Randall G.

Had my '91 C2 converted to R-134a earlier today.

Ambient temperature = 74F (23.3C), center vent blowing 48F (8.89C).

Looking at the diagram below--which is for a '93 or later 964--I'm right at where a factory R-134a equipped car should operate.

As for higher operating pressures ... well, of course, I'll be monitoring for leaks/reduced cooling capacity.

The cost break-down, work performed by generic A/C repair shop:

-New receiver/dryer = $59.71 with shipping
-2 Fittings = $20.00
-AC oil = $10.00
-R-134a = $36.00
-Labor = $130.00
-tax = $5.12

Total = $264.83

I ordered the receiver/dryer from Vertex. Their website shows it as part #964-573-943-00. But, once received, I found it's some generic, aftermarket unit. Vertex scratched out the generic part number (on a sticker), and wrote in the Porsche part number. Anyway, who cares, as it fits and works. FWIW, the part # on my old receiver/dryer wasn't etched or stamped in the body--it's on a sticker. So, for all I know, Porsche uses aftermarket units, and just sticks on a Porsche part #.

Bill Wagner

Randall:

I (and I suspect others) would really appreciate it if you would keep us updated on how the system works out in hotter weather as well as the reliability of it. That price looks cheap. With the cost of the old refrigerant going up all the time, I wonder if this now wouldn't be cheaper than going with the old stuff.

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Arjan B.

All right Randall,

Now you can keep your head cool!

But there is one thing........ do you weld your targa roof for ever, or are you not going sa far??


Good luck,

Arjan
964 C2 1992 black <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Randall G.

[quote]Originally posted by Bill Wagner:
<strong>Randall:

I (and I suspect others) would really appreciate it if you would keep us updated on how the system works out in hotter weather as well as the reliability of it. That price looks cheap. With the cost of the old refrigerant going up all the time, I wonder if this now wouldn't be cheaper than going with the old stuff.

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" /> </strong><hr></blockquote>

I'll be sure to keep everyone updated, Bill. Also, feel free to drop me a line anytime, asking how it's working out.

Perhaps we can convince Drew K., recently converted to R-134a & living in hot Houston, to stick a thermometer in his center dash vent and tell us what it's reading?

Being able to charge the A/C every year (keeping the charge optimum), if necessary, convinced me to convert to R-134a. You can buy a kit for some $60 (less?) to charge R-134a yourself. And, once you have the pressure gauge, I think a can of R-134a is something like $15 (or less?). I think with the R-12 we tend to run it until it's on the "ragged edge" = barely or no longer effective, because it's so damn expensive.

On the up side, our A/C system was designed with R134a in mind (I have this on good authority = Grusse ), even if it wasn't designed specifically for R-134a (changes [minor?] in several A/C components in '93). So, the way I see it, if you spring a leak, it's not really an R-134a induced leak .... it's just a leak.

Arjan ... not quite ready to weld the top on, so suppose I'll have to live with losing minute amounts of my precious cool air. BTW, I did initially look into drop-ins before going with R-134a. Problem is, I couldn't find anyone local that worked with the stuff. And, I'm not certified to buy the stuff myself. Anyway, all things considered, I think I'm better off with the R-134a.

Kevin

Randall;

I think Adrian mentioned to use a late Honda receiver/dryer.

Randall G.

[quote]Originally posted by Kevin:
<strong>Randall;

I think Adrian mentioned to use a late Honda receiver/dryer.</strong><hr></blockquote>

Hi Kevin,

Yes, he did. But, at only $49, the Vertex unit is nearly as cheap. For all I know, it was a Honda unit. Actually, what Adrian ultimately gave us was a generic part number = ACH 33278 (this wasn't the generic number on the Vertex unit). I looked it up on carparts.com, and it's made by Four Seasons. Forgotten exactly what the price was, and can't check now, as carparts.com is down. I was slightly concerned, as the part description didn't state explicitly that it could be used for either R-12 or R-134a (unlike the one Vertex sent me, or several other receiver/dryers I looked at on carparts.com). It's probably okay for R-134a, but I would double check this before installing.

Jeff Curtis

Thanks for the receiver/dryer info. Randall! I think I'll order one today...as I'm currently in the planning stages for my 134a conversion.

DougB

I live in Florida and I have black interior so I'm very keen on properly working A/C systems. I see center vent temps in the upper 40s on the hottest/most humid days.

I converted my '90 C4 to r-134a about 3 years back. The r-12 leaked out through a pin hole in one of the engine compartment hoses. I had the hose repaired by a local A/C shop.

I flushed the condensor and all the hoses I could get access to with a product called AIR REPAIR™ A/C System Flush, replaced the drier, drained the oil from the compressor, replaced the rotted foam seals on the condensor fan assembly and put it all back together with new green o-rings from Dicount Auto Parts. I used the straight r-134 adapter fittings on the service ports--the fittings I used had built-in valves and required removal of the old valve cores.

I have a vac pump and gauges so I did the charging myself--this part you may want to leave to your mechanic or an A/C shop. It took 28 ounces of r-134a which at the time was selling for $4 for a 12 ounce can. I used ester oil (I don't recall the amount--somewhere between 5 and 8 ounces.)

I jumpered the condensor fan's low-speed resistor so that the fan runs at high speed all the time. The condensor fan usually runs at low speed and switches to high when the high side pressure exceeds 350 psi (I think it's 350 psi.) This change was needed to keep the high-side pressure from climbing when in traffic and the outside temp was in the high 90s.

I did recently have to replace the $20 mail-order drier I originally installed due to a leak. I purchased a replacement from Vertex for ~ $50 plus $15 for 3 cans of r-134a.

