A/C Freezing up?

Hey guys, after running my A/C for about an hour (at highway speeds), it stops blowing cold and the air volume decreases. If I turn the A/C off for a few mins, then back on, it will blow cold again. I'm thinking maybe something is freezing up. What do y'all think?
BlackBerry8310/4.5.0.110 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102

System could be overcharged and the pressure cycling switch is not working properly.

Any recent work on the AC?

//2000CAYukon

Hey guys, after running my A/C for about an hour (at highway speeds), it stops blowing cold and the air volume decreases. If I turn the A/C off for a few mins, then back on, it will blow cold again. I'm thinking maybe something is freezing up. What do y'all think?
BlackBerry8310/4.5.0.110 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102

your vehicle should have a air filter in the air box . remove this filter , if very dirty this is why.no air flow the evap will freeze into a solid ICE cube.

always replace these every year , may need to do it more often in dusty areas..these are 2 filters side by side. cloth material . auto stores have them ,,,if you do not replace them and operate with no filter the evap/air dampers get damaged.

Yeah, I haven't replaced those in a few years. I'll give that a shot and see if it works. I'll let you know how it goes.
BlackBerry8310/4.5.0.110 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102

So I replaced the cabin air filters, and the A/C is still freezing up. I had a 4 hour drive today and the A/C froze up every 30 mins or so. When I stopped, the cylindrical deal on the firewall (condenser?) had ice on the line going to the compressor and on the line coming off the top. Someone told me that it may be a bad switch that cycles the compressor on and off, so the compressor is not cycling off and the system is freezing up. Any input is appreciated.
BlackBerry8310/4.5.0.110 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102

So I replaced the cabin air filters, and the A/C is still freezing up. I had a 4 hour drive today and the A/C froze up every 30 mins or so. When I stopped, the cylindrical deal on the firewall (condenser?) had ice on the line going to the compressor and on the line coming off the top. Someone told me that it may be a bad switch that cycles the compressor on and off, so the compressor is not cycling off and the system is freezing up. Any input is appreciated.
BlackBerry8310/4.5.0.110 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102

then I would drop the blower motor and inspect for the fan to be clean and the air intake hole not restricted...insuffcient air flow will do this. you must have a very 70deg plus dew point...

So why don't you replace the cycling switch? or at least test it by watching low side pressure with your gages (or a borrowed set). Put blower motor on lowest setting and watch low side pressure- if pressure goes below 20 psi or so-- your switch is not doing its job. The switch would be the first place I would look when dealing with evap freeze-up.

Thanks for the suggestion. Where is the switch located, and do you know the part number? I did some google searches but didn't have much luck finding the part.
BlackBerry8310/4.5.0.110 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102

Thanks for the suggestion. Where is the switch located, and do you know the part number? I did some google searches but didn't have much luck finding the part.
BlackBerry8310/4.5.0.110 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102

where you live with the temps well into the 90deg f area I doubt this low pressure switch would open since the pressure if charged properly will not drop below 15psi on the charging port. using a pressure guage measure the pressure to see if the pressure drops below the 15psi and see if the compressor clutch cuts out. if the switch does not open when the pressure is below 15psi then it is defective ....normally however this switch opens when it fails and you get no cooling...


evap freeze ups are from lack of air flow with very high humidity or a low charge condition that can create a partial icing condition of the evap coils...

report back what pressure you have on the low side charge port. with windows open and fan on max. also the air temp of the area..

First thing I'd check is the condensate drain. If it's clogged, condensed humidity will accumulate on the evaporator. Refrigerant going through the evaporator will freeze the condensation on the outside of the evaporator causing it to ice up. If this happens, air flow out of the registers will decrease, and temperature will increase. Let it sit and thaw out...works fine until it ices up again. This scenario is very common in high humidity situations. Setting the AC mode switch on recirculate will reduce the tendency to ice up. The drain is located directly below the evaporator housing, accessible from under the vehicle... 1/2" diameter rubber hose pointing straight down, maybe 2" long. Stick a drinking straw inside and wiggle it around. Keep your face away, you might get an unexpected shower! Don't stick anything metal in the drain, you'll likely damage the evaporator.

