that will be the sign that it is time to go back in and find the leak
---------- Post added at 06:55 PM ---------- Previous post was at 06:51 PM ----------
Nuetral or drive running should not be an issue the rpm is bumped as needed by the PCM to always maintain a required 650 rpm minimum. Steering load, in gear, A/c on, lights doesn't matter.
---------- Post added at 06:47 PM ---------- Previous post was at 06:36 PM ----------
BTW your cycling rate is in a good area as well.
---------- Post added at 06:47 PM ---------- Previous post was at 06:47 PM ----------
you should get about 8 a minute while idling.
---------- Post added at 06:51 PM ---------- Previous post was at 06:47 PM ----------
If you are not cycling about that much when idling you charge may be getting low. If it stays on continuously not matter how hot it is, that will be the sign that it is time to go back in and find the leak
---------- Post added at 06:55 PM ---------- Previous post was at 06:51 PM ----------
Nuetral or drive running should not be an issue the rpm is bumped as needed by the PCM to always maintain a required 650 rpm minimum. Steering load, in gear, A/c on, lights doesn't matter.
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I think you have that part backwards.
At idle if it is hot out and the system is charged correctly and on high blower.....it will never cycle. At idle the low side will be around ~32-45 psi depending on the ambient and in-truck ambient.
If you put the blower on low, then when the evap gets cold enough, the pressure will drop to 23 and it will start cycling.
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