Air Conditioning Not Working

mtelliott · 07-24-2008, 06:17 AM

So, I had my A/C upgraded to R149A (or whatever it's called) over a year ago. Blew nice and cold until three days ago. Maybe I've developed a new leak however wanted to see what electrical things I should check before taking it in for expensive service.

The light comes on when I push the A/C button however the engine doesn't seem to be under any additional load after pushing the button. Maybe that's because there is a leak and I no longer have refrigerant (I'm not familiar with A/C and how it all works) and therefore nothing to really compress.

Thoughts?

Michael

gattaca · gattaca's Garage

I'm interested in this thread b/c mines been doing the same thing for many years. Would blow cold for months at a time then nothing. Had it serviced many times still acting up. Last time they put in dye. Sorry not much help...just a bump. Here's a write-up, maybe this will help: https://www.928gt.com/t-wallyhvac.aspx

rj7630 · 07-24-2008, 09:08 AM

I hope somebody weighs in here because I have justran into the same problem with my 84. I had it recharged yesterday so I know that is not the problem. I'm pretty sure the compressor isn't kicking in as I can push the AC switch and the motor never pulls down at all.

911blex · 07-24-2008, 10:09 AM

If the compressor is not kicking in, there is a good chance there is either not enough refridgerant or too much refridgerant in the a/c system as one of the functions of the high/low pressure switches is to disable the compressor so it doesn't blow a seal if if the refridgerant level gets to low or too high. It is also important to remember that with R134a it is critical to have just the right amount as your A/C won't work if you are off by more than a couple ounces (i.e. it is not as forgiving as R12).

My first-hand experience with repairing 928 a/c systems that have been converted to R134a leaves has left me with the impression that many systems end up leaking because not ALL of the a/c hoses and o-rings were changed at time of the conversion. The old-style hoses and o-rings don't do as good of a job of keeping the smaller R134a molecules from escaping.

Just my $.02.

mtelliott · 07-24-2008, 10:58 AM

I had a feeling this might be the case so thank you for confirming. And my guess is that you are correct, not all the seals were replaced.

Thank you for your input.

Michael

ROG100 · 02:45 AM

Much easier to stick with R12 as the system was designed for.
Contary to popular belief R12 is readily available.
The best write up by far is the one prepared by Walley Plumley and as per the link posted by gattaca.
As already stated the low pressure switch will stop the compressor clutch kicking in if there is low freon in the system.
Buy a set of guages and an auto HVAC manual and do it yourself - its a lot esier than you think.

Thunder · 07-24-2008, 08:38 PM

Concur with Roger.

R12 by efficiency is better than R134A by 10% +/-. The cost per pound of R12 versus changing parts, orings and such to convert the system to R134 seems the same $$. But R12 cools better than R134, and R134 does not have the same cooling capacity as R12.

911blex · 07-26-2008, 08:10 PM

Quote:

Originally Posted by Thunder

Concur with Roger.

R12 by efficiency is better than R134A by 10% +/-. The cost per pound of R12 versus changing parts, orings and such to convert the system to R134 seems the same $$. But R12 cools better than R134, and R134 does not have the same cooling capacity as R12.

Agreed. When you factor this along with the fact that real R12 can easily be bought from used parts vendors at classic car show swap meets for not much $$$, it makes little sense to do an R134a conversion.

mtelliott · 08-20-2008, 05:48 PM

Update:

So, it looks like I need a new compressor and new hose. The hose is the one that has the blue valve (behind the radiator) and runs to the compressor? I guess I'll need a new dryer since I'll have to open the system. Of course, the shop quoted me something like $1600 (200% mark up on parts).

So, the question is. Can I replace the parts myself (I've rebuilt a 911 3.0 engine from parts) given that I have to work from underneath and it's tight confines.

If I replace the parts, can I charge the system myself? After seeing what the shop does, it doesn't look terribly hard. I know you have to be competent and understand the pressures and make sure you connect properly, however it doesn't look like it would be that tough.

