Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner

1 - 20 of 23 Posts

·
Registered
2002 chevy trailblazer_ls
Joined
·
19 Posts
Discussion Starter #1
hey guys

the first thing that started was my compressor clutch was not engaging. i searched the website and found out that it may be the pressure switch. so i replaced it and nothing happened. next i tried to recharge my A/C with a can from autozone. during the first part of the recharge the clutch started engaging again. so i was happy for about two seconds cause everytime the clutch engages it drags the rpm down to an almost stall then disengages and rpm returns to normal and the pressure on the gauge on the can of recharge stuff went way into the red. so i unplugged the hose shut it off and walked away.

any ideas as to what my be causing the erratic behavior?
 

·
Registered
2002 gmc envoy_slt
Joined
·
539 Posts
Everytime your guage goes into the red at the same time the compressor shuts off, it's the can pressure that's pushing it up. If you don't have a full set of guages, it's almost impossible to tell what's really happening. It's worth spending the $60.00 or so to get a diagnostic done at an AC shop if you really don't know that much about AC systems. One slip up and you might be buying a new compressor for yourself. That quickly goes to a $1000 repair. HTH c good
 

·
Registered
2002 gmc envoy_sle
Joined
·
98 Posts
Sounds like you are still low on refrigerant. When you were adding refrigerant the pressure came up on the low side & this caused the low pressure switch to set, then your compressor came on. Your low side pressure then immediately dropped (because your still undercharged) & the compressor turned off. Get 1 more can of R134a refrigerant that also has 2 ounces of refrigeration oil in it & add to system. The loss of refrigerant also results in a loss of oil. You need this oil to lubricate the compressor & its shaft seal. Its normal for the compressor to cycle on the low pressure cut out when ambient is low and/or blower fan speed is set to low.
 

·
Registered
2002 chevy trailblazer_ls
Joined
·
19 Posts
Discussion Starter #5
i didnt get the whole can in the system before i stopped. i will try to put the whole can in and see what happens.
 

·
Registered
2002 gmc envoy_sle
Joined
·
98 Posts
I believe this will solve it. Make certain the can of refrigerant also has 2 ounces of oil in it. Lack of lubrication in your compressor(due to oil loss) will cause a sudden drop in idle speed. Erratic idle during a/c clutch engagement could also be due to dirty throttle body. If your a/c clutch currently is still not engaging it will take at least 1 full can(12 ounces) to top it off. Reply back with results.
 

·
Registered
2002 chevy trailblazer_ls
Joined
·
19 Posts
Discussion Starter #8
ok the original can of recharge i got was 18oz. i just went outside to put the rest of the can in the system to see what would happen. once i started my vehicle and turned the a/c on, the compressor didnt engage. once i started the recharge it started working again and took the whole can. the can didn't contain any oil so i will go tomorrow and get one that has oil in it and try it again. every time the clutch engaged, the rpm still dropped. gonna clean the throttle body tomorrow as well.
 

·
Registered
2002 chevy trailblazer_ls
Joined
·
19 Posts
Discussion Starter #9
also, i purchased a 12oz can for my girlfriends ranger and had no problems recharging her system. so i am confident i didnt do anything wrong with my TB and its got to be something mechanical.
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
107 Posts
My TB was doing the same thing wgen the compressor engaged. I have to clean mine, the computer learned to compensate for the dirty TB after a few days. I bought the PCM for less tune and will be sending the puter out when I get my Z28 back out. Figured it would be a good time to clean it. The ac system either takes 2 lbs of freon or 3, depending on the model. Remember, putting in to much freon is worse than not enough and do not turn the can upside down while the car is running, this can blow the vavles out of the compressor.
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
107 Posts
Without a scale for freon, you can not be perfect, but 16 oz per pound is close enough. Just watch the the gauge on the freon can. Have the car about 1500 to 1700 rpm's while charging. A trick to tell if there is not enough freon in the system, the accumulator and the suction hose will form ice on them.
 

·
Registered
2002 gmc envoy_sle
Joined
·
98 Posts
There is a good chance that the drop in idle speed during a/c clutch engagement is due to your compressor seizing due to lack of oil. The oil travels with the refrigerant, when you have a leak and loose refrigerant you also loose oil. The oil also lubricates the compressor shaft seal and can stop a leak at the seal which is common. You need to be certain at this point that you are not overcharging the system. Your low side pressure should not be more than 35 psi at idle with compressor engaged. The high end of the green scale on most D.I.Y. drop in cans of refrigerant w/gauge is in this range. You probable still need to clean throttle body also. Its also possible that you are leaking refrigerant as fast as you add it. You need to determine what the low side pressure is before & after A/C clutch engagement. Overcharging the system is dangerous and can cause the high side to rupture.
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
107 Posts
Your low side pressure should not be more than 35 psi at idle with compressor engaged.
If you have it at 35# at an idle it will freeze up, or at least the compressor will be cycling on and off constantly while going down the road. That is a good way to wear out a clutch! You want them to come on and stay on. The The temp you want coming out of the ducts while driving down the freeway is 45 to 50 deg. The rpms will be about 2000 or so.
 

·
Registered
2002 gmc envoy_sle
Joined
·
98 Posts
If you have it at 35# at an idle it will freeze up, or at least the compressor will be cycling on and off constantly while going down the road. That is a good way to wear out a clutch! You want them to come on and stay on. The The temp you want coming out of the ducts while driving down the freeway is 45 to 50 deg. The rpms will be about 2000 or so.
The pressure temperature of R134A at 35 PSI is 40 degrees. This will not cause freeze up or short cycling of compressor nor will it wear out the clutch. There are many instances where the compressor must cycle on the low pressure cut out, if it did not the compressor would be ruined by slugging of liquid refrigerant. The reason the low pressure cut out is there, is to protect the compressor. The best way to charge the system is to recover the refrigerant, evacuate, & weigh in exact charge. When charging with gauges you must take into account: exterior ambient, interior temperature, engine rpm, evaporator blower speed, condenser airflow(cfm), suction line super heat, & latent heat load. The final set pressure on low side is governed by this. You would never charge by simply adding refrigerant until the low pressure cut out could not cycle off. This will cause compressor failure.
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
107 Posts
I am sorry, I thought I read deg not psi. I even typed psi, but brain was reading deg. You are correct. I am impressed you understand super heat and latent heat. Higher pressure will raise the boiling point :suicide:
 

·
Registered
2002 chevy trailblazer_ls
Joined
·
20 Posts
I you are that concerned about it take you car to a shop and have them fully discharge your system and recharge it to the proper level. unless you can get your hands on some gauges and know where the pressuses should be at it dosent make a difference how much freon you drop into a system.
:crackup:
 

·
Registered
2002 gmc envoy_sle
Joined
·
98 Posts
I am sorry, I thought I read deg not psi. I even typed psi, but brain was reading deg. You are correct. I am impressed you understand super heat and latent heat. Higher pressure will raise the boiling point :suicide:
Thanx for clearing that up! Its obvious that you are knowledgeable of refrigeration systems.
 

·
Registered
2002 chevy trailblazer_ls
Joined
·
19 Posts
Discussion Starter #19
ok so in about two hours ima go to autozone and get some compressor oil. if that doesnt work, its going to the shop.
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
107 Posts
Don't just buy compressor oil. Get the freon with compressor oil in it. You should be ok.
 
1 - 20 of 23 Posts
Top