[dmtinker]

I'm trying to sort out my A/C problems but am looking for something a bit more comprehensive that what I found on the Townsend site. Does anyone have something a bit more indepth? I tried doing a search but "A/C" is a little too vague to search on.

The thing I don't like about Townsend is that it has you check the electric at certain points but doesn't tell you what to look for if the test fails.

For example, I was to test the receiver by crossing the two wires there. The compressor should come on. Mine didn't.....so is the compressor bad, is it something else? I don't know, the article really doesn't tell you what is what....any help would be appreciated.

 

[Raub]

If you short the two wires at the receiver and your compressor does not run, then yes, your compressor is most likely bad. I'm assuming that you had the AC button pushed in when you tried it?

There really isn't much to the AC system. I just replaced all the o-rings in mine and recharged it with R134.

 

[dmtinker]

I did have the button pushed in but who knows if that's bad?.....I can tell the AC hadn't been used in a long time.

 

[ProfZ]

I tried doing a search but "A/C" is a little too vague to search on.

You couldn't have done a search using "A/C" because, with a few exceptions, you must have more than 3 characters in the search string.

Do an advanced search, with "air conditioning" as the search string (include the quotes); select the Classic 900 Workshop. You will get about 85 responses, in which most (or all) of your questions should be answered. Remember that many members of this Forum have had to diagnose and fix A/C systems, and there are only so many things that can go wrong!

If you still have questions, then post them while giving as much information as possible about the problem.

 

[djtaylor]

I did have the button pushed in but who knows if that's bad?.....I can tell the AC hadn't been used in a long time.

who knows? You do!! That's why you're testing it!

Things to test, the relay, the switch, the high/low pressure switch, the clutch and all the wiring in between.

That's pretty much it. You turn the switch on, *if* there's gas, the low pressure switch will operate (that's the one on the receiver), this will provide power to the compressor clutch via the relay.

You can either work forwards or backwards it doesn't matter but anything with electrics is just logical progression along the circuit. There's no magic at work here. Relays can get stuck, dirty contacts, corroded sockets, wires can corrode, switches can fail. You just need to check each component in turn.

It's also easy to test the compressor clutch by providing 12v to the coil wire, forget about shorting wires on the low pressure switch if you like.

David.

 

[dmtinker]

is the coil wire the one on top of th compressor?

 

[dmtinker]

who knows? You do!! That's why you're testing it!

That's pretty much it. You turn the switch on, *if* there's gas, the low pressure switch will operate (that's the one on the receiver), this will provide power to the compressor clutch via the relay.

I thought that if you jumped the wires on the receiver it would activate the clutch even if there was no gas...that was the whole point of the test...?

 

[ProfZ]

I thought that if you jumped the wires on the receiver it would activate the clutch even if there was no gas...that was the whole point of the test...?

Correct:lol:

Also, make sure you have continuity across the 2 wires connected to the temperature sensor in your top rad hose. (This sensor kills power to the AC if the engine starts to overheat.) Short these wires together while you do the above test, just in case.

You can test the clutch by pulling apart the connector on top of the compressor, and running battery voltage to it.

 

[cdaly]

I thought that if you jumped the wires on the receiver it would activate the clutch even if there was no gas...that was the whole point of the test...?

This test determines if everything else is working apart from the lack of gas. If the clutch still doesn't pull in, then there is another problem and gas (or lack thereof) may not be the issue. It may still be useful to jump those wires while troubleshooting the rest (remembering always that running the compressor with no gas will kill it).

 

[PHAT_joe]

since there are so many different threads on A/C, i just picked this one to expound on.

the past three days i have been pouring over the various posts regarding the a/c system, and i actully feel as if i know a good deal about it now as a result.

now i've narrowed my own a/c problem down to either the switch, relay, or not enough gas (or correct gas, or even a bad R134a conversion). i'm pretty sure i've put the right amount of gas in to the newly installed low pressure port, as the gauge on the R134a bottle informed me that i was "full". i've done all those relay tests like bridging #30 with #87b and so forth, all with positive results, as have i successfully clicked on my compressor via a direct wire from the battery to both the compressor wire and low pressure switch wires. i discovered that my reciever / dryer was replaced about 2 years (25k miles) before i purchased the car, as were all the hoses, including the R134a conversion. at least all the expensive components of the A/C system seem to be intact.

in addition to checking all the components for functionality, i've checked for leaks in the compressor, noting nothing unusual such as that residue that leaks out from it when it has a bad seal. now seeing that my system has never blown cold air, even after two recharges, logic would dictate that i must not have a leak, therefore the problem must be the switch.

understandably, if the switch does not work, the whole system would not work, seeing as the switch begins the cicuit. when i move to the next gate beyond the switch in the a/c circuit (the compressor i assume) and the system comes to life, it would seem as though the problem lies either in the switch or in the amount of gas.

sorry if i have been thinking out loud, but i'd like to know if i am making any sense.

finally, how accurate would anyone rate those gauges that come on the R134a cans? this is the exact kit that i used for my recharge the other day.

 

[Si]

A/c

Fair play to you guys sorting your own a/c out, i personnaly would'nt touch the a/c system with a barge pole, forget coolant/brake fluid, a/c gas is nasty sh**, if it leaks and your near by it will freeze things like your eyes on contact.

Personnaly it's the only thing on the car that i would'nt attempt myself.

 

[Raub]

Phat Joe...does your compressor come on at all?

You need to have the car running and the compressor on to get an accurate reading of the refrigerant pressure. I hook up the freon, then jump the pressure switch to get the compressor running. The compressor will then draw in the freon from the can. After 30 seconds or so, you should be able to stop jumping the switch and the compressor should stay on. You can't take a proper pressure reading unless the compressor is running.

