AC Compressor Not Pulling Freon

[Gregski]

Please help I am at my wits end. I have a four door 97 Tahoe with only AC in the front. It was blowing warm air so I "evacuated" the system and then put a vacuum on it with an actual vacuum pump (instead of using an air compressor and that red mickey mouse vacuum conversion pump thingie like I tried before) vacuumed it for 25 minutes then shut off the valves and let it sit there for 30 minutes. It sat and held the 40 PSI vacuum just fine.

FIRST ATTEMPT - Plan A
Then I connected a 14 oz can of freon to the middle hose and expected it to get sucked in without even turning the car on, but it sucked a bit in then I had to start the car and blast the AC and the clutch would not spin.

SECOND ATTEMPT - Plan B
So I disconnected the gauges and connected the can with one of those quick charge blue hoses with a dial on them directly to the low side service port and ran the engine and after what seemed like for ever finally the clutch started engaging for about 5 seconds then shutting off and cycling off and on like that, but still not pulling any freon.

Just so you know I have charged this car and others like this in the past, well... before that stupid blue base cap came out that they make you put on the cans now first before connecting the charge hose to them. And yes I do have the blue base cap and I am using it, but something just aint right.

Please help.

 

[gpracer1]

Did it have freon in it originally?
Did it just stop blowing cold suddenly?

With the gauges on, at what psi does the compressor kick off, and back on. Sounds like possible ac cycle switch.

 

[Phone Man]

I had to jump the pins on the low pressure switch which is the plug on the Accumulator. This will engage the compressor and allow the freon to enter the system. Also you may need to add some PAG oil? I replaced my whole system and had to do that.

 

[Gregski]

Did it have freon in it originally?

Yes

Did it just stop blowing cold suddenly?

No over a couple years the air got warmer and warmer. Till I finally got motivated to do something about it.

With the gauges on, at what psi does the compressor kick off, and back on.

25 PSI both High and Low sides

Sounds like possible ac cycle switch.

Does that bad boy have a shrader valve behind it so I can remove it and not lose any freaon that did go in and have to vacuum the system AGAIN

---------- Post added at 02:45 PM ---------- Previous post was at 02:42 PM ----------

I had to jump the pins on the low pressure switch which is the plug on the Accumulator.

Thank you I tried that with a paperclip.

Also you may need to add some PAG oil?

One of the 14 oz cans I bought claimed to have had the oil in it

 

[gpracer1]

Yes the switch has a valve behind it.

Try turning the can upside down on the first one or two. That should help it cycle less.

 

[JenneK]

Wait...wait... marc, where is this "AC cycle switch you speak of??

I was informed that our trucks have a low pressure (on accumulator) and a high pressure switch (on compressor) with the actual cycling being controlled by the PCM.

My brand new compressor runs all the time EVEN WITHOUT the AC on! I had to rig up a switch so that I could cycle the compressor manually. It works but it's kinda a PITA.

______________

Gregski, you may need to change the orifice tube/expansion valve. Maybe yours is mucked up after no use for so long.

 

[gpracer1]

Wait...wait... marc, where is this "AC cycle switch you speak of??

I was informed that our trucks have a low pressure (on accumulator) and a high pressure switch (on compressor) with the actual cycling being controlled by the PCM.

My brand new compressor runs all the time EVEN WITHOUT the AC on! I had to rig up a switch so that I could cycle the compressor manually. It works but it's kinda a PITA.

______________

Gregski, you may need to change the orifice tube/expansion valve. Maybe yours is mucked up after no use for so long.

The ac low pressure switch controls how cold the evaporator can get. It usually shuts off at 25-28 psi to protect the evap from freezing up in humid environments. For this reason your ac will never blow under about 34 degrees. I installed an adjustable one in mine since I live in a dry area and have it adjusted to blow down to 23-24 degree air.
If you look at a 134a pressure/temp chart you will see, they are directly related.

