AC Cools Fine For a While And Then It Doesn’t (1 Viewer)

[meatloaf]

2011 FJC

So while on a 200-mile trip the AC in my son’s FJC was cooling really good for about 10-20 minutes after we got on the road and then it stops cooling, we turned it off, waited about 30 minutes, pushed the AC button to turn on AC again and it cooled fine for about another 15 minutes, then hot air again. Pulled over, popped the hood to check & the compressor clutch was engaged. Sweated all the way home since south Texas temperatures have been at 100° plus these days.

Next morning, we connect the gauges on with AC cooling great, pressures at 37 psig low side & 225 psig high side, left AC running and after about 10 minutes we noticed that the low side pressure started dropping & even pulled a vacuum down to 10 in Hg while the high went down to 175 psig.

Don’t understand what’s going on here? Compressor going out even though clutch is turning? A restriction would cause the low side to go into a vacuum while the high side pressure would increase, correct? Any ideas?

 

[aztoyman]

An evaporator that is icing up will become externally restricted as far as air flow across it and have these symptoms. The more it ices up, the lower the low side will become. It may cycle off and on rapidly or stay off until it thaws enough for the pressure to rise again and cycle the clutch back on.

Make sure the condensate drain isn't plugged up. It should be dripping like crazy in high humidity. Also make sure the cab filter is clean. Sounds like your pressures are pretty normal when you first turn on the system.

 

[BMThiker]

If the condensate drain is clogged, you usually see water in the passenger floorboard. My vote is bad evap core. It's pretty tedious to replace as the whole dash assembly (from speedo cluster to glove box) needs to come out to access it.

 

[meatloaf]

An evaporator that is icing up will become externally restricted as far as air flow across it and have these symptoms. The more it ices up, the lower the low side will become. It may cycle off and on rapidly or stay off until it thaws enough for the pressure to rise again and cycle the clutch back on.

Make sure the condensate drain isn't plugged up. It should be dripping like crazy in high humidity. Also make sure the cab filter is clean. Sounds like your pressures are pretty normal when you first turn on the system.

Condensate line is dripping, my son also cleaned the evaporator by filling it with foam, etc.

 

[aztoyman]

One weird thing that happens on my wife's 08 FJ Cruiser that I have never seen on any other vehicle A/C is when it gets slightly low on charge. The passenger side vents will blow cold and the driver side is warm. Give it a booster shot of refrigerant and it will be ice cold again. Happens every two years or so.

Edit; Your pressures don't look like a low charge. Just mentioning this because it threw me the first time it happened.

 

[BMThiker]

One weird thing that happens on my wife's 08 FJ Cruiser that I have never seen on any other vehicle A/C is when it gets slightly low on charge. The passenger side vents will blow cold and the driver side is warm. Give it a booster shot of refrigerant and it will be ice cold again. Happens every two years or so.

Edit; Your pressures don't look like a low charge. Just mentioning this because it threw me the first time it happened.

I'd replace the valve cores in those fill points too. Not related to OP's problem, but slow leak on mine was the valve core.

 

[vipergrhd]

Expansion valve, back flush the evap core if you can and add oil. Disconnect line to condenser and see if metal is present (Fine) compressor might be going out too.

 

[iwashmycar]

Dumb Q, are the radiators clean? Haven been out mudding right?

 

[sogafarm]

My 80 series was doing the same thing. Took it to a shop and they replaced the expansion valve and it’s worked great ever since. It’s not cheap to replace but that was the problem. The part was less than $100 but the labor was $700.

 

[meatloaf]

thank you all for the replies…

Is there a way to get to/change out the expansion valve without having to pull the whole dash apart?

 

[vipergrhd]

thank you all for the replies…

Is there a way to get to/change out the expansion valve without having to pull the whole dash apart?

I looked this up and there is no short cuts, it's about 7-8 hours book time. If you do decide to do it replace the evaporator and the thermistor.

 

[mtnbiker4evr13]

Can confirm entire dash removal required and indeed does take 8ish hours to complete. 2 of the pedal box bolts are poorly placed(under cowl) and a real headache but surmountable. If its apart it would be good to do expansion valve and evap core together while apart to avoid a near future repeat fix.

I did evap core, expansion valve and compressor all at once 2 years ago when replacing a bad evap core for that reason at 181k miles. ~$450 in parts for Denso replacements off Rockauto. Been perfect in the 40k miles since.