HOW TO- Depressurize AC system?
Thread Starter
Former Vendor
Joined: Mar 2003
Posts: 18,666
Likes: 395
From: Tampa FL
St. Jude Donor '07-'08-'09-'10-'11-'12'-'13-'14-'15
HOW TO- Depressurize AC system?
I need to recharge my AC system (not blowing cold air) but have been told I need to depressurize it before adding coolant. How do I do this?
Also what coolant was used in a 1999? R34 or something else? Thanks
Cajun
Also what coolant was used in a 1999? R34 or something else? Thanks
Cajun
Burning Brakes
Joined: Sep 2003
Posts: 1,085
Likes: 0
From: Broken Arrow OK
Your car uses R134a refrigerant. Don't see why you would need to depressurize to add additional refrigerant. Before you start looking at adding refrigerant, first check to see if the A/C belt has broken. My 99 quit cooling last year and I was about to start checking the A/C system pressure when I noticed that the A/C drive belt was broken.
Thread Starter
Former Vendor
Joined: Mar 2003
Posts: 18,666
Likes: 395
From: Tampa FL
St. Jude Donor '07-'08-'09-'10-'11-'12'-'13-'14-'15
Your car uses R134a refrigerant. Don't see why you would need to depressurize to add additional refrigerant. Before you start looking at adding refrigerant, first check to see if the A/C belt has broken. My 99 quit cooling last year and I was about to start checking the A/C system pressure when I noticed that the A/C drive belt was broken.
Cajun
Team Owner
Joined: Apr 2001
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From: S.W. Ohio. . . . . . NRA Life Member
have been told I need to depressurize it before adding (refrigerant).
If a shop were to do the work; then yes... it's best to remove the existing R134a. The draw a vacuum on the system as it is re-charged.
For DIY years ago; you would release the existing refrigerent because the cans of gas available to the home mechanic didn't contain any lubricant. So the DIYer would release all the existing gas, add one container of special refrigerant oil, then start filling with cans of the R12 gas.
Todays DIYer doesn't need to worry about that... as the R134a cans have the proper amount of lubricant included in the R134a can (at least I've never seen one that didn't have the lubricant included in the mix).
So if you use R134a gas with lubricant, then you don't need to completely empty the system first.
Burning Brakes
Joined: Apr 2007
Posts: 966
Likes: 9
From: Phoenix AZ
You say the system has good pressure. How was this determined? If the system pressure is where it needs to be, then you don't want to add anymore refrigerant. R134a doesn't "go bad" over time, so an evac/recharge won't do much good if you already have the proper amount in the system. If it's low, however, then adding some will definitely help.
Rocco
Advanced
Joined: Mar 2005
Posts: 90
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From: Tyngsborough Mass
To properly check a/c operation you should put a set of rerigeration gauges on the system and see what the operating pressures are. Pressure will vary depending on outside air temp cabin air temp. Typically suction side (blue gauge) will read between 30 - 60 psig, discharge (red gauge) will read between 175 - 275 psig at idle. You can also put a meat thermometer in the middle vent with the system running on max with the air recirculating you should have approx a 15-20 deg temp drop from what the return air temp is to the outlet temp. Under hood the large line returning to the a/c compressor should be relativly cold 40 - 50 degs F. These are basic reules of thumb and use them as a HVAC/R tech. If you are unsure about the charging the system my advice would be to find a reputable repair facility to do the work. Good Luck
Melting Slicks
Joined: Feb 2006
Posts: 2,938
Likes: 62
From: Columbia SC
My 00 vert was blowing warm air, put guages on and indicated low coolant. Rechaged system and now blows cold air. No need to depressureize unless you have other issues. 
Last edited by Fast Cop; May 9, 2008 at 10:21 AM.
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From: Olympia Washington
I would suggest taking it somewhere to have it charged, over filling can cause problems also. They discharge it and will pull a vacumn on it to see if you have any leaks. I don't think you can buy small cans of 134A anymore, and how would you know when it was full. You need guages to install freon and check pressures so you don't overcharge.
Thread Starter
Former Vendor
Joined: Mar 2003
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From: Tampa FL
St. Jude Donor '07-'08-'09-'10-'11-'12'-'13-'14-'15
I would suggest taking it somewhere to have it charged, over filling can cause problems also. They discharge it and will pull a vacumn on it to see if you have any leaks. I don't think you can buy small cans of 134A anymore, and how would you know when it was full. You need guages to install freon and check pressures so you don't overcharge.
I will trust you guys and take it to a shop to get it recharged. Thanks for the input.
Cajun
Tech Contributor
Joined: Dec 1999
Posts: 32,910
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Cajun
Theres NO NEED to depressurize your system. You would need to depressurize if you thought that the system was contaminated with moisture and non condensible gasses (AIR). If your system has pressure in it, all it needs is some more R-134.
YES!!! There are correct ways of determining when you have the correct amount of R-134. You do need at a minimum,, a set of gages to read the compressor suction side pressure and the discharge pressure. The service manual has TWO pages of pressure parameters for a correct operating system. It varies with changes in :
Outside temperature
Humidity
Engine RPM
Evaporator output temp (center Duct Temp)
Once you plug those parameters into the chart, you will see what pressures that are correct. If there low, you need to add freon until there correct. I normally purchase R-134 with oil to add oil to the system. If you have a slow leak,,, there a chance that it is also leaking refrigerant oil also. Adding a small amount of oil will not hurt the system. Any extra oil will be deposited in the accumulator/dryer.
