ecobb993

Well, I began following the routine BS911 did a great job writing up on "Complete A/C Diagnosis" and have come to this:

No A/C - Compressor Not Running - true
Downstream
Compressor power lead - plugged in tight but no 12v at plug
Compressor fuse - good
Compressor relay - swapped a #53 (141-951-253-B) for it and the compressor started spinning nice - OK! Bought a new 964-615-215-00 compressor relay (45 bucks!) put it in - NO DICE!

So, what's the deal? Why does it work with the (wrong) relay, but not the new correct relay? I thought about making the swap permanent, but haven't been able to determine if this is a good or bad move (don't want to create more [expensive] problems).

Thoughts?

tj90

I wouldnt replace with the wrong relay. Thats asking for it. Is it possible that new compressor relay you bought is bad? Is there another 993 owner in the area that is willing to try your new relay and see if it triggers their compressor?

flankenspeil

replaced the pressure switch?

ecobb993

If the pressure switch were bad, or the refridgerant pressure too high or low, wouldn't there be no current to the relay? But when the temporary relay is in place, the compressor does get power and operates.

Sure appreciate your thoughts.

dutchcrunch

when you put the wrong relay in it worked, ok, you know that that circuit from the is good, di it run on its own without activating the a/c button in car??

take out the relay. you need the schematic and see if you are getting voltage to the relay termanals, this is powered when you activate the a/c button.

please do not do this if you are not sure what you are doing as i do not want to be resposable for any damage. all the realy does is get 12 volts from the a/c button when turneded on and the energized relay closes a swicth to let the compressor get 12 volts, so either its down stream of the relay or up stream, meanind the a/c switch on the car is bad ect. its real simple to figure out. seeing you put the wrong relay in i suspect that wires going to the compressor is good, and its up stream from the relay to the a/c switch in the car.

dutchcrunch

probably the wrong relay you put in was normally closed where the original was normally open or vice versa thats why it worked make sense.

dutchcrunch

If the pressure switch were bad, or the refridgerant pressure too high or low, wouldn't there be no current to the relay? But when the temporary relay is in place, the compressor does get power and operates.


if the a/c presuure switct is acticated i preety sure it is wired up stream of the relay and the other member that suggested it might be the problem might be right. if you are low on freon and you put that wrong relay in you are going to burn up your compressor.

the best way to tell if you pressure switch is the problem put the right relay in, find the info how to activate the low pressure switch, should be somewhere in regards to servicing the a/c, when you put the low pressure switch in by pass mode and the system works, either you really low on freon and the switch is doing its job or the low pressure switch is bad.

ecobb993

dutchcrunch,

Again, sure appreciate your ideas.

With the substitute relay in, the compressor only comes on when the a/c button is on. Turning the a/c button off stops the compressor.

I'm still confused about the pressure switch. If it's upstream of the relay and the refrigerant level is low there shouldn't be power to the relay. And if there wasn't power to the relay it wouldn't matter whether which relay was in place, the condenser wouldn't work with the a/c button pushed.

What am I missing?

dutchcrunch

you say with the wrong relay in the a/c only comes on when the switch is pushed, are you sure??? not doubting you just want to make sure? if it is only coming on when you activate the a/c button then it seems the system is ok. and maybe the new relay is bad too.


are you going to the back of the car and verifying when its on and off???

ecobb993

I'm no electrician and it's been (many) years since I studied electric circuits. So I've scanned the wiring diagram for the ac circuit. It's in 3 pieces so I could keep them large enough to upload and still make readable.

http://www.srlx.com/images/ac_p1.gif

http://www.srlx.com/images/ac_p2.gif

http://www.srlx.com/images/ac_p3.gif

Again, sure appreciate all advise.

dutchcrunch

actually, the relay has lts say 4 pins, 2 pins are the energizing relay circuit it either opens or closes a switch that is separate og the relay make sense.

now the relay switch could be configured 2 ways normally open and normally closed. thats why i asked if you went to the back and verified it was off when off was selected ond on when on was selected.

this is hard to explain. i f you put a relay that is norally closed in a circuit that only wants this comand when powered , it will be on no matter what, make sense??? actuall you off and on will be reversed.

all you have to do to see if its relay fault related is get your 12 volt meter find what pins are the energizing circut for the relay when its removed, turn switch on you should have 12 volts, turn switch off, no volts.

ecobb993

I think I've already done that:
* original factory relay - no condenser function
* substitute temporary relay - condenser function good
* new factory relay - again no condenser function

Maybe as tj90 and dutchcrunch might agree, the new factory relay is as bad as the original. I sense there's some other issue involved.

JC

dutchcrunch

you can bench check the relay, on the side or top should be a schematic of the internal relay. put 12 volts to the relay solenoid and you should hear audible click and check for open and closed circuits on the other pins accordind to the schematic. cant hurt the car as you are doing this to the relay on the bench.

before all this happened did the a/c work and blow cold air??

dutchcrunch

per my 964 companion, it states, ya i know its for 964 but should allpy to you also,

compressor clutch fuse blown
compressoe power relay failed
compressor clutch failed
wiring to copressor clutch broken or conector failed
3 level pressure switch activated due to no pressure in system
3 level pressure switch failed

ebfox

Hard to figure why one relay works and another doesn't unless you happened to buy a bad relay.

Since the compressor works with the subsitute relay in, start it up and put a set of gauges on the system. If your charge is low, charge it up and then try your other relay. If your charge isn't low, then that points back at the relay as the problem.

Good luck.