 

[Gregski]

Well I bit the bullet and bought a brand new $200 dollar compressor and installed it (yes did the PAG oil thing, and new O-ring gaskets for the hose manifold, etc). Vacuumed the system and let it sit for about 45 minutes and it held the vacuum perfect. Then I hooked up a 14 oz can to the yellow hose on my gauge set and opened the valve and it sucked a lot of content into the system, but when I turned on the car the compressor would still not engage, so I shorted the cycling switch plug by the accumulator (silver coffee can looking thing on the firewall) and the clutch engaged but it still would not suck more freon in, then I plugged the low pressure switch back in and the clutch now engages for 5 seconds just like it did with the old compressor and then disengages, then it repeats that for eternity

well at this point I don't know any more, what does it mean when the 14 oz can feels cold and has condensation no it, does that mean it is pulling freon out of it? and it's just going to take for ever, shouldn't it be done in 10 minutes or so?

Shouldn't the low pressure hose muffler get cold to the touch, it is not?

Could it be the pressure switch in the high pressure hose line, is it not opening some valve which would allow the system to suck in more freon?

 

[letsbangout]

Well I bit the bullet and bought a brand new $200 dollar compressor and installed it (yes did the PAG oil thing, and new O-ring gaskets for the hose manifold, etc). Vacuumed the system and let it sit for about 45 minutes and it held the vacuum perfect. Then I hooked up a 14 oz can to the yellow hose on my gauge set and opened the valve and it sucked a lot of content into the system, but when I turned on the car the compressor would still not engage, so I shorted the cycling switch plug by the accumulator (silver coffee can looking thing on the firewall) and the clutch engaged but it still would not suck more freon in, then I plugged the low pressure switch back in and the clutch now engages for 5 seconds just like it did with the old compressor and then disengages, then it repeats that for eternity

well at this point I don't know any more, what does it mean when the 14 oz can feels cold and has condensation no it, does that mean it is pulling freon out of it? and it's just going to take for ever, shouldn't it be done in 10 minutes or so?

Shouldn't the low pressure hose muffler get cold to the touch, it is not?

Could it be the pressure switch in the high pressure hose line, is it not opening some valve which would allow the system to suck in more freon?

The only way you're going to get more than half a can of freon into your system in any reasonable amount of time, is by running the compressor. I personally have never seen the need to jumper the cycling switch (and in fact, if you left it that way and you had a leak, your brand new compressor could blow up). The only reason to jumper it is to save time, nothing more. From what I recall, charging my system would take the first full can about 10 minutes to pull in, the subsequent cans would take about 7 or 8 minutes. Yours needs about 3 full cans for a full charge, so just be patient and wait for the compressor to suck it in.

You are charging into the suction (low) side, right?

 

[Gregski]

thanks letsbangout so just put a can on there and even with the compressor turning on and off every few seconds it will still suck in the freon from the can, I think I will buy a better quality short yellow hose from NAPA that goes from the can right into the low service port rather than using my cheap harbor freight gauges and the long middle six foot yellow hose that is attached to them, (that's too much room for air to sit in and re enter the system) and it should be way better than the silly blue one with the gauge on top that comes with some cans when you buy em that way, called a shop today and they quoted me up to $1,200 bucks to have it diagnosed, troubleshot, fixed, evacuated, vacuumed, pressure tested, and re charged. I am trying to do it for a third of that cost myself.

My only worry / concern now is over filling it, but at 25 PSI I am a long ways away from the 60-70 PSI on both sides when equalized and full with engine off. Or the 20-30 PSI low side and 120-170 PSI high side with the engine running and AC on obviously.

 

[gpracer1]

thanks letsbangout so just put a can on there and even with the compressor turning on and off every few seconds it will still suck in the freon from the can, I think I will buy a better quality short yellow hose from NAPA that goes from the can right into the low service port rather than using my cheap harbor freight gauges and the long middle six foot yellow hose that is attached to them, (that's too much room for air to sit in and re enter the system) and it should be way better than the silly blue one with the gauge on top that comes with some cans when you buy em that way, called a shop today and they quoted me up to $1,200 bucks to have it diagnosed, troubleshot, fixed, evacuated, vacuumed, pressure tested, and re charged. I am trying to do it for a third of that cost myself.

