A/C Freezing up?

[old_master]

Low side pressure is controlled by the cycling switch. It turns the compressor ON when low side pressure is above 42psi. The cycling switch shuts OFF the compressor when pressure drops to 22psi. When the AC is on, the pressure should always be between 22psi and 42psi, if it's not, there's a problem. Using the AC in the recirc position will produce less condensation from the drain, and colder register temps also. When the system is not in the recirc mode, outside air, and humidity, is continuously passing across the evaporator, thus creating more condensation and higher register temps. The only time you shouldn't use recirc is when some one in the vehicle is smoking... it makes the ductwork stink.

If low side pressure is at 65psi while the compressor is running, there's a problem. Several things can cause low side pressure to be too high: restricted low side line from the accumulator to the compressor, torn or missing fixed orfice tube, cycling switch out of calibration, but the most common reason is the system is overcharged. High ambient temperature will cause low side pressure to increase and the clutch might not cycle, but pressure should always remain between 22psi and 42psi.

[rjeffery]

I checked the pressure with the doors and windows closed, recirc on & blower on max, as suggested. Pressure was 35 psi. This seems to be within spec. If you still believe system to be overcharged, maybe I should have some refrigerant removed?
BlackBerry8310/4.5.0.110 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102

[j cAT]

Originally Posted by rjeffery

I checked the pressure with the doors and windows closed, recirc on & blower on max, as suggested. Pressure was 35 psi. This seems to be within spec. If you still believe system to be overcharged, maybe I should have some refrigerant removed?
BlackBerry8310/4.5.0.110 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102

my opinion with this ,since I have the same system , " this is normal operation". 35 psi with the vehicle closed to the outside air is quite good. the problem I suspect is leaving the ac in the rec mode too long. also make sure the evap coils are clean behind the new air filters you just installed , and the drain tube is clear for the water condensated to drain . when operating with the high humidity there should be a steady flow of water coming out ...inserting a small rubber hose / rubber vacuum line into this will loosen any blockage in most cases..

[saturntech]

sounds like rstricted txv valve, its where the a/c lines runs through the firewall, If its plugged your going to have freezing.

[old_master]

Originally Posted by rjeffery

I checked the pressure with the doors and windows closed, recirc on & blower on max, as suggested. Pressure was 35 psi. This seems to be within spec. If you still believe system to be overcharged, maybe I should have some refrigerant removed?
BlackBerry8310/4.5.0.110 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102

You're right, it is within spec (22psi to 42psi) however, as mentioned, it should cycle unless relative humidity and/or ambient temperature are high. If the system is over or under charged, it's impossible to diagnose it correctly. With clutch cycling systems, the only way to be sure how much refrigerant is in the system, is drain, evacuate and recharge it with the proper amount.

[old_master]

Originally Posted by saturntech

sounds like rstricted txv valve, its where the a/c lines runs through the firewall, If its plugged your going to have freezing.

This is a clutch cycling system, it's not equipped with a thermal expansion valve. The system uses a fixed orfice tube and a cycling switch to control evap pressure. Good idea though, if the orfice tube is restricted, evap pressure will drop and cause ice up, but at the same time, high side pressure will go sky high and there's no mention of that.

[rjeffery]

So I've replaced the air filters, cleaned the evap coils, unclogged the drain line, and made sure the pressures are within spec. I haven't been on a road trip in a while, so I haven't been able to test it. Seems like there is not an obvious solution short of draining and refilling the freeon. If it's not fixed, it's something I'll live with. Thanks for all of your help in diagnosing the problem.
BlackBerry8310/4.5.0.110 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102

[j cAT]

Originally Posted by rjeffery

So I've replaced the air filters, cleaned the evap coils, unclogged the drain line, and made sure the pressures are within spec. I haven't been on a road trip in a while, so I haven't been able to test it. Seems like there is not an obvious solution short of draining and refilling the freeon. If it's not fixed, it's something I'll live with. Thanks for all of your help in diagnosing the problem.
BlackBerry8310/4.5.0.110 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102

I suggested you not use the rec mode . did you run the ac in fresh air only , to see if it froze up ?

[rjeffery]

Yes, it freezes in fresh air mode. I only really use recirc mode to cool it down quickly, then I switch to fresh air.
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[j cAT]

Originally Posted by rjeffery

Yes, it freezes in fresh air mode. I only really use recirc mode to cool it down quickly, then I switch to fresh air.
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having worked on many types of air conditioners over the years your problem with your pressures and cooling performance has always been an air flow problem thru the evaporator coils in the air ducting being restricted...I have seen on the 20 ton units lots of ice with this type of issue of air flow being low or none.