[FIXED] 08 suburban will not take Freon from low side

Hi new to the site….I have a 08 suburban with a 5.3 and I replaced the ac. Compressor,accumulator and orffice tube….I vacuumed the system down for 40 min than let it sit for 3 hrs with no leaks present and when I hook my gauges up and open the low side port nothing happens and the ac light blinks on and off….I did use the danner method and pressured the system with air to see if everything worked like it should and it did….the light had stopped blinking and compressor came on…I ran it for 5 seconds and turned it off….yet when I vacuum the system it will not take anything….now if I open the high side it will take a few ounces but then the compressor will just run on and off for like 2 seconds continuously…and the ac light still blinks 3 times….I tried to jump the low side switch and nothing the compressor will not engage….I’m assuming the light is blinking cause it has no pressure in it but it will not take any Freon from the low side at all! Please can someone help me with this…I will mention I’m a diesel mechanic for 20 years now so I’m not a rookie lol but I’m not to familiar with these new computer cars….any help would be appreciated 

Unfortunately, on this system, jumping the low side switch isn't enough. There's the A/C Pressure Sensor on the discharge line which reads actual system pressure. Like you guessed, it's probably reporting low system pressure to the PCM.

It may be that you're setting a current code for the A/C Pressure Sensor in the PCM by having the engine running with the system under vacuum. :huh: If you have a scan tool available, you could confirm that pretty easily. Would it be possible to charge the system with a pound or so, then clear codes and start the engine? That'd allow the sensor to have a rational reading, and get the compressor to short cycle long enough to get the rest of the charge in.

Your other option would be to jump the compressor. Here's a diagram for reference:

 

You can jump the relay if you're comfortable? But I'd suggest jumping 12V to fuse #17 A/C CMPRSR instead. Less chance of inadvertent damage.

Unfortunately my autel is at home 3 hrs away I had came up here to help my grandad out by replacing his compressor so no I don’t have access to one…I think he does have a cheap code reader that I will hook up when I get back to working on it in few hrs…but I would figure after a good vacuum that with engine off it should still take some Freon until the pressures equals out but this thing won’t take any of the can ….it will when I open the high side but then it acts like something is wrong cause the compressor just kicks on and off really fast….I never seen a vehicle that wouldn’t take and Freon after a vacuum

I’m not to good at wiring like danner said if you not to familiar with it you can cook a computer….but if I tried would I jump pins 30 and 87 to make the compressor come on?

wrote:

…but I would figure after a good vacuum that with engine off it should still take some Freon until the pressures equals out but this thing won’t take any of the can ….it will when I open the high side but then it acts like something is wrong cause the compressor just kicks on and off really fast….I never seen a vehicle that wouldn’t take and Freon after a vacuum

I agree. I've done many full charges on these vehicles with the engine off. Are you sure there weren't packaging plugs in the new accumulator that would prevent flow? Does the low side port (on the accumulator) actually open like it should?

You can definitely jump the relay pins. But, since the A/C CMPRSR fuse is after the relay, you can jump power to the fuse directly and not have to worry about making sure you're on the right relay pins. Zero chance of letting the magic smoke out of the PCM that way.

Well since I pressured the system with air it worked great so that should also rule out any plastic caps…it just for some reason will not take any Freon

Update it ended being my cheap gauge set….i was confused that the compressed air went in with no problem….but I got to thinking maybe the forced air forced its way in the valve and the single can didn’t have enough pressure to force its way in? idk but all I did was reach down and twist the low side valve down more …I had to twist it pretty hard so I will be getting a new set of gauges! But thanks to all the fast response very much appreciated

Glad to hear it!

I was about to suggest that the low side valve was somehow not getting opened, but you're way ahead of me. So you probably didn't need to short the compressor once you got the low side to accept a charge?

Nope didn’t have to …once it sucked in that one can I cranked it up and the compressor came on and took in the other 2 cans