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AC repair

2K views 17 replies 3 participants last post by  sp53 
#1 ·


Hi all I am trying to fix the electrical aspects of my AC and was wondering if a relay goes bad can it cause a direct short or odes it open the circuit, perhaps it depends. When I test at the fuse (by removing the fuse) for a ground (short) on the right side of the contacts by putting an ohm meter there and ground the meter tests positive for continuity. If I unplug the single wire at the AC I still get the same problem. This tells me the probably is between the two, the right side of the fuse and the AC and perhaps the relay. I am just kinda playing around trying to fix this AC, so if anyone has any suggestions I would appreciate it.

Thanks in advance Steve

 
#2 · (Edited)
sp53 said:


Hi all I am trying to fix the electrical aspects of my AC


That's kind of a tall order. You'll need to start with an accurate and complete wiring diagram for your year and model.

As a general rule, you can't use an ohmeter to test a circuit until you're sure you've isolated the circuit.
A voltmeter will allow you to watch the voltage drop all through the circuit to make sure it reaches from the + battery post to the - post, dropping voltage where it should.
 
#3 ·
Can we start at the beginning?

In order for the relay to operate, there first has to be refrigerant in the system in order to close the low pressure switch. Once that's closed, then there may be power to the relay circuit if the AC system is turned on.

So the very first question is, "Does the AC system have refrigerant in it?" followed rapidly by "how do you know it has enough to operate the LPS?"

You can manually jump the switch in order to see if the compressor clutch engages. If it does then that suggests that there's no refrigerant (or lubrication) so don't run it like this.

In answer to your first question, the relay circuit could fail either open or short circuit since all the relay is, is a coil of wire. Should the wire fail short circuit, typically by melting the copper enamel then either the fuse should blow or a wire somewhere else will melt. Open circuit is a typically more common mode of failure due to either a bad connection or a momentary short followed by a burning through of the coil.

Does the clutch on the compressor engage when you provide 12V to it? If not it could be the air gap that is too large but then that's usually a summer problem.

Is it manual AC or ACC?

David.
 
#4 ·
Hi Dave, right on, you gave me a place to start. I will try jumping the compressor; I assume that I do that right at the compressor by putting power to the blue wire. When I bought the vehicle, the fuse in the box was toasted to the point that the plastic around it melted. I figured that someone tried either eliminating the fuse or was working on the unit and wired it direct to trace problems. Anyways the dirve belt was also missing. I pulled the glove box and looked for a toasted wire behind the fuse and could not find one. I do have a complete wiring diagram from Saab and yes the vehicle does have the ACC. I am assuming the unit does have refrigerant in it just because the vehicle was one owner and has low miles. I am not familiar with your terminology of what a LPS is perhaps you could explain.

Thanks in advance Steve
 
#5 · (Edited)
sp53 said:
I am assuming the unit does have refrigerant in it just because the vehicle was one owner and has low miles. I am not familiar with your terminology of what a LPS is perhaps you could explain.

Thanks in advance Steve
Don't start with the assumption that there's refrigerant in the system! That really is the very first place to start. LPS is Low Pressure Switch.

Some blurb on ACC http://www.thesaabsite.com/9000/9000ACC1.htm but I really feel that step one is check the system for refrigerant because if that's not sufficient or has totally leaked out say through a hole in the condenser then the low pressure switch won't be closed and therefore nothing will happen.

However, there's something pretty significant in what you've said.

Evidence #1 burnt fuse
Evidence #2 belt missing

Sounds to me like the clutch burnt out on the compressor causing the bearing to seize which blew the fuse and threw the belt. Or the belt has been removed because the compressor is seized. Or the compressor could have seized through a lack of oil due to a lack of sufficient refrigerant.

I'd try testing the resistance of the clutch, then energising the coil using a seperate lead from the battery to see what happens, you might want to add a fuse in there too so that you don't burn this bit of wire!

Could be up for a new compressor.

David.
 
#6 ·
Hi Dave and thanks again. I can turn the compressor over by hand. Does that mean anything? Perhaps what you are saying is when the clutch does engage the unit locks up. In addition, I was looking through the pervious owners papers and noticed she had a new idler pull put on for the AC? I will look at the web you suggested and get back to you later; I have to get ready for work.

Thanks Steve
 
#7 ·
sp53 said:
Hi Dave and thanks again. I can turn the compressor over by hand. Does that mean anything? Perhaps what you are saying is when the clutch does engage the unit locks up.
Quite, if the clutch isn't engaged then the pulley should just freewheel but you won't be turning the compressor by hand, it's when it engages that the compressor is engaged.

David.
 
