A/C Issues with my Pacifica


#1

Hello all…hoping someone can give me some insight and perhaps a direction to move in to resolve a stubborn issue with my Pacifica. I apologize in advance for the length, but giving all this info may help.

Its a 2004, purchased within months after introduction. I have about 109,000 miles on it and it really has been a great vehicle for my family.

The problem I’m trying to resolve is with the A/C (and perhaps related to the heater as well). It first surfaced almost a year ago when transporting our daughter back to college…a long drive in early September from NJ to GA. About two hours into the trip we felt the temperature rising in the cabin to somewhat uncomfortable levels. It was a hot day, but we then realized that no cold air was coming from the dash vents. Matter of fact, almost no air was moving through the vents.

We pulled off the interstate at a local mechanic to ask him to take a quick look and see if there was anything wrong. Knowing we still had a good 10 hours of driving into hot steamy GA, being without A/C was not going to be good. This mechanic said it would be about an hour, so we went for lunch. When we returned, he pulled the car around and told us NOTHING was wrong…and sure enough ice cold air was now blowing through the vents.

We continued our trip. And about 90 minutes later, the air got warmer…and again ultimately stopped coming through the vents. We discovered that if we shut the A/C off completely to let it ‘rest’ for 45-60 minutes, we could get cold air back for another hour, so we continued the rest of the trip alternating between hot and cold and took it in when we returned to our regular mechanic.

He inspected and found nothing seemed to be wrong. Said they couldn’t duplicate it. As the weather was getting cooler and no A/C was needed, we kind of put it on the back burner.

Around December, we noticed a similar problem develop with the heat. After 60-90 minutes, the warm air stopped blowing into the cabin. We could HEAR the blower motor running, but the airflow was not there. Our feet were getting COLD on long drives. The heat would work fine around town during short trips, but anything more than 60-90 minutes and it would get cold.

Something went wonky with the resistor and blower, so we had the resistor changed. Also had the thermostat replaced, thinking that might be the issue. We never really drove it a long distance after that so don’t really know if the issue is resolved.

We discovered around Easter that the A/C issue remained and were determined to get it fixed before returning to GA in June to get our daughter. I opted to take it to a Chrysler dealer with the belief that they would have a better understanding of the system (over my mechanic). I asked them to PLEASE duplicate the problem, even if they had to burn a tank of gas to do it.

After a day at the shop, they called me and claimed they had duplicated the problem and discovered that there was ‘rodent debris’ in the intake area and it was blocking the airflow, probably causing things to freeze up. They cleaned and disinfected everything out, changed the cabin air filter and pronounced it fixed.

We left for Georgia. It wasn’t fixed. Sure enough, 90 minutes in, the air got warm and ultimately stopped blowing into the cabin (but we can hear the blower working). We shut the A/C off but left the blower on and in an amazing twist, suddenly there was a RUSH of cold air coming in, for about 15 minutes. As it got warm again, we’d put the A/C back on and could get nice cold air for another 90 minutes. We cycled like this all the way to GA and back.

My logic tells me SOMETHING is freezing up and blocking the airflow, and then when we shut the A/C off and just let the blower work the ‘ice’ starts melting and thus clearing the way for the air to flow into the cabin again. Its cold because the air is moving over something icy, and then once it melts the air gets warm again. Since the blockage is now melted, the A/C can work again until it freezes up and blocks the airflow.

But what is it REALLY? How do I explain what repair I need, or even get someone to diagnose this? Having had to to two different places and gotten nowhere, I am at a loss as to what to do now.

I also wonder if the A/C issue isn’t somehow related to the heat issue.

If you made it this far, thank you so much…and if you have any advice to offer even better!


