Ac Question

[grose67]

I have a 98 GMC Z71 Extended cab 4X4. Has anyone heard of the AC freezing up similar to what sometimes happens to home AC units? After I run my AC for 30 to 45 minutes, the airflow is all but cut off. I checked the motor that changes the airflow from defrost to dash or floor. It is in the correct location. I am seeing condensation forming on the housing where the air passes through the "chiller" coils.

[bill190]

Check that your high/low refrigerant pressures are factory spec. And while doing that, use a multimeter to check the low pressure cut-off switch to be sure it is operating as it should.

 

You would need a set of gauges, multimeter, and GM factory service manual set.

[bewagner68]

I have experienced this same sort of thing with my "new to me" 2007 Yukon when running the AC. We can run the AC for about 20 minutes before it freezes. Took it to our mechanic who changed 1 switch and it did not fix the problem. He ordered a second switch (AC Low Pressure sensor) but when he put it on the AC unit, the unit did not work at all so we are waiting for another one of these switches because he thinks we may have gotten a defective switch. Does anyone have any ideas?

Thanks.

 

04/29/2011 I got my vehicle back yesterday after having the AC low pressure sensor changed and the AC unit is still freezing up. The AC is blowing cold air however, even when the unit is covered in ice. Mechanic is not leaning towards coolant level because when the AC is blowing, it is putting out cold air. The next step he is telling me is to pull the system down to check a screen filter in the oriface tubing. Could you please offer any other suggestions? This is very frustrating.

[asc08]

What exactly is freezing up? If it is the evaporator coil located in the dash, I cant imagine that you would be getting any airflow. If there is frost on the components under the hood, it may be normal operation in high humidity conditions. As was posted before, check to make sure the refrigerant levels are correct, by using a set of gauges. The lines coming off the compressor to the condenser, and from the condenser to the evaporator should be warm or hot. The line coming from the evaporator to the condenser should be cold (anything on this cold line may be frosted or covered with condensation).

[bewagner68]

What exactly is freezing up? If it is the evaporator coil located in the dash, I cant imagine that you would be getting any airflow. If there is frost on the components under the hood, it may be normal operation in high humidity conditions. As was posted before, check to make sure the refrigerant levels are correct, by using a set of gauges. The lines coming off the compressor to the condenser, and from the condenser to the evaporator should be warm or hot. The line coming from the evaporator to the condenser should be cold (anything on this cold line may be frosted or covered with condensation).

 

The accumulator is covered in white ice or frost........the connectors up to the rubber hose and the metal line from the refrigerant valve to the accumulator are also covered. 2 weeks ago, we did experience no air flow, but haven't since. Everyone that I have described this scenario to (and there have been a few) have all said the same thing..."coolant level is low". The mechanic DID NOT check levels because he based his diagnostic on feel, which I know is not the right thing to do, however we are now going to drain the system completely, record what is recovered so we will know what was in there and then refill to factory specs........We live in Virginia and have not yet hit high humidity temperatures, however it was raining this morning and I needed the defrost only. I ran it at 74 degrees F; when I got to work I checked under the hood; the accumulator and tubes were iced over..........

[asc08]

As you will see if you spend much time on this forum, throwing parts at a problem is discouraged. Before the mechanic who installed the pressure switch does any more work on the AC, take it to someone who has the tools and experience to fix it.

 

I agree with those who suggest low charge.

 

If it is low charge, have a leak check done. This is sometimes done with soapy water, but the better method is a dye check, where they put dye in the system, run it, and then look for leaks with a special light and special goggles.

[Jsdirt]

Low charge, +1 .

 

... and another cause of freeze up that will eventually destroy the compressor due to oil starvation (slugging) is the LPCO .... or Low Pressure Cut Off switch. Low side shouldn't go much below 25 psi or so. If it's getting down in the teens & the compressor runs constantly without kicking off, bad news - replace that switch. That's an easy one. Simply unscrew it out of the accumulator & screw in the new one. No recharge needed, unless it was low to begin with.

 

If the compressor gets real noisy it's too late.

[bewagner68]

Low charge, +1 .

 

... and another cause of freeze up that will eventually destroy the compressor due to oil starvation (slugging) is the LPCO .... or Low Pressure Cut Off switch. Low side shouldn't go much below 25 psi or so. If it's getting down in the teens & the compressor runs constantly without kicking off, bad news - replace that switch. That's an easy one. Simply unscrew it out of the accumulator & screw in the new one. No recharge needed, unless it was low to begin with.

 

If the compressor gets real noisy it's too late.

 

Is the LPCO that same as the Low Pressure sensor? Two switches on the accumulator have already been replaced. No sound from compressor. The reason we replaced the sensor is because the auto tech said that the unit wasn't cutting itself off when it reached temp. I don't believe that is happening anymore since we changed the switch. Just that darned icing and frosting over of the accumulator. And it doesn't happen all the time.........really wierd.

 

The mechanic did say that they did look for leaks, but did not see anything and that the system was loaded up with dye. Said he would have felt better about it all IF he did find a pinhole....................????????????

[Jsdirt]

Sounds like just low charge. If your evacuating it anyway, just charge to the correct weight & it should be good to go. Finding & fixing a leak would be better though ....

[bewagner68]

Turns out my problem was more than low charge, though that was also a problem.......The A/C control module had to be replaced............Now my A/C is working like a charm......... , but it did cost me a pretty penny. Though, I think that could have been worse too. I am very thankful for the expert help I have received..........thanks to all of you!

[Jsdirt]

Yeah, gotta HATE electronics these days - par for the course.

 

Glad you got it sorted out!

[bewagner68]

Yeah, gotta HATE electronics these days - par for the course.

 

Glad you got it sorted out!

 

Me too........took the dealership 2 days to do it though.......they tried everything to figure it out........from driving trucks on the lot like mine to see if it was infact something normal...........to goodness knows what! I would have been happy with the good old twisty control........Oh well.........should be ready for the summer now!

Thanks for all of your help!

[Jsdirt]

You got it!