Rennaire upgraded a/c not running

[Dkennel]

I did a complete Rennaire a/c upgrade. Actually had RUF in Dallas install it. Great product and excellent install. ($$$) worth every $ in Texas heat.

Now less than a year though my vents blow warm.
The compressor does not kick in.
The condensor blower does not kick in.
The only thing running is the evaporator fan.
With the evaporator fan running I think my switch should be ok. Condensor blower is new. Compressor is new. Wiring and relays are old. With 911 histories I think a relay failure is likely cause:

I located the a/c relay on the fuse block and one in the smugglers box. There should be a third one for the condensor blower. Does any body know where it is?

Am I on the right track? Anything else to suspect check for? If I find the location of this third relay can I hotwire it to check?

[Tim Hancock]

While my '79 SC does not have one, I think newer cars have a pressure switch in the system that keeps the compressor from kicking on if the system pressure is to low (which would mean you have leaked out most of your refrigerant).

[Barrpete]

Here's the wiring diagram from the Bentley manual.

[Dkennel]

no pressure switch that I know of and system seems fully charged, thanks I have the bentley manual.
I am trying to locate the condenser blower relay that is indicated in the diagram... Where is it?

[rallyracer]

to rule out the obvious, the SC Bentley manual has an Electrical Component Locations sections. is it not listed in the Carrera manual?

[DonMo]

Round relay at fuse block and fused relay in smugglers box are only relays I ever found. I just had to redo the crimp connectors on the smugglers box relay cause they were causing too much resistance and tripping the relay. Once I did that and cleaned up the tarnished wire in the area around the fuse all was good. If your evaporator blower is working, your relay and fuse are fine. With the compressor not running, it almost sounds like you have a low pressure cut off that is taking the compressor out. Did you have some ac refit done with a low pressure cut off> Have you put guages on your system to see where the pressure is?

[Dkennel]

Yes the pressure in the system is fine...the wiring diagram would explain my problem with a defect in the condenser blower relay...I just don't know where the condenser relay is located

[Dkennel]

ok just answered my own question, the round relay on the fuse block is the condensor blower relay according to Bentley...
the a/c relay is in the smugglers box...I switched the round relay with the cruise control relay (identical) that did not fix it... maybe it is the relay in the smuggler's box...could it be the bi-metal switch?????
AHHHHHH anybody have a suggestion? How do I test it?

[fly944]

What is your static pressure ?

[Dkennel]

I don't have a/c equipment other than a cheapy R-134 can with gauge, that gauge showed in the red "do not charge" indicating system is full. A/c quit working from one day to the other with blowing cold one day and next day compressor and condensor fan don't run... I really doubt this is a refrigerant leak, but it may be....????

[Dkennel]

it seems ca. 70-80 psi pressure?
I don't think it is the refrigerant...

[DonMo]

Let's eliminate some stuff. Disconnect your front condensor fan unit at the connector and use a couple of pieces of wire and hook it up straight to your battery, brown is ground. If it runs, you know the fan is good, now you know you are chasing wire or relay. You can do the same with the compressor if you want but probably not needed. Then check for 12v at the temp switch green wire, if you have 12v there, you are making up through the relay, if not it is a problem between the two. You can also check the AC fan swittch for 12v on the red wire but you already said you have evaporator fan so you know that works. The other last check is to open the smugglers box and pull the relay out and look for power on the relay there. That's a $12 relay so if yours isn't a new 16A with a ATC fuse, I'd get one. Good luck. I just spent a Saturday chasing an AC problem, I know your fun.

[Dkennel]

okay that sounds like a good plan...
can I run the compressor clutch straight with 12v from the battery?
don't know what kind of relay I have in the smugglers box, what is an ATC fuse?

[Wayne 962]

A/C systems are mechanically and electrically simple. Like plumbing. With a voltmeter, check the levels at the compressor and see if the clutch is getting power...

