Air Conditioner Issue

When this first started a couple of days ago, I would turn on the A/C and it would blow cold air for 5 or 6 seconds, then blow hot air, then cold, then stay on hot. I went to the auto parts store and spent $75 on leak sealer and R-134a that the clerk insisted that I need. Of course that day I was driving home and the A/C began to work like a charm and did so for 2 days. Now, even with the fan switched to OFF and the A/C set to its coldest setting there is hot air blowing out of the vents. Fortunately I have not used the sealer and recharger that I purchased yet because this is sounding more like an electrical issue. But then again, I'm a web designer by trade so vehicle diagnosis and repair are certainly not my fortes. Suggestions from anyone what the problem is?

Thanks in advance -
sleepydad

 

probably should take your truck to a specialist on a/c and get them to diagnose your a/c. could be anything

 

Okay I've been observing the behavior for about a week now, and here's what I've noticed.

The A/C works great for exactly 1/2 hour then begins to blow out intensely hot air. I went to the auto parts store and purchased some leak sealer and R-134a. When I put the gauge on the low pressure intake and the A/C was blowing cold air, I got a reading of 30psi. I let the truck run until the A/C started blowing hot air and noticed that the pressure dropped immediately to 20psi. I sprayed in the sealer and recharged the R-134a to 40psi using the manufacturer suggestion assuming the outside temp was 75 degrees. I've run it twice since then, and the same thing ... 1/2 hour glorious cold air then a sauna. I noticed today that when I shut the engine down for about ten minutes then restarted, the A/C began working properly again . The counter person at the parts store all but ruled out replacing the A/C unit because, according to him, I'd be hearing some noise if the entire unit was bad (There's no unusual noise). He suggested perhaps a relay, but didn't sound terrible convincing.

Does this scenario ring any bells with anyone? I'm off to Google A/C relays right now.

Thanks all -

 

sounds like the AC is cutting out on either High or Low pressure. Is there a cabin filter (behind glove box)? has it been changed? is the evaporator dirty? You can run some water through the condenser (which is behind the radiator, but smaller), maybe that got dirty if you went mudding or something. Does the compressor keep turning (spins when the clutch is engaged) when it stops blowing cold? My guess is no. If it's electrical, it might be good to find a technician.

 

^ The 1gens do not come equipped with a Cabin Filter. I'd recommend you check the Blower behind the glove box OR the resistor that is on the blower. Both are common to go out on these models.

 

Sound like to me you have some blockage in the a/c line. I know very little about ac systems but I have seen this problem before. There is an orifice(cant think of the name) that gradually becomes blocked the longer the ac runs. When you shut it off it recovers some, then running it again starts it over again.
I dont know how to repair it either. Wish I could help more.

 

Does anyone have any info on how to clear blockages?

Last August my AC quit just as the OP describes. I shot a can of coolant with no results. Took it to a shop to have it professionally done. He said the gauges on the machine showed a blockage and he had to pressure test each piece in the system. I opted to sweat balls thru September.

The compressor and fan still run. They just blow warm/hot air no matter the AC or coolness setting, through the blow isn't 100 percent strong.

Any thoughts on how to troubleshoot are appreciated. Thanks.

 

Sounds like a bad txv
What is you're high pressure side reading ?

 

Not 100 percent. Had it done in August, but I remember one was too high and the other zero.

 

I had a decrease in cold air blowing for some time and an AC guy showed the high side being way too high but as time went on it got to the point of no cooling and a hissing from behind the dash about 15 seconds after turning the AC on.

In the end to take no chances nor trusting the previous owner I replaced everything but three hard lines. Someone in the past replaced the condenser, receiver/dryer, and compressor with cheap crap. Now everything is back to Denso except for the two hoses and it blows colder than ever and better than many other cars I have had.

Sadly it is not a cheap or quick job but luckily I did all the work myself except for the refrigerant part of the job but that was at a huge discount.

I do not know where exactly the issue was but didn't want to take a chance trying to piecemeal it and costing me more time and money.

 

Zero is quite difficult to reach. I've only seen that when both sides were zero and the system had leaked all the way down to atmospheric pressure over time. The pressures do tell you a lot. Undercharged, overcharged, orifice tube blockage, and sometimes after a compressor self-destructs, a restriction (pretty commonly in the orifice tube but also have had it happen in the condensor or evaporator, whereever crap sticks.