This would be a winter project since summer is practically over here in Denver.

Thoughts?

Michael

Danglerb · 08-20-2008, 06:41 PM

To be 100% legal you can take a simple online class for your freon license, gauges are cheap, a vacuum pump a bit more expensive for a good one, but maybe they can be rented or borrowed?

I bought my rebuilt compressor from a guy in TX that sells on ebay named John Hancock for $200 shipped without a core. Bought a set of seals (R134a conversion kit) and receiver dryer from Pelican for about $50 shipped.

If the local shop doesn't have much 928 experience, doing it yourself might be the best choice regardless.

*************

That said you should start by making a few simple electrical checks on the pressure switch etc.

911blex · 08-21-2008, 09:17 AM

Michael,

I've done this job. It's not terribly difficult, just time consuming and requires patience...definitely a great and worthwhile winter project.

In addition to buying a new a/c compressor, receiver/drier, and hoses; you are likely going to want to buy a new a/c expansion valve, a new a/c low-pressure switch (i.e so you don't ruin your new compressor due to a faulty low-pressure switch), ALL new o-rings, and a container of PAG oil to lubricate the o-rings before you put them in place. If you want to splurge, get an a/c condensor from Griffith's that is specifically designed for R134a (they also sell the correct barrier hoses for R134a).

Once you have put everything back together, I recommend having the system leak-tested. Keep in mind that you have to evacuate all of the air from your a/c system with an a/c vacuum/evacuator prior to filling it with refridgerant or your a/c won't work (i.e. freon can't compress oxygen).

Cleaning the front of your a/c evaporator is another item I recommend doing if this is going to be a winter project as you would be amazed how much gunk/grease/oil the front of it gets caked in the front the evaporator over time, blocking off air flow into it. To get good access to this, you will need to remove the hood, wiper panel, and blower motor. You can then take a toothbrush and some non-corrosive cleaner to clean the junk out of the condenser.

With the blower motor out, now is a good time to replace the vacuum actuator, the missing/dry-rotted foam in your blower box, and degrease/relubricate the blower motor (so it will spin faster).

Please feel free to PM me if any questions come up while servicing your a/c.

mtelliott · 08-21-2008, 02:28 PM

Quote:

Originally Posted by 911blex

Michael,

I've done this job. It's not terribly difficult, just time consuming and requires patience...definitely a great and worthwhile winter project.

In addition to buying a new a/c compressor, receiver/drier, and hoses; you are likely going to want to buy a new a/c expansion valve, a new a/c low-pressure switch (i.e so you don't ruin your new compressor due to a faulty low-pressure switch), ALL new o-rings, and a container of PAG oil to lubricate the o-rings before you put them in place. If you want to splurge, get an a/c condenser from Griffith's that is specifically designed for R134a (they also sell the correct barrier hoses for R134a).

Where does the a/c expansion valve and a/c low-pressure switch sit? They look like inexpensive insurance but don't know exactly where they sit. I'll pull the Porsche repair manual out to see it all however just thought I would ask before digging into.

I've heard that you can rent / borrow the equipment for evacuating the system for any major car parts house. Is this true or is it just the gages?

Thanks for everyone's advice. Guess I need to start putting together a purchase sheet. Probably not going to start the work till October so I have plenty of time to pull together parts.

Michael

Danglerb · 08-21-2008, 04:08 PM

Expansion is a deck of cards sized box between the windshield wiper motor and the firewall, can't miss it with the AC hose going in it.

Pressure switch is on the front passenger side of the condenser same as the dryer.

HF sells a set of gauges for like $30, but some have had some issues with them. Wait til fall and look on Craigslist. You may also need a decent scale to weigh the freon too.

Truth told a "good" set of gauges, vacuum pump, scale, and the class is maybe $400 and that buys you what, ONE hose from Porsche? (hint, have old hoses remade with new rubber on old metal).