HVAC Perfect but Wrong!!
04-16-2014, 05:11 PM
#41
Tech Contributor
Member Since: Dec 1999
Location: Anthony TX
Posts: 32,736
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CI 6,7,8,9,11 Vet
St. Jude Donor '08
The VETTE season is back for us Arctic Tundra New England dwellers.: thumbs :
So,,,,,, SOON there will be a LOT of people who will have HVAC & AC cooling Issues. I hope this helps get you cool again.
This is a very good post as it explains how the system works. YES,, a LOW R-134 charge is one issue that can cause the drivers vents to blow warm while the passenger’s side is cold/cool. Before you race off to get more R-134, make sure that you don’t have temperature door electric actuator issues.
NOTE! If you have a manual HVAC Control system, you will NOT see actuator error DTCs. The electric actuator DTCs only show up for the Dual Zone System.
When you purchase your R-134 refill, it’s important to get a refill that has Refrigerant Oil in the charge.
As your system loses R-134, some system oil leak can also leak out. Low system oil can damage the compressor. Don’t worry about adding too much oil with the charge. The Receiver Dryer (big silver can on the fire wall behind the battery) holds any extra oil that the system doesn’t use.
If your system doesn’t have any pressure or it’s extremely LOW, It’s HIGHLY RECOMMENDED that you find the leak and repair it. You should also have the system placed under a complete vacuum to remove all of the moisture and non-condensable gasses (air) in the system if it ever gets that low.
If the R-134 system gets moisture in it, acids will form on the inside of the system and the acids will etch tiny pin holes in the aluminum parts of the system. The aluminum parts (Evaporator, Condenser, & the aluminum piping) will rot from the inside out. Then you will need to replace those damaged parts. $$$$$$$$$$
You also have a small orifice restrictor tube/screen in the high pressure side of the system. That orifice tube is what meters and sprays the correct amount of R-134 liquid into the low pressure side of the evaporator coil to start the cooling process. Moisture in the system will cause that screen and tube to sludge up and clog. The small oriface tube is about the same diameter size as an ink pen cartridge and about an inch long. It’s easily clogged if the system gets dirty.
NEVER over pressurize the system! Too much pressure in the system equals compressor death!
Using the proper gage manifold to monitor the high and low side pressures is the correct way to troubleshoot and charge the system.
If you know the system is just a little low, it’s usually easily resolved by a partial recharge or one full recharge if the system needs it. At a minimum find the proper recharge can with a low side pressure gage on the refill hose and make sure that the low side pressure is NOT way out of spec high.
Add a little R-134 gas to the system and shut the valve on the can to see what the low side pressure is. Continue to add and monitor until the proper low side pressures are obtained. You cannot read the low side system pressure when the can is filling the system. You have to close the valve on the can to see the actual low side system pressure. If the system pressure is really low out of spec, the compressor will NOT operate until the system pressure is above the safety cut off pressure. When you add R-134 and the pressure increases, the compressor will run once you get above the cut off pressure.
To properly read the low side system pressure during the charge process, the engine RPM needs to be held at a steady @ 1000 RPM (you will need an assistant to sit in the car to operate the throttle).
Have the HVAC Fan on full speed, full cold on the temp ****/s, both doors open and blowing out of the center & upper vents. That placed the proper load on the evaporator coil.
Outside Humidity and ambient outside temperature plays a big part on system pressure. Use the chart to figure out what pressures that you should actually see on both sides of the system.
ALWAYS charge the low side with the top of the recharge can in the UP position. If you turn recharge the can up-side down, you will be adding LIQUID R-134 to the GAS side of the system. Your compressor will NOT like that at all!!!
It can cause the rings on the compressor pistons to be damaged.
You can also sit the recharge can (top of the can UP) in a small pail/container of hot tap water and that will speed up the charge process. It helps the R-134 liquid in the pressurized can to boil off and change into a gas. The R-134 gas is what the low side needs.
The low side charge Schrader Valve (back near the battery area, between the battery plastic surround and the passenger side of the engine) is a different size (larger) than the high side Schrader valve which is on the small diameter high pressure line near the front of the coolant reservoir near the frame.
The recharge can hose fitting will not fit on the high side valve. When the system is charged and running, the high pressure piping will be very HOT and the low pressure piping will be very cold.
Measure the cold air temp from the center vent with an accurate gage.
Bill
So,,,,,, SOON there will be a LOT of people who will have HVAC & AC cooling Issues. I hope this helps get you cool again.
This is a very good post as it explains how the system works. YES,, a LOW R-134 charge is one issue that can cause the drivers vents to blow warm while the passenger’s side is cold/cool. Before you race off to get more R-134, make sure that you don’t have temperature door electric actuator issues.
NOTE! If you have a manual HVAC Control system, you will NOT see actuator error DTCs. The electric actuator DTCs only show up for the Dual Zone System.