About the zero pressure: If you have any sort of a freon charge, a modern compressor will "suck out" at the 20-30 PSIG range. To have high on one side and zero on the other, you would have to have (a) a gorilla of a compressor and (b) a total blockage somewhere. Otherwise some of that high side pressure would always be leaking to the low side through the orifice tube (or expansion valve, which ever you have).

 

You are probably talking about moisture in the system. It will form ice crystals at the orifice tube since it is so cold where the pressure drops and the freon starts to flash to a gas. The ice will block freon flow, things warm up, the ice melts, the thing blows cold, the water freezes again, over and over. For ice, about all you can do is recover the existing freon, pull a hard vacuum to boil off all the moisture, and re-charge. It's common to also replace the receiver-dryer before you do this since the dryer is probably "done".

Dryer is not that expensive. An evacuation/recharge might run 200 bucks or so with todays highly inflated R134a prices.

However, that hot/cold/hot/cold can be caused by other things, even as simple as a bad cycling switch. Some use a Schrader valve and can be removed without discharging the system. Some not.

 

Although someone revived this from 2011, I currently have the same issue.
On the climate control it's on the coldest setting- when everything is off warmish air manages to seep in, when on low the air is warm, on high it's like it should be on low or the 2nd setting.
Dealership told me it was the ac compressor. $800 fix iirc

 

This sounds like a restriction. 20psig is WAY down there and would really be too low for an auto A/C, it would tend to freeze the moisture from the air as it flows through the evaporator. Does your vehicle use an orifice tube or a tx valve? If the little copper pressure/temp sensor gets too cold, the tx can shut freon flow down, which would produce that whopping low pressure...

Moisture CAN do this, but the 1/2 hour interval seems strange for moisture. Of course it sounds strange for any rational explanation.

 

Where's Keakar!? He should be around shortly. He's an A/C guy by trade.

 

Maybe I'm wrong. There was a language barrier with the mechanic, but I know he said too high on one side and nothing on the other—maybe nothing wasn't exactly zero?

I'm going to take it to the dealership for the tire carrier recall this weekend. I'll try to get them to hook it up and give me numbers.

 

you rang?

ok here is whats going on as far as I can judge without being there.

you have too much moisture in the system, what happens is the moisture forms tiny ice crystals in the metering device as it circulates through the system and over time enough ice crystals form to start restricting the flow and the pressures on the larger "return" line starts dropping until the low pressure switch shuts the compressor off to keep it from burning up. the system blows hot air because the compressor cant run until the ice crystals melt and the system equalizes pressures again and you are back to normal.

what you need to do is replace the receiver drier on the a/c condenser by the radiator (not easy to get to) then do a good full vacuum on the system for not less then 30 minutes to remove all remaining moisture in the system, then refill with Freon.

now the moisture is in the system for a reason so that means its leaking somewhere so look for oily film around fittings and connections that are a sign those O-rings need replacing. replace any of these O-rings before vacuuming and refilling the system and you will be good to go.

 

If it's ice crystals, wouldn't it have worked on a warm day— until the AC got cold and built them up?

Since it died, it's never blown cold air again. The OP did say his worked for about a 1/2 hour at the start of the day, then quit, but mine has been out out since it went down. I should have been clearer.

 

no, Freon creates its own temperatures, the outside temperature doesn't really have anything to do with the internal systems unless your running it in winter time.

the way an air conditioning or refrigeration system works is the compressor takes the Freon from the low pressure line and compresses the Freon under high pressure, then as it cools (still under high pressure) going through the condenser, it does just that and condenses into a liquid which then goes through the lines to the metering device. then the Freon goes from high pressure liquid through the metering device at the pressure suddenly drops dramatically causing it to instantly flash into a vapor and this flashing evaporates the liquid into a gas form and that vaporization causes a huge temperature drop which turns the evaporator coil very cold and if there is any in the system, it instantly freezes water or moisture into ice. the cold temperatures on the low pressure line is also what is used to keep the compressor cool and it carries a small amount of oil with it that circulates through the system to keep things lubricated so seals don't dry out.

it wouldn't matter if it was in a 200 degree oven at the time, it would still form ice crystals.

 

Thanks man. I'm gonna start reading up on swapping out that drier. Thanks again.