Intermittent AC Cooling

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First of all, would you please not tell me to take my car to an AC expert. Pretty please? I am here to try and get it figured out with your help first. If that proves to be unsuccessful, I am most definitely going to an AC shop.

Here's the scenario. 2006 Toyota Highlander that is not mine so I don't drive it often. While riding the other day, I noticed the AC air temp coming from the vents was not as cold as normal. Got one of those AC/Pro gauge hoses from Walmart that you screw on top of a can of 134. I then attached it to the low pressure side and noticed the pointer went to the low side of the green at the left red mark on the dial. Doors open, AC on MAX. engine at operating temp. We added 134 and checked. Added and checked. Air got noticeably colder to the touch at the vents. Rotated can from 12 to 3 as we added. The pointer barely rose at all. Maybe went up to about 1/3 way into the green between the red V.

All of a sudden the AC fan started going on and off, on and off, on and off every few seconds. Sounds changed. Pointer still isn't halfway between the red V in the green area. Decided to add another can. Hooked it up and checked pressure and now it is in the red. Too FULL before any 134 was added. We did not add any 134 from the second can. AC Fan still cycling like a madman. Unhooked everything. All of a sudden the AC fan started running like I thought it should. No quickly starting and stopping. We decided to recheck the AC pressure and it was back in the green about 1/3 way up.

What happened? We went for a drive. Air at vent just cool. About a mile later the air at vent gets ice cold. Stays cold for about 15 seconds and then gets cool again. Did we blow something?
 
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Using A/C Pro...
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Don't ever use that junk, or ANY DIY recharge can. You need a set of real manifold gauges (as well as other tools) to properly diagnose an AC system, and the only way to know for sure if you have the proper amount of refrigerant is to evacuate the system and recharge it by weight.

The total refrigerant capacity for that car is probably around 20 oz (couldn't find an exact spec in my brief search). Given that you've added 2 whole cans, which are at least 12 oz each, on top of whatever amount of refrigerant was already in there, you are WAAY overcharged. You are in way over your head. Take the car to a pro, and hope they don't give you grief over using that junk refrigerant with leak sealer and other junk additives that may screw up their AC machine.
 
I'm dealing with a very similar scenario with my 2008 Subaru right now, so I'm in for replies. Not an A/C guy whatsoever. Car has been fine for the last 2 years I owned it and air just started getting warm so I hooked up a gauge and put a can of R134 in it. Air got colder but still isn't as cool as before and does not seem to be cooling much at all when idling.
 
I only used the AC Pro Gauge and a regular can of 134. I only added 1 can. Well, actually it wasn't one can based on what I saw when we detached that first can. I should say I added 10 oz.

The AC system in a 06 Highlander holds 23 oz R134a and 4.5 oz PAG-46

I had only attached the second can because the gauge had barely moved from the adding of the first can. I didn't add a single squirt. Notice, I have modified OP to stress only one can was added.

Hey, I watched a YouTube video. Ain't I qualified?
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I'm wondering if that "[censored]" gauge gave me false readings and I overfilled it?
 
My goodness. I used an AC PRO gauge....

And a can of CarQuest R134A...

I think I am only "qualified" because I apparently haven't done it correctly yet.
 
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On an automotive R-134A system , a VERY Rough rule of thumb is to shoot for around 35 psi .

But , yes , better to charge by weight of refrigerant in the system .

Refrigeration / A/C work via temperature & pressure . Too much refrigerant is not better .

Make sure the condenser coil is not full of bugs .

If you have a cabin air filter , check it . Check the belt driving the compressor . You already said the radiator fans are working , at least part of the time .
 
Originally Posted By: WyrTwister
On an automotive R-134A system , a VERY Rough rule of thumb is to shoot for around 35 psi .

But , yes , better to charge by weight of refrigerant in the system .

Refrigeration / A/C work via temperature & pressure . Too much refrigerant is not better .

Make sure the condenser coil is not full of bugs .

If you have a cabin air filter , check it . Check the belt driving the compressor . You already said the radiator fans are working , at least part of the time .


Excellent point on cabin filter. I checked it last night and it was full of craaapy stuff. I'll call my son and see if it is working better today.

Thank you. Will follow your instructions this weekend.
 
I should have said 35 psi low side / suction pressure .

Sorry for the senior moment . :-(

There are other things , but I would check those first . Not a bad idea to set a box fan in front of the radiator , blowing at the condenser coil .

You may want to run the engine at normal highway speed , not idle .
 
I knew what you meant. I have some "real" gauges that I can check it tonight.
 
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Could the problem be with the automated climate control, and not with the underhood a/c system?

I'm having a similar problem with my 02 Volvo. When it's operating properly it cools fine.
 
Originally Posted By: Kestas
Could the problem be with the automated climate control, and not with the underhood a/c system?

I'm having a similar problem with my 02 Volvo. When it's operating properly it cools fine.


It may be.
 
Possible . I have read od an evaporator temp sensor going bad .

But , I would do the easy checks first . Hate under the dash work ! :-(


PS You may have a control valve that regulates hot coolant circulating through the heater coil .

That could be messing up , also .

Also blend doors / actuators messing up .
 
Originally Posted By: Kestas
Could the problem be with the automated climate control, and not with the underhood a/c system?

I'm having a similar problem with my 02 Volvo. When it's operating properly it cools fine.


For your Volvo:

Check the charge first (1KG I think).

Next, check your compressor clutch clearance. Should be about 20 thousandths. It can be re-clearanced if needed. Excess gap causes the clutch to disconnect when the compressor gets hot, leading to poor cooling.

If that’s not it, your car has a evaporator temperature sensor that cycles the compressor on/off. Faulty reading from that sensor will cause improper cooling - either too warm or the evaporator ices up.

Sensor is easy to get to, on the driver’s side. About $38 from TASCA Auto Parts
 
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You overfilled. Not filling according to ambient temp is a common mistake. Once it got hot out, there was too much pressure and the cooling became intermittent as the compressor cycled off. A few pokes on the low pressure schrader valve (when its hot, when its acting up) should resolve it.

ACPro temp chart
 
You cant properly charge a system with only a low side gauge. You need a high side reading which you dont have. If it was low it may have only needed a couple of ounces but now you have it way overcharged. How much did you add?
 
Originally Posted By: Chris142
You cant properly charge a system with only a low side gauge. You need a high side reading which you dont have. If it was low it may have only needed a couple of ounces but now you have it way overcharged. How much did you add?


I do have legit gauges. I'm estimating I added 10 oz.

You are contradicting YouTube....
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Joking....
 
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I'll give you results after I check the pressures with my "official" CPS gauges.
 
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