When you purchase your R-134 refill, it’s important to get a refill that has Refrigerant Oil in the charge.
As your system loses R-134, some system oil leak can also leak out. Low system oil can damage the compressor. Don’t worry about adding too much oil with the charge. The Receiver Dryer (big silver can on the fire wall behind the battery) holds any extra oil that the system doesn’t use.
If your system doesn’t have any pressure or it’s extremely LOW, It’s HIGHLY RECOMMENDED that you find the leak and repair it. You should also have the system placed under a complete vacuum to remove all of the moisture and non-condensable gasses (air) in the system if it ever gets that low.
If the R-134 system gets moisture in it, acids will form on the inside of the system and the acids will etch tiny pin holes in the aluminum parts of the system. The aluminum parts (Evaporator, Condenser, & the aluminum piping) will rot from the inside out. Then you will need to replace those damaged parts. $$$$$$$$$$
You also have a small orifice restrictor tube/screen in the high pressure side of the system. That orifice tube is what meters and sprays the correct amount of R-134 liquid into the low pressure side of the evaporator coil to start the cooling process. Moisture in the system will cause that screen and tube to sludge up and clog. The small oriface tube is about the same diameter size as an ink pen cartridge and about an inch long. It’s easily clogged if the system gets dirty.
NEVER over pressurize the system! Too much pressure in the system equals compressor death!
Using the proper gage manifold to monitor the high and low side pressures is the correct way to troubleshoot and charge the system.
If you know the system is just a little low, it’s usually easily resolved by a partial recharge or one full recharge if the system needs it. At a minimum find the proper recharge can with a low side pressure gage on the refill hose and make sure that the low side pressure is NOT way out of spec high.
Add a little R-134 gas to the system and shut the valve on the can to see what the low side pressure is. Continue to add and monitor until the proper low side pressures are obtained. You cannot read the low side system pressure when the can is filling the system. You have to close the valve on the can to see the actual low side system pressure. If the system pressure is really low out of spec, the compressor will NOT operate until the system pressure is above the safety cut off pressure. When you add R-134 and the pressure increases, the compressor will run once you get above the cut off pressure.
To properly read the low side system pressure during the charge process, the engine RPM needs to be held at a steady @ 1000 RPM (you will need an assistant to sit in the car to operate the throttle).
Have the HVAC Fan on full speed, full cold on the temp ****/s, both doors open and blowing out of the center & upper vents. That placed the proper load on the evaporator coil.
Outside Humidity and ambient outside temperature plays a big part on system pressure. Use the chart to figure out what pressures that you should actually see on both sides of the system.
ALWAYS charge the low side with the top of the recharge can in the UP position. If you turn recharge the can up-side down, you will be adding LIQUID R-134 to the GAS side of the system. Your compressor will NOT like that at all!!!
It can cause the rings on the compressor pistons to be damaged. You can also sit the recharge can (top of the can UP) in a small pail/container of hot tap water and that will speed up the charge process. It helps the R-134 liquid in the pressurized can to boil off and change into a gas. The R-134 gas is what the low side needs.
The low side charge Schrader Valve (back near the battery area, between the battery plastic surround and the passenger side of the engine) is a different size (larger) than the high side Schrader valve which is on the small diameter high pressure line near the front of the coolant reservoir near the frame.
The recharge can hose fitting will not fit on the high side valve. When the system is charged and running, the high pressure piping will be very HOT and the low pressure piping will be very cold.
Measure the cold air temp from the center vent with an accurate gage.
Bill
Last edited by Bill Curlee; 04-16-2014 at 05:25 PM.
04-16-2014, 06:18 PM
#42
Instructor
Thanks to Bill and the other contributors here I got my AC system blowing 40 degrees out of the center vent.
When I got my car it had a new compressor and a few other parts, but no AC. I found the low side Schrader was leaking, so I replaced that and had a professional vacuum and charge done. That worked great for a couple of days until the driver side started blowing warm. I re-indexed the driver side actuator and got cold air again until the charge dropped from a leaking high side Schrader valve. I got the AC Schrader valve replacement without losing charge kit off of ebay and a new valve and since then I have been good. Hope that's it.
I guess the only thing I really wanted to add was if you have a leak look at your Schrader valves, those are real common failure areas.
When I got my car it had a new compressor and a few other parts, but no AC. I found the low side Schrader was leaking, so I replaced that and had a professional vacuum and charge done. That worked great for a couple of days until the driver side started blowing warm. I re-indexed the driver side actuator and got cold air again until the charge dropped from a leaking high side Schrader valve. I got the AC Schrader valve replacement without losing charge kit off of ebay and a new valve and since then I have been good. Hope that's it.
I guess the only thing I really wanted to add was if you have a leak look at your Schrader valves, those are real common failure areas.
05-31-2022, 05:33 PM
#43
Intermediate
R134 solved it
