Correct readins on AC. Need help troubleshooting

[navyjoe]

My AC has slowly started to stop proper cooling. I just came back from a 8500 mile trip out west. I was working fine until we got back to the south (Mississippi) and it began to warm up.

Here are my readings today with outside temp at 91 degrees:

Low side 35 psi
High side 275 psi
Fan on high, engine at idle, in shade, ambient temp 91

Temp at center outlet 60 degrees. Clutch cycled occasionally.

I think the readings are about correct except maybe the low side might be a little low at 91 degrees ambient.

I also expect it could be a damper problem.

Ideas appreciated !!

 

[Bob4x4]

Ambient Air Temperature	21° C (70° F)	27° C (80° F)	32° C (90° F)	38° C (100° F)	43° C (110° F)
Air Temperature at Center Panel Outlet	7° C (45° F)	7° C (45° F)	13° C (55° F)	13° C (55° F)	18° C (64° F)
Compressor Inlet Pressure at Service Port (low Side)	138 to 207 kPa (20 to 30 psi)	172 to 241 kPa (25 to 35 psi)	207 to 276 kPa (30 to 40 psi)	241 to 310 kPa (35 to 45 psi)	276 to 345 kPa (40 to 50 psi)
Compressor Discharge Pressure at Service Port (High Side)	1034 to 1724 kPa (150 to 250 psi)	1379 to 2068 kPa (200 to 300 psi)	1724 to 2413 kPa (250 to 350 psi)	1999 to 2689 kPa (290 to 390 psi)	2413 to 2965 kPa (350 to 430 psi)

 

[petersonj]

was working fine until we got back to the south (Mississippi) and it began to warm up.

Here are my readings today with outside temp at 91 degrees:

Low side 35 psi
High side 275 psi
Fan on high, engine at idle, in shade, ambient temp 91

Temp at center outlet 60 degrees. Clutch cycled occasionally.

I am guessing that the dew point of that 91 degree southern Mississippi air is probably in the low to middle 70's. That additional load alone (caused by the higher dew point than out west) would account for the 60 degree duct air temperature. I would think that the compressor with the additional load should not be cycling at all with the engine at idle. The system may be just a little bit low on refrigerant - otherwise things seem normal.

It was nice that you provided great information.

- John

 

[navyjoe]

Bob, Thanks for the chart. That's fantastic. Where did you get the info?

 

[navyjoe]

Ambient Air Temperature	21° C (70° F)	27° C (80° F)	32° C (90° F)	38° C (100° F)	43° C (110° F)
Air Temperature at Center Panel Outlet	7° C (45° F)	7° C (45° F)	13° C (55° F)	13° C (55° F)	18° C (64° F)
Compressor Inlet Pressure at Service Port (low Side)	138 to 207 kPa (20 to 30 psi)	172 to 241 kPa (25 to 35 psi)	207 to 276 kPa (30 to 40 psi)	241 to 310 kPa (35 to 45 psi)	276 to 345 kPa (40 to 50 psi)
Compressor Discharge Pressure at Service Port (High Side)	1034 to 1724 kPa (150 to 250 psi)	1379 to 2068 kPa (200 to 300 psi)	1724 to 2413 kPa (250 to 350 psi)	1999 to 2689 kPa (290 to 390 psi)	2413 to 2965 kPa (350 to 430 psi)

I am guessing that the dew point of that 91 degree southern Mississippi air is probably in the low to middle 70's. That additional load alone (caused by the higher dew point than out west) would account for the 60 degree duct air temperature. I would think that the compressor with the additional load should not be cycling at all with the engine at idle. The system may be just a little bit low on refrigerant - otherwise things seem normal.

It was nice that you provided great information.

- John

Thanks John, I was wondering if that was a possibility but I just did not know. Ref Mississippi, I'm now in Tennessee BUT the conditions here right now are about the same as they were when we hit Miss a few weeks ago.

When adding " a little" refrigerant , how do you know when to stop?? I know if I'm not careful I could over charge, right?

 

[petersonj]

When adding " a little" refrigerant , how do you know when to stop?? I know if I'm not careful I could over charge, right?

During your testing, did you have the recirculation mode activated? I believe the manual requires this mode to be on. This is especially important on a humid day (almost every day is humid where you are now).

The best practice would be to have an AC shop recover the refrigerant currently in the system and then recharge the system with the proper amount of refrigerant. There should be a sticker under the hood near the radiator on the passenger side that states how many pounds and ounces of refrigerant is required for your specific system.

Otherwise, you have no way to know how much refrigerant is currently in the system and no way to measure how much refrigerant you are adding. All you can do is use the charts as a reference and add a small amount of refrigerant at a time while monitoring your gauges. If the air temperature coming from vent duct starts cooling, then you are benefiting from the added refrigerant. Add only enough to get the job done. You may want to increase the throttle to a high idle (1000 - 1200 rpm) while performing this operation.

Many people add their own refrigerant (I do it myself, as well), but one must assume the risks of overcharging a system if one decides to go this route. Overcharging a system can result in damage to the compressor and poor AC performance. Remember, you are your own warranty station.