Unless you want to gamble and add a quick can of R-134, I agree,,,let a shop do it.
Call me or PM Me. Ill hook you up with some more cool info!
BC
Theres NO NEED to depressurize your system. You would need to depressurize if you thought that the system was contaminated with moisture and non condensible gasses (AIR). If your system has pressure in it, all it needs is some more R-134.
YES!!! There are correct ways of determining when you have the correct amount of R-134. You do need at a minimum,, a set of gages to read the compressor suction side pressure and the discharge pressure. The service manual has TWO pages of pressure parameters for a correct operating system. It varies with changes in :
Outside temperature
Humidity
Engine RPM
Evaporator output temp (center Duct Temp)
Once you plug those parameters into the chart, you will see what pressures that are correct. If there low, you need to add freon until there correct. I normally purchase R-134 with oil to add oil to the system. If you have a slow leak,,, there a chance that it is also leaking refrigerant oil also. Adding a small amount of oil will not hurt the system. Any extra oil will be deposited in the accumulator/dryer.
Unless you want to gamble and add a quick can of R-134, I agree,,,let a shop do it.
Call me or PM Me. Ill hook you up with some more cool info!
BC
Last edited by Bill Curlee; May 9, 2008 at 11:58 AM.
Thread Starter
Former Vendor
Joined: Mar 2003
Posts: 18,666
Likes: 395
From: Tampa FL
St. Jude Donor '07-'08-'09-'10-'11-'12'-'13-'14-'15
Here are the codes from my HVAC:
B0338 H C- Inside Air Temp Sensor Open
B0361 H- Left Actuator Feedback Short to GND
B0441 H- Left Actuator Out of Range
See anything that would cause this issue? Thanks
Cajun
B0338 H C- Inside Air Temp Sensor Open
B0361 H- Left Actuator Feedback Short to GND
B0441 H- Left Actuator Out of Range
See anything that would cause this issue? Thanks
Cajun
Melting Slicks
Joined: Jul 2006
Posts: 3,356
Likes: 1
From: Chesapeake Va
The quickest and easiest way to determine if the system is low, is to just feel the low pressure lines to see if they are cold (as the AC is running, of course). I know its a bit caveman, but it works. As the system looses refrigerant, it will start to loose cooling on the low side (larger lines) from the compressor first, and then working its way back towards the evap, and then all the way to the orifice tube. You dont need to know how to read the gauges, or understand the pressures or nothing. The first place they loose cooling is at the compressor, and at the bottom of the accumulator.
If its full, the entire low side will be of uniform temp. This check works with any AC system.
16 years in FLA, I've done a ton of AC.
PS, I know you cant really get to the back of the compressor, but if you can look at the low side line with a flash light, if its sweating at the compressor, you're good. If the low side line is not sweating at the compressor, its low on freon.
tricks of the trade............
If its full, the entire low side will be of uniform temp. This check works with any AC system.
16 years in FLA, I've done a ton of AC.
PS, I know you cant really get to the back of the compressor, but if you can look at the low side line with a flash light, if its sweating at the compressor, you're good. If the low side line is not sweating at the compressor, its low on freon.
tricks of the trade............
Last edited by edcmat-l1; May 9, 2008 at 09:45 PM.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Cajun
B0338 H C- Inside Air Temp Sensor Open
Theres one problem that keeping it from functioning properly!!!
The sensor is NEXT to your ignition switch. Pull it out and make sure its plugged into the wiring harness.
The other DTC can be cleared by using the following procedure:
Fix the B0338 H C- Inside Air Temp Sensor Open. Then turn the HVAC system OFF. Pull up the DTC for the HVAC system and clear them. Once there cleared, you will / should hear the actuators cycle through there ranges. Once they stop cycling check and make sure the DTCs are still cleared. Then turn the the HVAC unit on and to cool and see if the DTCs come back. I had to do this 4-5 times before my actuators cycled enough to work properly. No problems for over 6 months.
You have my cell #, don't hesitate to call.
PS,,,,,edcmat-l1,,, that method really does work! So simpel, even a cave man can do it.
BC
B0338 H C- Inside Air Temp Sensor Open
Theres one problem that keeping it from functioning properly!!!
The sensor is NEXT to your ignition switch. Pull it out and make sure its plugged into the wiring harness.
The other DTC can be cleared by using the following procedure:
Fix the B0338 H C- Inside Air Temp Sensor Open. Then turn the HVAC system OFF. Pull up the DTC for the HVAC system and clear them. Once there cleared, you will / should hear the actuators cycle through there ranges. Once they stop cycling check and make sure the DTCs are still cleared. Then turn the the HVAC unit on and to cool and see if the DTCs come back. I had to do this 4-5 times before my actuators cycled enough to work properly. No problems for over 6 months.
You have my cell #, don't hesitate to call.
PS,,,,,edcmat-l1,,, that method really does work!
So simpel, even a cave man can do it. BC
20, 2008, ac, az, compressor, corvette, depressure, depressurize, high, hvac, invo, low, refrigerant, side, system, tech
