How do you read a/c manifold gauges?
08-24-2003, 09:26 PM
#1
Racer
Thread Starter
How do you read a/c manifold gauges?
Starting to learn about the a/c system on my '91 and bought manifold set. However, the instructions are less than clear.
I figured out how to connect it to the car, but not sure if I'm reading/using the manifold correctly. Here's what I did, and please tell me if this is right/wrong or what...
Closed red and blue handwheel valves on manifold.
Opened red and blue **** valves at the end of each read and blue hose.
Connected loose end of the yellow hose onto its nipple on the manifold.
Connected red and blue hoses to fittings on a/c system (nice they are different sizes and you can't screw it up).
Started engine, engaged a/c compressor button. Compressor running fine.
Opened red and blue handwheel valves on manifold 1.5 turns each (per instructions).
Both read and blue gauges stablized at almost exactly 140 psi each?!?
Something ain't right...I'm too low on the high side, and too high on the low side from what I've read, OR, I'm not doing something right.
So, if I did use the tool correctly, what is the likely problem? If I did not use the tool correctly, please tell me how.
All help/suggestions are welcome.
I figured out how to connect it to the car, but not sure if I'm reading/using the manifold correctly. Here's what I did, and please tell me if this is right/wrong or what...
Closed red and blue handwheel valves on manifold.
Opened red and blue **** valves at the end of each read and blue hose.
Connected loose end of the yellow hose onto its nipple on the manifold.
Connected red and blue hoses to fittings on a/c system (nice they are different sizes and you can't screw it up).
Started engine, engaged a/c compressor button. Compressor running fine.
Opened red and blue handwheel valves on manifold 1.5 turns each (per instructions).
Both read and blue gauges stablized at almost exactly 140 psi each?!?
Something ain't right...I'm too low on the high side, and too high on the low side from what I've read, OR, I'm not doing something right.
So, if I did use the tool correctly, what is the likely problem? If I did not use the tool correctly, please tell me how.
All help/suggestions are welcome.
08-25-2003, 02:28 AM
#2
Rennlist Member
Robert,
Its been a long time but on my guages you don't open the valves on the manifold to read the High/Low pressures, you will be bypassing the compressor and getting the same reading on both. You only use those when you are adding freon, bleeding or pulling a vacuum.
Be careful in adding too much refrigerant if you are dealing with false readings you can do some serious damage.
Anyway, one side sucks and the other side blows, so have fun and don't overdo it
Its been a long time but on my guages you don't open the valves on the manifold to read the High/Low pressures, you will be bypassing the compressor and getting the same reading on both. You only use those when you are adding freon, bleeding or pulling a vacuum.
Be careful in adding too much refrigerant if you are dealing with false readings you can do some serious damage.
Anyway, one side sucks and the other side blows, so have fun and don't overdo it
07-20-2014, 11:00 AM
#3
The hoses should be attached to the service manifold (thing with the gauges and ***** on it) before you attach the hoses to the vehicle.
Depending upon the design of the hose connections at the manifold (most are the same since there are only a handful of mfg's today) insure the rubber gasket inside the end of the hose fitting, which attaches to the manifold, is present. If you over tighten the connection you can shear the gasket.
The Red hose connects to the high side port on the manifold gauge set.
The Blue hose connects to the low side port on the manifold gauge set.
Usually a yellow hose connects to the vacuum/charge port on the gauge set, and if you have a 4 port gauge yellow will be for charging and black for vacuum (most of the time but ya never know).
The manifold gauge valves, valves on the service manifold, should be turned in (CW, right) for their closed position, to take readings of the vehicle's low and high side pressures. As J noted, the only time you have these valves open is to evacuate or charge the system. For a DIY I'd suggest only charging through the low side, meaning the high side valve will always be closed except for when you are evacuating or pulling a vacuum.
With the vehicle engine off:
The Red hose end with the "service coupler" connects to the high side on the vehicles ac system. The Blue hose connects to the low side.
There are basically 2 variations of service couplers for R134a systems: A coupler with a **** you can turn (a valve) and one without. The versions with a **** must be turn outward (CCW, left) before you attempt to connect to the vehicle's service port because the **** moves a pin inside the coupler that presses in the schrader valve on the R134a service port on the vehicle and if you attempt to attach it with the pin extended you can release refrigerant from the vehicle system or you could damage the schrader valve.
