Question about AC 96' Legacy

[Bushwick]

I bought the car as a winter car last Oct. PO said the AC worked, and the AC did at least blow cold, but the car was never driven in warm temps until now.

 

Anyways, first warm up we had I noticed it felt cool, but not cold. Also noticed the compressor was constantly cycling on/off about every 5-10 seconds. Hooked up a gauge and a 134 refill can, and charged it some. It finally got COLD and will remain blowing COLD (or it's cycling on/off fast enough that I'm not noticing a temp difference), but AC clutch is still constantly cycling on/off every 5-10 seconds. It has the proper amount of refrigerant now. 

 

That's not normal on these, right? I was thinking there might be a high/low pressure switch bad. Any thoughts? 

Edited April 11, 2014 by Bushwick

[Fairtax4me]

Did you use an actual manifold guage set?

The cheapo gauges on the parts store refill kits are hardly accurate.

Proper amount is relative to outside temp. Unless you drained the system entirely and refilled with the amount specified on the AC service label, its hard to know if it really has the correct amount of refrigerant without a good manifold guage.

It could also be an issue of moisture or air in the system.

 

There is a switch. It's on top of the drier on the inner side of the passenger strut tower. They're not known for failing.

[Bushwick]

I used the gauge that's built in to the recharge hose. It was accurate when I recharged my Lincoln Mark VIII with it. The Mark was doing the same thing (on/off, cool, but not cold) and after a can that stopped the on/off cycling on that car and the gauge reflected correctly with outside temp.

 

I still had an unused can from that time, so I put that in the Legacy. It got cold from that, but still cycled. Ran up to AZ, bought another can (half size can) and put that in while watching the AC clutch to see if it'd stop cycling, but it didn't. Ended up overcharging and bled a little out.

 

Fairtax, is there a way of testing the switch? And what do you mean by manifold gauge? You mean a vacuum gauge to a vacuum port??

[Fairtax4me]

Those cheapo gauges get you ballpark at best.

 

Manifold guage set: http://www.zorotools.com/g/00091605/k-G4292136?utm_source=google_shopping&utm_medium=cpc&utm_campaign=Google_Shopping_Feed&kpid=G4292136&kw=%7Bkeyword%7D&gclid=CJmql9TQ170CFSwdOgodt0kA_w

That one is on the pricey side, but will be much more accurate than a Harbor Freight and will last longer.

 

The switch is just an On/off based on the pressure in the system. Same thing as an oil pressure switch, just set for higher pressure.

It works, since it makes the compressor switch on and off. Theoretically the pressure spring could be weak but usually the diaphragm ruptures before the spring wears out.

 

The rapid cycling generally indicates the system pressure is incorrect.

[Bushwick]

The day I tried charging the system it was only in the upper 50's. I'll check again in the next day or so (going into the upper 60's low 70's) and see where it's at, while inspecting the switch. 

 

Yeah, that's a little pricey for this car   Worse case I'll live with it. Thanks for the advice.

[Rooster2]

It has been my experience, that when the compressor cycles on and off every 5 seconds or so, that the system is low on refrigerant .At least you know your compressor is working. As others have said, the gauge on a can is a rather crude instrument, still it does give you an idea where you are at. You really need to have the outside temp in the 70's, when recharging.

 

Don't be surprised, if your refrigerant leaks out rather quickly. You may have a bad O ring seal in your system, that needs to be corrected. Use leak detector to find the problem.

[idosubaru]

the system is low or high.  too high will do the same thing - pressures aren't right somewhere in the midst of the Carnot cycle.

 

leaks are usually really simple:
Schrader valves at the high or low port

Orings on the compressor

 

replace those and the A/C is usually good for the life of the vehicle on a Subaru.  failures of other components are rare.

 

if it leaks or gets low again - replace all those parts then recharge.  they're like $5 in parts and super easy to replace.

[upnorthguy]

pressures aren't right somewhere in the midst of the Carnot cycle.

I didn't think I was ever going to hear about Carnot again after my science classes.