Some tips:

- There's no substitute for parking in the shade.
- I realize this may offend some people but expensive r-12 replacements, hot rod blends and additives are not usually worth the extra cost.
- Window tinting really works!

-doug

vilhelm

y'all are making my day...I just paid $165.00 for a receiver dryer..all in all a little over $2k in parts for my latest adventure...I'll post the parts cost breakdown tonight when I get home and pull the bill .

Randall G.

Hi Doug,

Very interesting reading--in particular, shorting of the slow-speed resistor. This trick could actually work for people that have a failed ballast resistor. On the other hand, the fast-speed fan is pretty noisy. Of course, running a noisy fan is certainly preferable to springing leaks or being uncomfortable. .

Did you short the resistor inside the relay--e.g., terminal #6 to #1, start signal for slow-speed actually starts fast-speed? More likely, I imagine you unplugged the resistor and jumped across the connector pins. Finally, it's also possible to add a switch to run the condenser fan in fast-speed at will. For example, switching terminal #1 to ground via some resistance or a diode.

I can't imagine there is one, but are you aware of any drawbacks (other than noise and some minimal increase in fan wear) to running the condenser fan in fast-speed when the load is relatively low? I doubt this would cause the (high-side) pressure to drop so low that it would trip the compressor (2.5 bar = low pressure trip = 36 psi).

BTW, the setpoint for starting the condenser fan in fast-speed is 17.5 bar (254 psi). Actually, the wiring diagram says 17.5 bar, the (shop manual) text says approximately 19 bar (270 psi). The high-pressure trip for the compressor is 27 bar (392 psi).

Bruce .... I read about your painful expense on "your" A/C thread. Sorry to hear this. An evaporator leak is pretty high up on my list of most feared failures. The guys that converted my A/C to R-134a said the system held vacuum well. So, as of now, my luck is holding out.

vilhelm

I figure I need about 2 years without a major expense and I'll be back in the black..just couldn't see not repairing the a/c.

my unit held a vacuum quite well also...but leaked gas when operating...just goes to show you a vacuum isn't the same as a pressure leak.

Randall G.

The shop manual has a detailed procedure for vacuum testing:

*****************
-Extract any pressure still present
-Align valves
-Turn on vacuum pump, run for at least 15 minutes
-Isolate system at approx. 0.1 bar (absolute).
-Turn off vacuum pump.

If the vacuum cannot be attained or can be reached only after a very long time or if the pressure increases above 0.2 bar (absolute) approx. 10 minutes after the pump is switched off, there is a leak in the circuit and this must be sealed.

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

This seems like a pretty exacting process, that should identify pretty small leaks. But, honestly, I don't consider myself on expert on the subject.

The procedure for retrofitting to R-134a specifies checking for leaks at higher pressures after fill, achieving the higher pressure by disabling the condenser fan.

When I talked to the guy at the A/C shop this morning, I asked him if he did a vacuum check for 10 minutes or so (as the shop manual specifies). He told me that 10 minutes isn't usually long enough, and--if I heard him right--he said that you need to check the system (hold vacuum) for about 45 minutes to really identify if it's leaking, and that's what they did with my car. Regardless .... I don't feel I'm that lucky, and won't be surprised if I need to fix a leak in the not-so-distant future.

Anyway, potential leaks aside--R-134a really does work (i.e., cool) well!

DougB

[quote]Originally posted by Randall G.:
Did you short the resistor inside the relay--e.g., terminal #6 to #1, start signal for slow-speed actually starts fast-speed? More likely, I imagine you unplugged the resistor and jumped across the connector pins. Finally, it's also possible to add a switch to run the condenser fan in fast-speed at will. For example, switching terminal #1 to ground via some resistance or a diode.

I can't imagine there is one, but are you aware of any drawbacks (other than noise and some minimal increase in fan wear) to running the condenser fan in fast-speed when the load is relatively low? I doubt this would cause the (high-side) pressure to drop so low that it would trip the compressor (2.5 bar = low pressure trip = 36 psi).
<hr></blockquote>

I put the jumper on the resister connector. I had a burned-out resistor that I cut the connector from.

I would expect the condensor fan may wear out a bit earlier since it's working harder. There's really no other drawback to running it at high-speed other than maybe higher than usual draw from ther alternator. As far as more airflow from the faster fan speed, you get that anyway when you drive fast.

I would think the best solution would be to connect the high-speed fan to vehicle speed and turn it on when the car has stopped or going really slow. I thing the HVAC computer actually takes vehicle speed into account when enabling the oil cooler fan.

Well anyway, sometimes the simplest solutions are the best.

-doug

Randall G.

Interestingly, the speedometer is an input to the climate control unit (CCU). But, I personally don't know what it does. It doesn't modify my interior blower fan speed, as it blows just as hard when stationary (chaps my eyeballs) as it does at speed.

There's really no easy way that I can think of to determine if the speedo input is supposed to tell the CCU to turn off the oil cooler/condenser fans at some set speed.

One way to find out would be to run the car on a rolling road, with the engine oil warm enough to run the oil cooler fan, the A/C on, and check to see if the fans quit blowing air at some set speed.

Alternatively, you could run leads from the fuse box to a DMM inside your cabin, and check to see if the 12V power supply to the fans drop off (relay repositions) at some set speed.

To be honest, I don't want to know the answer bad enough to try either one of these approaches.

Roland Kunz

Hello

There is a speed input into the Temperaturecontrol & regulation.
Its just a input to the mapfield for the regulation process for the temperature mixing flaps.

Grüsse