#8 ·
Hi Dave and thanks for helping. I ran the check at the ACC ( how cool) and it displayed a single 1 and that was all, no letter with it. In addition, when you say engage the coil do you mean run a hotwire to the fuse box and by pass the ACC. In addition, how much resistance should I feel at the clutch? Do I need to put a belt on the pulley or perhaps grab it with a well protected hand and do a feel test? I put a fuse in and was thing about buying a belt and perhaps just trying to run it, and see what happens. However, I am learning as I go and appreciate the input greatly.

Thanks in advance Steve

 
#9 ·
sp53 said:
Hi Dave and thanks for helping. I ran the check at the ACC ( how cool) and it displayed a single 1 and that was all, no letter with it. In addition, when you say engage the coil do you mean run a hotwire to the fuse box and by pass the ACC. In addition, how much resistance should I feel at the clutch? Do I need to put a belt on the pulley or perhaps grab it with a well protected hand and do a feel test? I put a fuse in and was thing about buying a belt and perhaps just trying to run it, and see what happens. However, I am learning as I go and appreciate the input greatly.

Thanks in advance Steve

To engage the clutch, run a wire from the battery (via a fuse) to the terminal on the AC compressor. In terms of resistance, if you can turn the pulley by hand, I can guarantee you that the clutch is not engaged and all you're doing is turning a pulley on it's bearings. You'll see the clutch gap close and it will give a pretty loud "clack" when it engages and you will not be able to turn the compressor if it has engaged. No need to have the engine running at this point just to see if the clutch engages, it's just an electromagnet.

If you do put a belt on it, be prepared to stop it pretty quick as I do suspect that the compressor has seized which was the beginning of all of this and the reason why there's no belt on there now.

David.
 
#11 ·
Hi Dave and thanks for your help. I hooked up a wire from the power to the compressor and the clutch engaged with a mild metallic clunk. I did that a few times and each time the engagement sounded proper. Next, I engaged the clutch and then turned the pulley by hand to feel what holding power it delivered. The grab was not very strong; however, I did not leave it engaged too long. Moreover, I briefly engaged the clutch and also spun the pulley and the pulley spun free with the clutch engaged. I am not sure where to go from here. Do you have any suggestions? I would like to mention that the ACC does offer the ability to go from 82 back 62 degrees F if that makes any difference.

Thanks in advance Steve

 
#12 ·
Stick a belt on then and do the same, see if the compressor turns under load. I'd be inclined to check that the system has refrigerant before fiddling about with electrical stuff.

As i've said, if there's no refrigerant, the low pressure switch won't close and nothing will ever work. Even if you jump the switch to check that the clutch engages, all you've confirmed is that the electrics work, it still won't do anything unless there's refrigerant in the system.

David.
 
#13 ·


Thanks again Dave I will give it a try. I probably should mention that I jumped the compressor directly form the Battery and not at the fuse box. Should I try jumping from the fuse box or did I pretty much do that the way I jumped it. I guess my concern is the condition of the wire as it leaves the box and goes to the compressor.

Steve
 
#14 ·
You've proved that the clutch works, if you start the engine with the clutch engaged, you'll see if the compressor runs and you can continue to check the electrical circuit back but none of it will be much point if there's no refrigerant so hence my feelings that you might as well get that checked as the first step because that could be all that's stopping it working in the first place!

David.
 
#15 ·


Hi Dave and thanks again you have been a great help. I guess what you are suggesting is that I take the vehicle to a shop and have the refrigerant check. I have no experience with an AC system, so I am not sure how to check it. Out West here evidently one needs special permission to install refrigerant. Anyways, I will do some research and find a shop. In your view, how much would one spend to revitalize the AC refrigerant? I realize we are on the other side of the pond, but I am curious.

Thanks in advance Steve
 
#16 ·
I get mine done by a chap that comes to the house, charges me 45 quid which is about $90.

Any AC shop will have guages that they can put on the system to get an idea of refrigerant fill, they'll soon tell you if it needs anything adding. (In my case, my 9000 needed a load removing as it was over charged).

Honestly, one of two things will happen, it will either start working because the pressure switch that is a safety cut out in case of no refrigerant will be activated and the whole system will work, or you'll have a system with refrigerant and can then start to debug the electrics with a known starting point.

David.
 
#18 ·
Hi Dave well I placed the belt on the AC and put a fuse in the box then turned the ACC to 62 and nothing happened. You mentioned that this would probably be the case. I am curious would the vehicle sense if the outside temperature was say 35 F and not allow the AC to come on or is it that LPS switch you mentioned. I did note that the AC clutch did move either. I think I will leave the vehicle as is for now and wait for summer/spring before I do any more with AC. No sense fixing that aspect until the weather is a little warmer besides the tranny might need to be replaced. I am just going to drive it until I am sure the tranny is gone.

Thanks Steve
 
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