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.

 

[Gregski]

first I tried the trick of shortening the low pressure clutch cycling switch (well technically the plug that goes to it) that did get the compressor clutch to engage and stay engaged but that did not suck in any more freon from the cans

then I replaced the low pressure clutch cycling switch (located in the accumulator) just for the heck of it, it was only a $20 dollar part

then I replaced the entire compressor for a brand new one, that's right $200 bucks, put the system back together and vacuumed it, then tested for vacuum and it held it perfectly for 45 minutes, the vacuum sucked in some freaon from the first can but won't take any more than a 2/3 of a can, clutch does the same thing cycles on for 5 seconds then shuts off and repeats

help, what is wrong with this system?

 

[clkelley]

I don't mean to sound condescending, but if I am not mistaken, when you put pressure in the system with the vacuum, you should release that pressure before charging with the freon right? Those that I have charged would suck in all I would give them as long as they weren't already pressurized...

 

[Gregski]

... when you put pressure in the system with the vacuum, you should release that pressure before charging with the freon right?

Huh? I hope you are mistaken, LOL, and no you don't sound condescending you are just trying to help and I appreciate that, but first of all you don't put pressure in the system with a vacuum you remove it at least that's how my brain understands it. Now if that vacuum sucked in four 12 oz cans of freon I would be concerned, but it barely takes in 2/3rds of a can so it can't be over filled is my reckoning.

I think I need a better set of gauges than my Harbor Freight ones

 

[clkelley]

lo,, yeah, I was actually the one thinking backwards there. I have honestly never put the systems under vacuum to add freon, just charged them with the low side pressure line like you mentioned and the blue line gauge and a can. Usually worked fine with one to two cans of freon.

 

[Gregski]

bud I have charged my other car, my mamas car, a co workers Mustang at work in the parking lot mind you, even this car in the past and my buddy used my gauges last weekend to charge his Subaru and it all worked as prescribed, so WTF people, LOL

here's an article I am considering for those poor souls reading this in the future

http://www.bsntech.com/bsntech-blog...ycling-on-and-off-in-car-air-conditioner.html

 

[clkelley]

Lol, I hear ya. Considering the parts you have replaced, it has me stumped, of course that isn't saying much, I am kind of a "Jack of all trades, master of none" so to speak...,lol

 

[lesterl]

I always pull a vacume on a very low system, if they just need a couple ounces I just charge it. I try to pull 30 psi of vac for 1/2 hr (I did 1hr on my tahoe because it sat in a field for a few years.) I usually can only get 28 on my guage with the little water fountain compressor I use to suck 'em down, my guage wont even show 40 psi of vac, stops at 30.....

IDK about this blue base cap for the cans, I use a brass can tap you can buy at the parts store, just bought one a month or so ago as I wore the old one out. If it isnt pulling freon in, what pressure does it sit at with the guage on it, engine off?

 

[Gregski]

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 sh!t. 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!

 

[lesterl]

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.

THANKS!

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.

Those readings indicate low and no compressor activation.

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.

There ya go!

Well first lesson is that the Harbor Freight gauges are sh!t. 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.

I have used my HF guage set ALOT..... only had issues on 1 car and it was a conversion from R12 (that I had done.)

The second lesson is that we need to have the rig reved up to 2,00 PSI to take accurate measurements.

What do you mean by revved up to 2,00 PSI?

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 use my HF set of guages and have a compressor hooked to high side port, I suck the whole gauge set down with all lines hooked up (the valves at the cars low side service port is closed, I have a can of freon attached to the charge port on the guage set), when sucked down I shut off the high side valve, pierce the can, open the low side ports, only freon gets into the system, when that can is expired, I close the guage Low port, attach a new can, open high side (vac lines down), then repeat process to finish charging. I plan on making an attachment to hook a set of secondary valves to the charge port so I can use the High side guage for more than troubleshooting.


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!

Thanks, sounds like you got some good results. My Hoe I sucked her down for 1 hour (sat in a field for 6 years), no leaks so I charged 3 cans and I can get high 30's out of middle vent in 70* weather, since it is around 100 here lately I get very low 40's.........

 

[Gregski]

What do you mean by revved up to 2,00 PSI?

2,000 RPM sorry, PSI / RPM what's the difference :uhoh2: it blows cold that's all that matters, LOL

 

[lesterl]

Didnt know if you had the compressor on high side to 200 or the RPM @ 2k..... Cold air RULZ!!!!!