AC not working

Tiny
CZR1760
  • MEMBER
  • 2004 CHEVROLET IMPALA
  • 202,000 MILES
This started with the fact that my wife's AC was not blowing cold air. I hooked manifild gauges and found that both high and low side pressures were low, making me think that it was low on coolant. I added leak detector dye to the system and by the time I was going to add refrigerant, the coolant was boiling back up into the resevoir. I immediately shut down the car. No coolant in the oil, no wetness on passenger side floor. After checking the thermostat (195), it did not open until after water rapidly boiling (and opened barely). I flushed the system, installed a new cap and thermostat (180). Now I filled the system and got it up to temp, and noticed that the cooling fans did not come on at all. Would not turn on with AC on or heater. All fuses checked out OK, but did not test relays, as it was getting dark. I also noticed that while on heat, the driver's side air was not very hot, neither side was cold on AC. I have also (within the last sevearl months) replaced the coolant temp sensor and rear O2 sensor, trying to get rid of engine light code (to no avail) have not had it scanned recently. I know that this is a lot of information and I'm not sure if they are all related or not, but wanted to give everything. Please help, this thing is driving me crazy.
Wednesday, July 11th, 2012 AT 1:18 AM

48 Replies

Tiny
DJCL
  • MECHANIC
  • 767 POSTS
First check the under hood junction block fuses. 2 - 25a fuses fan control one and fan control 2&3. See if there is voltage on the lt blue wire and the grey @ the 2 fan motors. Try adding power on them and see if they run verify good grounds on the one black wire. If you can get a scanner it would help a lot we will want to check to see if there is a ac request and fan command. Than try to run the fans with the out put command. @ The ecm in the air cleaner key on try to ground the dark blue and dark green @ pins 5 and 6. This will run the fans low and ho speed.
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Wednesday, July 11th, 2012 AT 1:36 AM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
So when you turn the ac on does the ac clutch kick in and the compressor start spining in the center of the ac clutch?Have you checked the cooling fan fuses yet?Also were the fans on when the coolant was boiling over?Do you know what temp it was boiling over at?
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Wednesday, July 11th, 2012 AT 1:39 AM
Tiny
CZR1760
  • MEMBER
  • 49 POSTS
I will put a meter on it tomorrow and verify power. I did test fuses, everything was good. Did not test relays. I don't have access to a good scanner, jsut test light and voltmeter. As for the compressor, it does kick on and spins (not forzen up), but still no fan. I could not say for sure that the fans came on last night or not. The dash board temp gauge was reading over half, I would estimate 220-230, which is high for this car (usually doesn't get half way). I almost forgot. About a month ago the car overheated due to loosing coolant, I ended up renting a hauler and towing it home. I tried to limp it, but it was not gonna happen, coolant was everywhere. One of the plastic elbows rotted away by the water pump and needed replaced. I replaced both elbows, refilled and burped the system. AC worked at that time.
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Wednesday, July 11th, 2012 AT 1:52 AM
Tiny
DJCL
  • MECHANIC
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The a/c compressor will be shut down by the ECM if the engine temp is to hi
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Wednesday, July 11th, 2012 AT 1:58 AM
Tiny
CZR1760
  • MEMBER
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Ok, here is what I have found out so far. Both fans will power on when jumped directy to the battery. Both fans will come on if the tempature control sensor. I do not show any volts at the white wire or light blue wire, at fan plug ends. Key off, I have power on #85 for all three relays & #30 on relays, 1 & 3, 13 volts. Car running power on #85 & #30 on all three relays, 14 volts. Power on #87 on 2 & 3 & #87a, 17 volts. Also found. Key off, IF apply test light to #86 on #1 relay both fans come on low. IF apply test light to #86 on #3 relay pass side fan comes on. Clicking sounds when using test light to said leads. Burned my fingers trying to test #2 relay, nothing to report.
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Wednesday, July 11th, 2012 AT 10:45 PM
Tiny
CZR1760
  • MEMBER
  • 49 POSTS
When you speak of the BCM, I'm wondering if this may be the root of the problem, although I'm not ready to run out and buy one (ouch pricey). I know that intermitantley, the security light will come on and then the car will not start. Wait a while and bingo, it starts. I've been told that the BCM controls the pass lock as well. Maybe I'm over thinking, but just asking. I've also been told how to bypass the pass lock and just haven't done it yet.
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Wednesday, July 11th, 2012 AT 10:52 PM
Tiny
CZR1760
  • MEMBER
  • 49 POSTS
Tried to make sure that I had no air in the system, so I ran the car up to temp. Neither fan came on, coolant bubbling back out of filler neck so I decided to shut off car. Bad idea. Coolant launched out of filler neck. After refilling and replacing cap I started the car and hosed off engine and got a quick whine noise (like a belt whine, but deeper tone), but went away quickly. As car ran, temp got to almost half way, no fans and coolant started boiling back into resevior and more whining this time. Whinig continued after shutting the car off. I could not identify if the whine was coming from boiling coolant of possibly something else. I hope this helps diagnose the problem and just doesn't add more confusion to an otherwise frustrating problem. Thanks.
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Wednesday, July 11th, 2012 AT 11:52 PM
Tiny
DJCL
  • MECHANIC
  • 767 POSTS
Its looking like the ecm is not grounding the relays. We will need a scaner to go deaped in to it.
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Thursday, July 12th, 2012 AT 12:11 AM
Tiny
CZR1760
  • MEMBER
  • 49 POSTS
Ok, but I don't have access to a scanner anymore. Is there anyway to diagnose this porblem without the use of a scanner? I know that if I go to Auto Zone, they will just use a low end scanner that will not be albe to make any commands. Is this (ECM)an explination for the coolant backing up into the resevior?
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Thursday, July 12th, 2012 AT 12:23 AM
Tiny
DJCL
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If the fans don't turn on and the engine temp is gettint hot the coolant will back up. The pcm turns on low speed @ 217 f and hi speed @230 f
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Thursday, July 12th, 2012 AT 12:35 AM
Tiny
CZR1760
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  • 49 POSTS
You mentioned an ECM first and then a PCM, are you speaking of these interchangeably?
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Thursday, July 12th, 2012 AT 12:40 AM
Tiny
DJCL
  • MECHANIC
  • 767 POSTS
Same thing. Its mounted in the air cleaner box
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Thursday, July 12th, 2012 AT 12:43 AM
Tiny
CZR1760
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  • 49 POSTS
In quick research, this isn't something that I can quick swap out, dur to needed programmed at the dealer. Before I run out and drop some serious cash, do I have any other options.
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Thursday, July 12th, 2012 AT 12:47 AM
Tiny
SATURNTECH9
  • MECHANIC
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Just to add this one a pcm and ecm isnt the same thing a ecm is a engine control module that runs the engine.A pcm is a powertrain control module which is a ecm and a tcm/transmission control module which control the transmission housed in the same box. If there seperate units there labeled as a ecm and tcm together there called a pcm. Also before you start replacing or thinking about replacing a computer I would be looking at the actual coolant temp with a scan tool to see if the sensor reads within 10 degrees of actual coolant temp. Best way to measure coolant temp safely is use a infared temp gun. Amazon sells obd2 scan tools that can read some live data for a little over 50. As far as the cooling fan not coming on with the ac with the pressure readings you had I wouldnt be suprised if it didnt. Could just be a matter of a bad coolant temp sensor or the wiring to it. Unless I missed the part of even checking the temp sensor or what the computer is even reading compared to actual coolant temp?
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Thursday, July 12th, 2012 AT 1:22 AM
Tiny
BRAVESTAR1
  • MECHANIC
  • 234 POSTS
Hi, I just did all this same work on my Car. It's 98 Sable, but I can tell you from experience, given I've also got one of those, that your water pump is probably broken. If it's not circulating the water, then the thermostat won't do squat. Thus your car will over heat, and kaboom!