[Rooster2]

I didn't think I was ever going to hear about Carnot again after my science classes.

What is a Carnot cycle??

[Fairtax4me]

It's when you drive your car instead of riding the bike...

 

[idosubaru]

It's when you drive your car instead of riding the bike...

 

LOL

 

What is a Carnot cycle??

 

thermodynamic/mathematical principles that model refrigeration. google can tell all. A/C systems work by changing states (state meaning liquid, gas in this case) of fluid (air & gas are fluids). A/C systems have checks in place to make sure parts of that cycle are at the proper state to protect the system.  you don't want your compressor trying to compress liquid for an extreme example.  thus the turning on/off of the compressor if improperly charged.

Edited April 11, 2014 by grossgary

[Bushwick]

I don't think it has an extreme leak or anything. The 1st warm up we had that I tried recharging was about 4+ weeks ago, and we were followed by an onslaught of snow and cold until finally hitting the 50's-60's+ now. It's still blowing cold, but I'll wait until tomorrow (supposed to be 70; 77 Sunday) to check again as it's low 50's now. I'm not worried about the crudity of the gauge. But, it seemed before that the pressure was going too high, then it'd cut out. AZ guy thought it might be the pressure switch. I'll update after it warms up.

[idosubaru]

I don't think it has an extreme leak or anything. The 1st warm up we had that I tried recharging was about 4+ weeks ago, and we were followed by an onslaught of snow and cold until finally hitting the 50's-60's+ now. It's still blowing cold, but I'll wait until tomorrow (supposed to be 70; 77 Sunday) to check again as it's low 50's now. I'm not worried about the crudity of the gauge. But, it seemed before that the pressure was going too high, then it'd cut out. AZ guy thought it might be the pressure switch. I'll update after it warms up.

 

HA HA - yes - similar warm up - cool down/snow - warm up again we're having!  GRRRRRR!!!

 

Probably slightly over or under charged.

 

AZ guy is probably off. Some are good, but there's little Subaru experience out your way, my fathers in laws mechanic in Canton (family of 8) for 20 or 30 years said he won't work on his new Subaru. The store guys usually apply general principles to everything.  "Pressure switch".  That's fine for a Taurus or other American car, but Subaru pressure switch failure is almost unheard of.  Of course it's just a switch so anything is possible.

 

If you take the system apart for a switch though - replace the two orings at the compressor and the schrader valves.  For $5 the system will last the life of the vehicle that way once you're done.  Oring failure is most common in my experience, schrader valves (which simply have an oring at the base of them) are common too.  I think it's due to engine vibrations, heat cycles being that close to the engine.  Those orings will be brittle as plastic and all the others in the system will be fine. It's always those two.

[zombieforce]

Please dont release refrigerant into the atmosphere by blowing it out. I know most of the people here like t do their own fixes and these two mentioned are definitely the most common leaks on these cars but at least let someone with the proper equipment evacuate the system for you. Other than that go for it and measure your temp at the vent. 40 below ambient temp is another good rule of thumb but gages will tell the real tale.

[Bushwick]

Thanks for the tips everyone. Today I ran to AZ to grab a $20 tire inflater (with bonus points I had a $20 discount so it was FREE! ) for my other car coming out of winter hibernation. Anyways, pulled up in the Legacy, grabbed the AC gauge, popped the hood, hooked it up..... and the pressure range was ROCK solid I couldn't believe it! Wasn't even fluctuating the pressure. Just to make sure I wasn't hallucinating, I double checked the AC was on and then glanced at the AC clutch and it was staying 100% engaged at idle, and the needle was spot on for 70 degrees (even if not accurate, all seemed well). The 1st refill can I used had some treatment/conditioning stuff in it IIRC, and maybe I got lucky and it actually did something positive for a change? Ambient temps were warmer than the last time checked, but not blistering so dunno. Just happy it works correctly now as this will definitely get summer usage on 96 degree, 250% humidity, snow man melting days as my other car had the AC compressor yanked to clear the larger turbo compressor housing which is not fun to drive when hot out