Ok, with doors open and blower on low, low side psi is 35. With blower on high, psi is 65, which seems high. Temp outside was 85 deg when psi was measured. Freezing tends to occur when outside temp is over 100.

I also cleaned the drain tube. If I run the A/C on recirc for even a short while, it begins to smell musty. If I run it on recirc for a long while, it will drain water onto the passenger side carpet.
BlackBerry8310/4.5.0.110 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102

The drain is clogged, that's why it drips on the carpet.

To test pressures, mode switch on MAX AC (recirc), blower on high speed, windows and doors closed, engine at 1,500 RPM, and at operating temp, good air flow across condenser, (might require a fan blowing at it if it's above 80F ambient): The compressor should turn off when low side is at 22psi and turn back on at 42psi, cycling continuously. The average psi should be at, or just above 32 psi. R134a is approximately the same psi as its degrees are in Farenheit. For example, at 32 psi, evaporator temperature is approximately 32F. If it's below 32 the evaporator will ice up, if it's above 32 it will not cool sufficiently. High side pressure varies greatly depending on ambient temp, humidity, amount of refrigerant charge, air flow across condenser, and the overall condition of the AC system components. Just as the compressor turns off, pressure should be in the ball park of 250psi. Keep in mind that if ambient temp and/or humidity is high, the clutch may not cycle, and register temperature will increase. Rule of thumb with R134a systems that are in good condition, is register temperature will be 20 degrees lower than ambient temperature. If temp drop is more, consider it a bonus.

Does your drain tube have a rubber elbow on it--- air pressure will back up on it while driving and cause the flooded carpet, if no rubber elbow-- seen it on B cars when factory forgot to install drain tube elbows......

This (flooded carpet with drain tube elbow missing) only happens when driving non-stop for 30+ minutes on highway-- so when does your carpet get flooded, city driving, or highway non-stop driving?

My drain has the rubber elbow. Carpet gets wet when driving on highway, but has not happened in a while (maybe b/c I don't use recirc on the highway).

Do my psi readings seem high? From what I have read, low side should be less than 45. Mine is 65.
BlackBerry8310/4.5.0.110 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102

Ok, with doors open and blower on low, low side psi is 35. With blower on high, psi is 65, which seems high. Temp outside was 85 deg when psi was measured. Freezing tends to occur when outside temp is over 100.

I also cleaned the drain tube. If I run the A/C on recirc for even a short while, it begins to smell musty. If I run it on recirc for a long while, it will drain water onto the passenger side carpet.
BlackBerry8310/4.5.0.110 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102

the pressures seem normal. as I expected where you live this low pressure switch will never cut out with the high temps you have NOW ! you should only operate in the recycle mode with these vehicles to get rapid cool down. if you keep it on too long freezing of the coils can happen with the extreme high humidity. so try this with outside air and you should not get the coils to freeze up...when the coils freeze driping on the interior is gonna happen this is condensation of the exterior of the air box which has ice in it....much like a drink with ice cubes on a hot humid day..


ya 65 psi is a little high but 90 plus heat will , with a proper charge , can generate this pressure...especially when the vehicle is stopped..the condenser has not much AIR flow ..


still it is possible the evap coil did get dirty and you have some blockage . removal of the filters and try to see/clean with a small brush the evap coil just behind the filter[s] mounting hole..

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.

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

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..

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

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.

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.

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

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 ?

Yes, it freezes in fresh air mode. I only really use recirc mode to cool it down quickly, then I switch to fresh air.
Mozilla/5.0 (iPod; U; CPU iPhone OS 4_0 like Mac OS X; en-us) AppleWebKit/532.9 (KHTML, like Gecko) Version/4.0.5 Mobile/8A293 Safari/6531.22.7

Yes, it freezes in fresh air mode. I only really use recirc mode to cool it down quickly, then I switch to fresh air.
Mozilla/5.0 (iPod; U; CPU iPhone OS 4_0 like Mac OS X; en-us) AppleWebKit/532.9 (KHTML, like Gecko) Version/4.0.5 Mobile/8A293 Safari/6531.22.7

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.