 

[cdaly]

If your AC system has a leak, there's a good chance that air has got into the system as well as the gas leaking out. Since air doesn't liquify like R134a, pressure just builds up. So, when you attempt to charge it from a can, the pressure is already up so the can's gauge reads 'full' when little or no gas has gone in.

To properly fix an AC system with a leak, you must have it pressure leak tested {with a suitable detector} and then evacuated overnight {at least} with a vacuum pump. Only then should you charge it.

 

[Rodentmaster]

Do any of the rad. fans come on?

If LH comes on, the cabin A/C switch would appear to be O.K..
If the RH fan comes on as well but no compressor, it would then point to the overtemp switch or compressor itself being suspect.

http://www.saab-900.com/forums/showthread.php?t=47177


Good Luck
Cheers

 

[PHAT_joe]

Phat Joe...does your compressor come on at all?

Raub, the compressor only comes on when i jump it though the wire on the compressor it self, when bridging the #30 + #87b relay points and when briding the two wires by the reciever / driyer. the later two only occur when the engine is running, jumping it via the wires on the compressor will make the clutch move when the engine is off, and with the engine on the clutch will begin to spin; all sounds are normal as well. finally i think you have made sight of a big oversight i might have made: when i did my recharge and pressure test with the can, the compressor was not on, in fact i never gave this any thought! i put the engine on and cranked up the a/c controls, but the compressor was never on during the recharge process, this might be my problem. thank you in advance!

If your AC system has a leak, there's a good chance that air has got into the system as well as the gas leaking out. Since air doesn't liquify like R134a, pressure just builds up. So, when you attempt to charge it from a can, the pressure is already up so the can's gauge reads 'full' when little or no gas has gone in.

that it also a very good point and yet another one of my oversights. i don't like the sound of bringing it to someone to do this (nor does my wallet) but seeing as though i do not have any proper equipment to do and testing or a system evacuation than it might become a nessecity.

Do any of the rad. fans come on?

yes, my right hand (passenger side) fan comes on when i jump it through the a/c relay and also when the car gets hot in traffic. i'm assuming that the left hand (driver's side) fan comes on at a later time when extra cooling is required. i belive i have read somwhere that on the B2B1 engine, after 1991 and in north american trim, the second fan will activate shortly after the first one. also, form reading your previos posts, it made me wonder whether the aussie fan set up was the oppisite of the north american set up due to the fact that our driver's sides are on oppisite sides of the vehicle? finally, that link you posted was one of the most imformative ones on here, i spent two days studying it, but got a little hung up on the word "stuffed" used to describe the a/c system; i'm just assuming it means broken, right?

thank you guys, i hope i can fix this with out getting taken to the cleaners.

Joe

 

[Raub]

Joe...taking it to someone to evacuate it is not absolutely necessary. They do that to remove moisture and contaminants. If you replace the drier you should be ok. It might not function as efficiently as if you evacuated it, but it will work. My A/C is icy cold and as far as I know it had not worked in several years before I replaced all the o-rings and receiver and recharged it.

 

[Rodentmaster]

The changes between LH and RH aren't that deep or involved.
The car is primarily a LH car but the same for all major functions and setups. The changes that are made are essentially to make the car drivable in RH guise and cosmetically reversed inside. Otherwise the same.

The LH fan should come on when the A/C is selected inside the cabin, the RH fan should come on when the compressor is engaged.

Will post more later when I get home!

Good Luck
Cheers

 

[cdaly]

Joe...taking it to someone to evacuate it is not absolutely necessary. They do that to remove moisture and contaminants. If you replace the drier you should be ok. It might not function as efficiently as if you evacuated it, but it will work.

Alas, not so. An AC system works by compressing gas, cooling it while under pressure so that it liquifies and then allowing it to evaporate again which causes the cooling effect. Pour some alcohol on your skin and feel the cooling effect as it evaporates. This is what cools the air in an AC system. I can't remember the figures now (and I didn't do any car AC which might operate at different pressures) but typical high pressure would be about 100 to 150 psi and the liquid coming out of the compressor might be at 30 degrees Celsius.

Now, air will not liquify under such paltry pressures and temperatures. Instead, pressure keeps increasing in the system until the overpressure cutout triggers at about 500 psi. The pressure at the low pressure side of the compressor will never get low enough to allow the r134a in or will only allow a small amount in.

In the transport refrigeration game, whenever we opened the gas circuit (except for particular specific jobs following specific procedures), we would evacuate whe system for up to 24 hours before leak checking and charging.

When you open the system to change o-rings or receiver/dryer, you might get away without evacuating if there was just enough positive pressure in the system to prevent air getting in. OTOH, if you have a leak in the wrong bit of the system, air will have been sucked in as gas pressure drops and there's no way to get it out apart from evacuating the system.

 

[PHAT_joe]

i had an idea this morning: if there is air in the system, wouldn't it be possible to purge it by simply turning on the compressor while charging it and allowing the air to be pushed out?

i also wonder what would happen if i charge it with the air in the system? assuming the pressure in the system is already high would it be likely that i could explode the system if i add a few ounces of refridgerent?

 

[cdaly]

If you opened the high side to athmosphere while running the compressor, you'd likely push much of the air out. Then you could close the high side and connect the R134a can to the low side to charge the system. However, if there's air in the system, it got in through a leak and your R134a will just leak out again.

If there's air in the system, there'll be less R134a so less cooling. The pressures will be too high, stressing the system. If the pressure gets even higher than that, it should trigger the high pressure cutout switch (wherever that is) or, in the extreme, pop an overpressure blowoff valve (if such a thing is fitted).