-Wayne

[Dkennel]

digital voltmeter confirms no power on compressor, just 1 volt???
connected evaporator blower directly to 12 volt - it runs like a champ...
so no motor defect...

[Dkennel]

digital voltmeter confirms no power on compressor, just 1 volt???
connected evaporator blower directly to 12 volt - it runs like a champ...
so no motor defect...

[Dkennel]

okay I tried to be more systematic - hope you all don't mind the frequent posts-:

ran the condenser blower straight from battery - runs great

checked power on fuse #2 (13V)
checked power on green wire with engine running (1V???)
checked power on Condenser blower relay on fuse block (red round 13V!) with ignition on (no engine) AND compressor disconnected!
When I plugged the relay back in I felt and heard it click and the condenser blower kicked in...
Checked voltage on green compressor wire (13V!!!!)
Connected wire to compressor (maybe poor contact???) -NOTHING
checked voltage again down to 1V

So in conclusion: I get power to the compressor until I connect it. Is this a defect in the clutch? This is a <1year old compressor from Rennaire, do they warranty their parts? I know you can supposedly change the clutch without removing the compressor... Does my conclusion sound right. Thing that bothers me is if there is a short or something in the clutch wouldn't I blow a fuse instead of the circuit just temporarily shut down????

[Dkennel]

Oh those electrical gremlins:

just double checked everything again...
now even with compressor disconnected nothing worked...really odd to me. Reswitched ignition - nothing
then all of a sudden condenser fan kicks in as I lean on and wiggle on the oil cooler relais !!!??????!!
tried the relay over and over, switched them, no can't be the relay, no oil cooler relay does not affect it either,
back to basics...
yes 12V on fuse #2, yes 12 on relais #1, no no power on condenser, as I wiggle on cord for the connector motor kicks in, so now it seems I have a poor connection in the wiring from fuse block (relay) to condenser fan.. final check: yes, once the condenser fan runs I have 12v on the voltmeter at the compressor...ok how about I connect my little "idiot light power meter"...sure enough as soon as I connect it the condenser fan stops and no light comes on...voltmeter is of course also now showing 0V. So here is -yet another- conclusion (that I actually heard before from Jerry Woods in his 911 maintenance class), check your wiring with a light rather than a voltmeter, the light pulls some amps, a poor connection may still run current through the voltmeter but it fails as soon as you load it.

So I NOW think it is my wiring from relay 1 to condenser blower.....
the hunt goes on.....

[Tim Hancock]

Dietmar, FWIW, I had bad connections in my fuse box on my '79SC which made the AC quit working. The fuse blocks have riveted/staked attach points and mine were making poor contact. I had to clean them then restake them. They metal might look OK, but it can get a coating that will show continuity, but not flow much current. Same type of thing happened in my daughter's 924S in regards to the rear defroster. Solution was to clean up the fuse holder by scraping/filing the connections down to clean bare metal again.

I don't know 100% that this is your problem, but it sounds like it "could" be.

[Dkennel]

Okay.. back from the car.

I finally have had enought of this b.s....

I connected condenser fan directly to battery - runs great
I ran a wire outside car from fuse #2 to compressor - Compressor clutch clicks in immediately, easy to see, easy to test!!!

start up the car...within seconds I get ice cold air from vents!!!!

So my components are all working, it is not the refrigerant, it is not the switches???, well all I really know it is the wiring. I cannot get consistent power to the condenser blower, I cannot get current to the compressor that will hold a load...

Where do I continue now? remove the fuse block and check connections???
Once the connection with the condenser fan is good it runs consistenly...as soon as I put a load on the green wire it dies I can hear a relay clicking, if i just hit it briefly it kicks back in, sometimes it takes a couple of seconds and it will kick back in by itself. I cannot reproduce a short in the connection from the relay to the condenser, keep wiggling it to no avail, so not sure if that is the culprit...any ideas?????
what about a/c temperature switch??? why is it connected to the DME???