The couplers are a 'snap type'; alike coupler for an air hose tool. You pull back the outer ring on the coupler, insert the coupler straight on vehicles R134a service port, press down until it seats, release the outer ring and it should remain affixed; you can't pull it off.
The high side service port on the vehicle's system will be located either on the compressor's discharge manifold (where your vehicle's ac hose connects), a place on the compressor adjacent to the high side or discharge side, on a fitting or hose connected to the high side of the compressor, or anywhere between the discharge of the compressor and the expansion valve. Now that is a lot of possibilities but for your situation if you have a 964 the high side port will be near on or near the compressor's hose manifold. Service ports usually have a dust cap and vehicle mfg's are not particular on the color to symbolize what is what, but if you see a Red color dust cap its usually the high side. High side R134a service port fittings are larger in outer diameter than the low.
The low side service port on the vehicle's system will be located either on the compressor's suction manifold (where your vehicle's ac hose connects), a place on the compressor adjacent to the low side or suction side, on a fitting or hose connected to the low side of the compressor, or anywhere between the suction side of the compressor and the evaporator outlet. Ditto on a lot of possibilities but for a 964 the low side port will be on or near the compressor's hose manifold. Low side R134a service port fittings are smaller in outer diameter than the high.
After you have connected the service hoses to the vehicle, insuring they are not going to get in the way of the compressor's clutch pulley, and insuring the valves on the service manifold are all closed, and if you snap connectors have **** valves .... open them (CW right), if your vehicle has refrigerant in it you should see positive (greater than zero) gauge readings and with the engine off the low and high will both read the same because the system is "equalized". The value or degree above the zero mark will all depend upon if the system is fully charge and the ambient (outside) air temperature because the high the temperature the greater the value will be (heat expands gases).
Start the engine, turn on the ac system to max cold, look at the compressor clutch's outer hub, it should be turning in unison with the pulley if things are working, and watch the gauges. In a properly working system the high side value will be much greater than the low. How high the high side will be is based upon the amount of refrigerant in the system, the outside air temperature, whether the clutch is engaged (thermostat is calling for 'demand'), and a few other factors; we use T&P charts (temperature and pressure relational charts dependent upon refrigerant type) to evaluate what is happening. The low side will typically be above, zero, somewhere between 20 and 40 if everything is normal. The suction hose fitting, between the evaporator and compressor inlet, will be sweating or cold, and the high side hose fitting, between the compressor outlet and the condenser up front, will be hot.
Those are just the basics. I probably have a half dozen different types and brands of service sets. Each has its pro's and con's in design. Some were defective 'out of the box'; a gauge 50 psi off spec, leaking site glasses, faulty one way valves, etc. So like any tool, you need to know the tool before you use it or rely on it.
You can do a great job on a great day. Try to do it when your tired, trying to multitask a bit too much, while having customer's look over your shoulder, can end in bad results. So, take your time, plan it out, think as you go along, and write things down (document your observations).
I'd suggest a set of safety glasses when servicing. Liquid refrigerant and refrigerant oil getting in your eyes can really mess up your day.
I don't "discouraged" DIY's from servicing their own AC systems. It can be fun and rewarding, but if you add up the cost of having the proper tools, the learning curve, and errors that happen along the way, sometimes its best to leave it to a pro and just move on to another project.
I'd provide you with some helpful links but the moderator/police have a new business model here now, unlike the founder, and have too much spare time on their hands and just love to hit the delete button, lol.
Depending upon the design of the hose connections at the manifold (most are the same since there are only a handful of mfg's today) insure the rubber gasket inside the end of the hose fitting, which attaches to the manifold, is present. If you over tighten the connection you can shear the gasket.
The Red hose connects to the high side port on the manifold gauge set.
The Blue hose connects to the low side port on the manifold gauge set.
Usually a yellow hose connects to the vacuum/charge port on the gauge set, and if you have a 4 port gauge yellow will be for charging and black for vacuum (most of the time but ya never know).
The manifold gauge valves, valves on the service manifold, should be turned in (CW, right) for their closed position, to take readings of the vehicle's low and high side pressures. As J noted, the only time you have these valves open is to evacuate or charge the system. For a DIY I'd suggest only charging through the low side, meaning the high side valve will always be closed except for when you are evacuating or pulling a vacuum.
With the vehicle engine off:
The Red hose end with the "service coupler" connects to the high side on the vehicles ac system. The Blue hose connects to the low side.