My only worry / concern now is over filling it, but at 25 PSI I am a long ways away from the 60-70 PSI on both sides when equalized and full with engine off. Or the 20-30 PSI low side and 120-170 PSI high side with the engine running and AC on obviously.

Just so you know, the static pressure of freon ( when the compressor is off) is equal to the temp of said freon. It does not matter if you have 2 cans in the system or 13 cans, it is the same. Therefore you can't gauge how much is in it unless the ac is running.
Even then the low and high side readings need to be compared to an ambient temp graph for 134a.
This is why you really need to know what you are doing if you want ice cold ac.

 

[jayman8200]

I dont want to hijack the thread, but since we are talking about AC, I have a question. I have a leak somewhere in my system and cannot find it. my system was completely empty, so i put 1 can of with green dye in it and would kick on and off. the next day i went and got more thinking it wasnt cycling through the whole system, got an 8oz can with red dye and sealant, put a can of oil in it first, then put 3 reg cans of freon and got it fully charged, blowing good out of the vent, a day later it is warm again, but i cannot find any dye on any of the lines. are there any diagrams of the entire ac system to see if i am missing any?

 

[JenneK]

Probably your evap core. Remove the HVAC fan and look towards the left. Maybe you'll be able to spot the dye.

 

[gpracer1]

Probably your evap core. Remove the HVAC fan and look towards the left. Maybe you'll be able to spot the dye.

Yup, that would suck. Also check the front of the compressor by the clutch.

 

[jayman8200]

ok, i pulled out the blower fan to look at the evap core and didnt see any dye. i am so dumbfounded...the only dye i see is under where i charged it, back of the compressor..i think it was spray from when i was charging, but could it leak from back there?

 

[jayman8200]

where are the lines for the rear that i can check to see if maybe it is leaking out of there. since i cant find the dye there maybe it is coming out of the rear air...does anyone have any diagrams on the rear ac system?

 

[Gregski]

I dont want to hijack the thread, but since we are talking about AC, I have a question.

Hijacker !!! LOL, jk

---------- Post added at 07:58 PM ---------- Previous post was at 07:57 PM ----------

Don't want to beat a dead horse to death, but often times a thread sounds like just what your problem is and then you never see what happened, what the solution was, well this won't be that thread, I won't let it.

So with the system reading 25 PSI on the low side and 25 PSI on the high side with the vehicle idling, I threw in the towel and took in to a shop, an independent shop not the stealership.

Here's what they found, when they measured the pressure they said it was 11 PSI on the low side and 100 PSI on the high side, with the engine idling at 2,000 RPM. So basically low on freon.

Well first lesson is that the Harbor Freight gauges are ****. Not only do they read incorrectly but they only go up to 36 PSI on the low side and 90 PSI on the high side for 134R. The pro gagues go up to 300 on the low side and 500 on the high side, but more importantly read accurately.

The second lesson is that we need to have the rig reved up to 2,000 RPM to take accurate measurements.

So for $230 bucks (the cost of a decent gauge set) they evacuated my system, pulled a vacuum, checked for leaks (using two methods, vacuum, and a $600 dollar leak detector) and filled the system. No leaks were found!

Now the Low Port Pressure is - 25
High Port Pressure is - 150
Ambient Temp was - 75
Center Vent Temp blows - 40

Third lesson, in my opinion a 12 oz can is no 12 ounces. Neither can you fill up your system from completely empty with those stupid cans, it may take 7 cans or so, plus you get air in the line every time you swap a can. So they may be ok for topping off a system when it's a little low but that's about all. Think of spray cans of paint, you can paint some chassy parts with it but you wouldn't paint a car with them. (Flat black excluded, LOL)

I hope this information and bench marks help someone in the future, I sure learned a lot. I don't normally mention the name of the shop but in this case Polar Bear Auto Care gets my big thanks as do all of you for reading and trying to help, stay cool!