Automotive A/C Question
 

The HVAC blower on my wife's Saab died on Friday. The A/C compressor had been squealing for the past few weeks, and the actual cooling capability has been weak for a while, so I took the opportunity to investigate that as well - turns out the tensioner was broken, so I fixed that too. Now the A/C blows colder - but I think it's too cold - it gets down to -3°! The secondary problem is after a few minutes, the compressor turns off, and then the system just blows warm air. I'm sure these symptoms are related, but I don't where to look for the problem. A couple months ago, I added a little bit of refrigerant hoping that would fix it, but it didn't make any difference. I suspect it may be over-charged, but I don't know if I should bleed some off or what.

http://forums.pelicanparts.com/uploa...1500174705.jpg

^^^

Usually overcharging results in warmer vent temps, not colder - super cold like than can mean very undercharged (but I have never seen temps that cold from auto a/c, regardless of charge, etc).

Do you own service set gauges, and if not, do you think you could borrow some from your local Autozone and use them (I ask because I obviously don't know what your a/c experience level is)? You really need to get suction (low side) and discharge (high side) pressure readings in order to troubleshoot this . . .

Over or under charged could be causing a high/low pressure switch in the system to trigger and cut power to the compressor clutch (if there is one present) - no way to know without checking pressures.

You need to either take it to a shop or get the manifold gauges. You probably have a temp or pressure cutoff switch on the receiver dryer.

Yep, need to get gauges on it. Pointless to try to diagnose w/o that first step. I've been going through this w my truck the last week.

Your FLAPS should have gauges as a loaner, just grab a set and see what it says.

How is the airflow?

Low air flow = low load = low refrigerant temperature = frozen evaporator coil = no a/c

What refrigerant was added?

Just had mine topped up last week. Supposed to be 1.5 lbs of coolant in the system and there was only 1/2 lbs. They evacuee the system, tested with nitrogen and refilled to 1.5 lbs. and added a dye to see if any leaks develop. Cost $190

The tec told me this is common on GM vehicles. The compressor seal will leak when the weather gets cold. I'm talking -35 ish. New rebuilt compressor is $600 and it might last a couple years or top up when it stops blowing cold every couple years.

Take it to a shop and they can figure out what is wrong.

On the surface of diagnosing this - typical condition of slight undercharge of Freon. But w/o utilizing a set of A/C
gauges - you really don't know what the system is doing. Pressure readings tell the entire story.

OR - you could take a chance, purchase a DIY Freon charge kit that's the same type as what's in your vehicle, charge roughly 4-5 oz's - see if that takes care of both of your issue's.

I took it to AutoZone and they put a gauge on it - it was overcharged. However, the compressor clutch will not kick in on it's own now. I ran a hot wire to the clutch trigger and got it to come on, so the compressor turns but it won't "compress" - it doesn't even impart any extra load on the engine when it's on.

You sure it's turning? You can hear the click of the clutch engaging and the center of the pulley starts to spin?

Pull the low pressure sensor plug off the accumulator / drier and put a paperclip in there to jump it, see if that makes it fire. You are bypassing the low pressure switch by doing this, this should make the compressor work- how to get it to suck initial charge.

Also, did you let some freon out? If it's too low it won't kick on as well.

If it still doesn't come on with paperclip, and you have power at the compressor harness likely means that compressor is gone, and you may have to flush the system out since metal is everywhere inside.

rjp

If the compressor is seized, then yes, but it sounds as if the clutch is not getting power.

Does the compressor turn by hand, if you spin the pulley center?

The compressor spins, but if I spin it by hand (without the belt) there is almost no resistance. Same with spinning the clutch by hand - it spins freely. On subsequent tests, I couldn't get the clutch to engage even if I applied voltage directly.

I installed a new compressor this afternoon. The clutch still isn't activating normally, but it will if I apply 12v to the trigger wire. With the compressor engaged, I get cold air like I should. Next up is to check the low pressure switch.

You'll likely have to charge it, paper clip time- it clutch won't activate if there isn't enough freon-secondary purpose of the switch, it also turns off the AC compressor after use since lower pressure= lower temps so it thinks everything is cold- when temps climb, pressure increases and there you go, compressor . I just hope it isn't clogged somewhere else. See how it behaves, I guess.

On a simple system I haven't ripped apart- when it's warmer out, I pop on AC on Max with recirc, put thermostat in the vent, charge it till I get between 45-50 degrees. revving engine to ensure it's pressurizing. Anything cooler than that the evaporator ices up and you're SOL for a bit.

EDIT: charge with paperclip jumper over low pressure switch, that's how you get it to start accepting freon....

Crude, but effective.

rjp

I got it to charge by jumpering the clutch. It has pressure now, and gets cold, but won't do it by itself - the only way the clutch will engage is if I hot wire it. I tried the wire-in-the-switch trick but it didn't work.

check fuses? You don't have power at the clutch.... Anything else electrical in the car that is dead?

rjp

There are likely some other 'conditions' that need to be met before the compressor will start, the cooling fan(s) are likely first on the list, and your interior blower fan will also have to be on.

If either of those signals is lost the clutch won't pull in. There is likely a troubleshooting guide on a Saab forum somewhere.

off course it blows -3 F, it's a scandinavian car.
They think -10 C is a nice spring weather and they break out short's and t shirts.

All the fuses are intact, interior blower is on, etc. I am going to call some shops this morning.

Does the ambient temperature display the proper temp or close to it? If it is out of whack, the compressor will not come on. Typically, when they fail they will give a -40F or so reading.

Head may be blown up as well. Won't turn on compressor. Junkyard time...