There are basically 2 variations of service couplers for R134a systems: A coupler with a **** you can turn (a valve) and one without. The versions with a **** must be turn outward (CCW, left) before you attempt to connect to the vehicle's service port because the **** moves a pin inside the coupler that presses in the schrader valve on the R134a service port on the vehicle and if you attempt to attach it with the pin extended you can release refrigerant from the vehicle system or you could damage the schrader valve.
The couplers are a 'snap type'; alike coupler for an air hose tool. You pull back the outer ring on the coupler, insert the coupler straight on vehicles R134a service port, press down until it seats, release the outer ring and it should remain affixed; you can't pull it off.
The high side service port on the vehicle's system will be located either on the compressor's discharge manifold (where your vehicle's ac hose connects), a place on the compressor adjacent to the high side or discharge side, on a fitting or hose connected to the high side of the compressor, or anywhere between the discharge of the compressor and the expansion valve. Now that is a lot of possibilities but for your situation if you have a 964 the high side port will be near on or near the compressor's hose manifold. Service ports usually have a dust cap and vehicle mfg's are not particular on the color to symbolize what is what, but if you see a Red color dust cap its usually the high side. High side R134a service port fittings are larger in outer diameter than the low.
The low side service port on the vehicle's system will be located either on the compressor's suction manifold (where your vehicle's ac hose connects), a place on the compressor adjacent to the low side or suction side, on a fitting or hose connected to the low side of the compressor, or anywhere between the suction side of the compressor and the evaporator outlet. Ditto on a lot of possibilities but for a 964 the low side port will be on or near the compressor's hose manifold. Low side R134a service port fittings are smaller in outer diameter than the high.
After you have connected the service hoses to the vehicle, insuring they are not going to get in the way of the compressor's clutch pulley, and insuring the valves on the service manifold are all closed, and if you snap connectors have **** valves .... open them (CW right), if your vehicle has refrigerant in it you should see positive (greater than zero) gauge readings and with the engine off the low and high will both read the same because the system is "equalized". The value or degree above the zero mark will all depend upon if the system is fully charge and the ambient (outside) air temperature because the high the temperature the greater the value will be (heat expands gases).
Start the engine, turn on the ac system to max cold, look at the compressor clutch's outer hub, it should be turning in unison with the pulley if things are working, and watch the gauges. In a properly working system the high side value will be much greater than the low. How high the high side will be is based upon the amount of refrigerant in the system, the outside air temperature, whether the clutch is engaged (thermostat is calling for 'demand'), and a few other factors; we use T&P charts (temperature and pressure relational charts dependent upon refrigerant type) to evaluate what is happening. The low side will typically be above, zero, somewhere between 20 and 40 if everything is normal. The suction hose fitting, between the evaporator and compressor inlet, will be sweating or cold, and the high side hose fitting, between the compressor outlet and the condenser up front, will be hot.
Those are just the basics. I probably have a half dozen different types and brands of service sets. Each has its pro's and con's in design. Some were defective 'out of the box'; a gauge 50 psi off spec, leaking site glasses, faulty one way valves, etc. So like any tool, you need to know the tool before you use it or rely on it.
You can do a great job on a great day. Try to do it when your tired, trying to multitask a bit too much, while having customer's look over your shoulder, can end in bad results. So, take your time, plan it out, think as you go along, and write things down (document your observations).
I'd suggest a set of safety glasses when servicing. Liquid refrigerant and refrigerant oil getting in your eyes can really mess up your day.
I don't "discouraged" DIY's from servicing their own AC systems. It can be fun and rewarding, but if you add up the cost of having the proper tools, the learning curve, and errors that happen along the way, sometimes its best to leave it to a pro and just move on to another project.
I'd provide you with some helpful links but the moderator/police have a new business model here now, unlike the founder, and have too much spare time on their hands and just love to hit the delete button, lol.
07-20-2014, 01:00 PM
#4
Rennlist Member
$100 to have a mobile A/C guy come and check out my system and recharge. I figured I would put my energy into fixing leaks or taking apart entire car to get to evaporator.
I admire you for taking this on yourself.
Ricardo
I admire you for taking this on yourself.
Ricardo
07-20-2014, 01:37 PM
#5
Nordschleife Master
$100 is a good price, especially for mobile service. Most places around here, anything having to do with a/c recharge starts at $140 and goes up from there, and it's not mobile.
07-20-2014, 04:28 PM
#6
Addict
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A/C work is quite easy with a set of gauges and a vacuum pump. There are numerous videos online that will explain a lot about using them. There are a lot of precautions you need to take, but it is not rocket science.