Also check the ECT Temperature Sender. Its the one that looks like an old style Propane tank connection, not the cylinder one. Careful taking it off, as it might be brittle. This is likely why the fans won't come on.

Lastly take your car to a Valvoline or Jiffy Lube, and have them pressure test the vacuum to see if there is any leaks. For me the cause was over time, the R-134 leaks through the hoses, the system held vacuum for 20 mins, and pressure for 30, so the "free test" was worth it. Then they put in the proper coolant and oil, and the cold air made the $143 worth it.

See this question for additional details with pictures. https://www.2carpros.com/questions/2000-mercury-sable-fuse-located-fan-on
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Thursday, July 12th, 2012 AT 1:54 AM
Tiny
CZR1760
  • MEMBER
  • 49 POSTS
Any suggestions as to a resonable priced scanner that is going to help out in this situation? Obviously something that can read live data, but do I also need something that can actually make commands? My friend who used to be a mechanic had a very high end unit, but it was worth more than the car.
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Thursday, July 12th, 2012 AT 2:11 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
A scan tool that will command the fans the only one that I know of is the tech2 which is what the gm dealers use. There is probably another one out there but it wouldnt be cheap.I worked for the gm dealers for many years and used whats called the pdt/portable diagnostic tool then we switched to the tech2 which replaced it. So iam not familar with the advanced scanners the independant shops would use. But they would be expensive lets start with what the coolant temp sensor is reading. Then we can see if its correct and then see if the computer is triggering the relay for the fans. You will also need a infared temp gun to measure engine temp right on the nipple where the upper radiator hose onto the head.I recommend a raytec one I have had mine for over 15yrs never let me down. Heres is a link to the scanner that reads some live data I was talking about.
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Thursday, July 12th, 2012 AT 4:26 PM
Tiny
CZR1760
  • MEMBER
  • 49 POSTS
Working on so many other projects, but wanted to give an update on this one. Never got a scanner, cause I got ripped off on ebay. Anyway, I tried to add some freon and bingo. The fans work. The air coming out of the vents is definetly cool, but not freezing. The passanger side is colder than the drivers side. Now I am hearing what sounds like water or fluid sloshing behind the dash. Could this be the heater core partially plugged? No wettness on the floor or smell of antifreeze.
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Saturday, July 28th, 2012 AT 3:55 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
The sloshing in the dash is probably water trapped in the ac box from a clogged ac drain. You will find the ac drain about the center of the firewall about half way down it will be just a hole or a rubber rubber tube. Clear it and water should come out. The reason the ac probably isnt super cold is because you have the incorrect amount of charge or the pressures are incorrect for other reasons. As far as ebay contact the ebay protection services as long as it hasnt been too long they will take care of you.I had to use them once before they were great. Also isnt your car overheating?
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Saturday, July 28th, 2012 AT 4:54 PM
Tiny
CZR1760
  • MEMBER
  • 49 POSTS
I will try and remove the plug and let you know if water comes out. The readings on the gauges were perfect both hi and low. I didn't want to overfill the system and now I dont' remember the readings, but I know they were good. Car was overheating, but neither fan was coming on. After I added a small amount of freon, they kicked on and the car hasn't been over heating anymore. I'm getting a reading of about 62-64 out of the vent air temp 85-90 outside. Like I said, cool not freezing, but everything seems to be working now. I'm going to check the coolant level too. I've read that low coolant will make a sloshing sounds.
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Saturday, July 28th, 2012 AT 5:06 PM

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