#2

The air conditioning problem may be caused by the evaporator freezing up. This would reduce the air flow. Shutting off the air conditioning compressor would allow the ice to melt and then, when the compressor is turned back on, the system will again function normally. You gave a hint that this is what is happening when you said that leaving the blower on but turning the A/C off suddenly gave a rush of cold air. This was the ice melting.
The icing is caused by the humidity in the air. As you proceed further south to Georgia the air becomes more humid. Your method of turning the A/C off for a few minutes and then turning it back on is a solution for the problem.
I don’t know if there is a sensor that will turn off the A/C compressor automatically as the ice builds up and then turn it on again. I had the same problem with a room air conditioner on humid days. The coils would ice over and I would turn it off for a few minutes to melt the ice. I could pull the front off the air conditioner and see the ice. When the ice melted away, I would restart the A/C. I found that if I didn’t open the vent on the room air conditioner to bring in outside air, it was less likely to ice over. Perhaps running your A/C in recirculate mode might help.


#3

Incidentally, in the old days, we used to have to manually defrost a refrigerator. The humidity in the air would allow the ice to form on the coils in the freezer. The refrigerator had to be defrosted more often in the summer because of the higher humidity. Most refrigerators today have an automatic defrosting mechanism that shuts off the compressor, turns on some heaters to melt the ice and the water drips down into a pan on the condenser coils. The compressor then comes back on. The heat from the condenser evaporates the water. Your car air conditioning works on the same principle as the refrigerator moving the heat from the cabin to the condenser coils in front of the radiator. The humidity in the air condenses on the evaporator coil much like the humidity in the air condenses and freezes on the outside of a cold mug of beer in the summertime


#4

I’m not sure about automotive applications, but in your home A/C, this is indicative of low refrigerant…at least, it used to be.

Chase


#5

Chase–

You may be right about the unit being low on refrigerant. I would have thought that the technician would have hooked up the gauges to see on the OP’s Pacifica, just as the first thing my doctor does when I go for a checkup is to check my blood pressure. This may have been the problem with my room air conditioner. It was a used unit that I bought for our apartment when I was a graduate student. I didn’t pay much for it and as long as I could make it cool, I lived with it.


#6

It was happening at my house, and I was perplexed. I’m NOT an A/C guy, but I always watch and ask a lot of questions when anyone’s doing something to my house (I think A/C is about the only thing I don’t do). The weather was pretty warm, and I came home to a really hot house. Checked to make sure the system was running, and the outside unit was frozen pretty solid. A hose worked for the immediate meltdown, but it started freezing right back up, so I made the phone call. After watching and asking questions, it was low a couple pounds. They claimed no leak, and I went on a contract with them…they were relatively cheap, friendly and quick. No problems since then.

Not an important story (nor even really relevant), but it’s one of those things you remember.


#7

This is strange that your outside unit would be frozen solid. When you are in the A/C mode, the outside unit is the condenser and it is supposed to be getting rid of the heat from the house. If you have a heat pump, in the winter, the outside unit acts as the evaporator and removes heat from the outside air and the indoor unit then serves as the condenser. For some reason, it sounds as though you had a reverse flow of the refrigerant.
I’ll still stick with my original diagnosis of the OP’s problem that the humidity in the air is causing the evaporator to freeze over.


#8

My home A/C compressor did the same thing with low freon. The coils are supposed to get rid of the heat, but instead they froze solid. Called the ac guy and he added freon and I was good for another year. Then it died again and I replaced the unit.


#9

As Triedag responded, the evaporator is collecting ice until all air flow is blocked. When the A/C is turned off, the ice melts and you can get air to go through the evaporator again.

The expansion valve is sandwitched between the evaporator and the liquid and suction lines. This valve controls the amount of liquid R-134a let into the evaporator. It monitors the pressure and temperature of the suction line gas. If this valve is defective it will allow the evaporator temperature to drop below freezing and ice will form on the fins through which the cabin airflow is routed.

The A/C service technician should have noted this problem from an excessively low suction pressure even with maximum cooling being demanded.

There is also an Evaporator Temperature Sensor that sends a signel to the Auto Temperature Control. However, the ATC does not appear to interface with the PCM to control the compressor clutch relay so I don’t know why the ATC needs the ETS sensor data.

HTH