- John

 

[Bill Stockard]

The best practice would be to have an AC shop recover the refrigerant currently in the system and then recharge the system with the proper amount of refrigerant. There should be a sticker under the hood near the radiator on the passenger side that states how many pounds and ounces of refrigerant is required for your specific system.


- John

Two years ago, I suspected the refrigerant in our formerly owned '03 3500 was a bit low. I took it to our local dealer and watched the tech evacuate and recharge the system with refrigerant. As I correctly suspected, it was several ounces low and after adding the required amount to the system, it cooled down much quicker after being parked in the sun and the air temp at the outlets was much colder than before. The job ticket was a little less than $100 and well worth it.

Bill

 

[navyjoe]

During your testing, did you have the recirculation mode activated? I believe the manual requires this mode to be on. This is especially important on a humid day (almost every day is humid where you are now).

The best practice would be to have an AC shop recover the refrigerant currently in the system and then recharge the system with the proper amount of refrigerant. There should be a sticker under the hood near the radiator on the passenger side that states how many pounds and ounces of refrigerant is required for your specific system.

Otherwise, you have no way to know how much refrigerant is currently in the system and no way to measure how much refrigerant you are adding. All you can do is use the charts as a reference and add a small amount of refrigerant at a time while monitoring your gauges. If the air temperature coming from vent duct starts cooling, then you are benefiting from the added refrigerant. Add only enough to get the job done. You may want to increase the throttle to a high idle (1000 - 1200 rpm) while performing this operation.

Many people add their own refrigerant (I do it myself, as well), but one must assume the risks of overcharging a system if one decides to go this route. Overcharging a system can result in damage to the compressor and poor AC performance. Remember, you are your own warranty station.

- John

I did have it in recirc with a door open when I checked I just had the compressor replaced about a year ago, (for the second time - long story) so either they did not charge it correctly or I have a leak. I'm going to try adding a little at the time since one cant afford buying their own recovery unit. I do suspect its a little low because the unit started freezing up in Miss. last month. It was so humid you could cut it with a knife and put it in a glass and drink it. As I seem to remember there is a point of when it gets low it goes in to a super-cool phase.

Really appreciate your help!

 

[PWong]

Ambient Air Temperature	21° C (70° F)	27° C (80° F)	32° C (90° F)	38° C (100° F)	43° C (110° F)
Air Temperature at Center Panel Outlet	7° C (45° F)	7° C (45° F)	13° C (55° F)	13° C (55° F)	18° C (64° F)
Compressor Inlet Pressure at Service Port (low Side)	138 to 207 kPa (20 to 30 psi)	172 to 241 kPa (25 to 35 psi)	207 to 276 kPa (30 to 40 psi)	241 to 310 kPa (35 to 45 psi)	276 to 345 kPa (40 to 50 psi)
Compressor Discharge Pressure at Service Port (High Side)	1034 to 1724 kPa (150 to 250 psi)	1379 to 2068 kPa (200 to 300 psi)	1724 to 2413 kPa (250 to 350 psi)	1999 to 2689 kPa (290 to 390 psi)	2413 to 2965 kPa (350 to 430 psi)

This chart was from the A/C Performance Test in the FSM.

The test should be done in the following way:

"Set control to Recirculation mode, temp control to FULL COOL, blower at MAX speed.
Engine at operating temp, hold idle at 1000 rpm.
Doors should be closed and the WINDOWS OPENED.
Note: The clutch may cycle, depending upon the ambient temp and humidity. If the clutch cycles, use the readings obtained before the clutch disengaged."

 

[Motorhead]

I along with pressures, I set the charge by temperature with a digital temperature probe that connects to my Klein Multi-meter. About anything below 38-40 degrees, at least on my 2007, the freeze switch that has a probe into the evaporator will open and disconnect the electromagnetic clutch on the compressor.

 

[sag2]

You can add a little at a time by watching the pressures. Let it run for a while to stabilize, note pressures and add some (are you using 12 ounce cans?) A little at a time. If the can is at ambient when you open the low side valve the low side pressure should go up to 70 or 80. Keep it open for about 10 seconds. Let it stabilize and watch pressures and outlet temp. If it stays about the same on the pressure side you have not added too much. Repeat a couple times and then try it for a few days. If you are hooking up and charging a couple times on different days always purge a small amount out of system and can so you don't introduce air into the system.

 

[navyjoe]

You can add a little at a time by watching the pressures. Let it run for a while to stabilize, note pressures and add some (are you using 12 ounce cans?) A little at a time. If the can is at ambient when you open the low side valve the low side pressure should go up to 70 or 80. Keep it open for about 10 seconds. Let it stabilize and watch pressures and outlet temp. If it stays about the same on the pressure side you have not added too much. Repeat a couple times and then try it for a few days. If you are hooking up and charging a couple times on different days always purge a small amount out of system and can so you don't introduce air into the system.

Good technique, I'll try that! PS I'm using a bulk container - not 12oz cans.

 

[navyjoe]

Well, it was just a little low. About 5, 10 second shots put it back in range. Outlet temp is now about 46F at 89F ambient. Appreciate all of you for your input.

One other thing I did which really helps is putting a fan in front of the condenser coil. That a running it at about 1500 RPM is about like doing 55 down the road.