Speedtoys

what does your WSM say the capacity difference is for just R12, between your car and an S4..

griffiths

Are you suggesting that a high side cut off of 464 psi is better than 350 psi? And, if so why?

What do you feel or know to be a good high side operating pressure at 100F ?

What are the differences in an S4 condenser vs. a 1981 condenser (ignoring AT and MT tranny configurations) ?

Alan

I am only suggesting that if Jake's pressure switch today is indeed cycling - then reducing the switchpoint pressure will only decrease the actual duty cycle so that even less cooling will happen - there can be no doubt about that. So we need to check the pressure or ensure better condenser cooling and see if that eliminates the issue - so we are sure this is what is happening.

As to normal design operation 464psi is very high I agree - probably too high I think. But R134a does run higher pressures at the same temperature as R12 (maybe ~20%+ higher at high temps).

I think there is a reasonable case for 400-420 psi. Practically I believe 464psi is too close to the mechanical limits of the belt drive system to be a good safety cutoff point.

I presume Porsche selected this for some reason though? (I struggle to see what). The more important changes IMO are those they made to the the fan controller. The fans run sooner and kick to high speed as the pressure goes up. This is what I think Jake's issue is rooted in. At hot idle my GTS runs the cooling fans at full speed.

Condenser styles vary over the years and depending on auto manual for size. But all were serpentine types, and all are basically undersized for the dual evaporator case IMO. All are also undersized for a Phoenix, AZ type climate IMO - but other design choices in the HVAC make this worse in practice (e.g. water valve defaulting to open with engine off).

Alan

griffiths

Alan,

Hopefully when Jake gets a set of gauges on car and notes the high side pressure when the compressor is cycling on/off "every 4 seconds" that will be a clue to his issue.

However I think you will find that a good high side operating pressure is much below the high side cut off; ie. assume at 100F, R12=240 psi and R134a 276 psi are practical operating pressures, then something at or below 350 psi are logical. If you are running R12 and see 400 psi, that would suggest an ambient near 166F which ain't gonna happen. 350 psi cut off is more practical.

"Sometimes" the oem selected a switch simply because that was what was available from their supplier or the market at the time (1981 was 34 years ago and the S4 was 29-30 years ago; R134a started with 1993 year models I recall).

Early Sharks had 'serpentine" condensers however they were discontinued; why? who knows, might have been a cost issue or a supplier issue, or Hanz in procurement got pissed off with his uncle ...the supplier.

Since you noted the cooling fan change to turn on earlier ... that tells you something. In addition to the fan lowering the pressures in the condenser, which reduces the heat, it also reduces the heat load on the radiator (since the condenser dumps heat into the radiator).

Again, after helping hundreds of Shark owners, from 1978-1992, over the past 18+ years, with R134a conversions, usually stock control devices work perfectly (whether the climate is Southern CA, AZ, NV, TX, AL, FL, Dubai, etc.) in protecting the system as well as performance wise; and my personal experiences with my past 1978, 1984S, and 1989S4 were very satisfying up to 103F humid. If all the components are working correctly, if the system is properly evacuated, purged, charged and tested... the Shark HVAC system (although more complicated than it had to be) works with R134a.

Speedtoys

...so how about a sale on an S4 auto trans parallel flow condenser?


Also..where are you located in the US? Would love to have someone that knows WTF goes on in these systems come to Sharktoberfest in Anaheim in a month..with all the parts of a system laid out (available on site) and a Tach-Talk(tm) on how it all works.

griffiths

auto trans parallel flow condenser = hen's teeth, lol.

Look, between Wally & Doc Bob notes, Nichols site, and taking your time to research and read... save your money on the Sharktoberfest, and boring Ted Talks and buy a six of Becks and and hit the links.

Speedtoys

You -pay- Internet Brands to tell us our community events are ****e?

griffiths

Omg, ruffled feathers. Shark Frenzy?
No, let me rephrase... the answers you seek are in the forums.
And, I'll assume those pieces of paper you are tossing in the video are not greenbacks, rather they are parking tickets.

FLYVMO

FWIW, the Tech Spec booklets list the capacity of the R12 system at 1050g (1200g for rear AC) for all years up to 1987. 1988 on they are reduced to 950g (1150g for rear AC).

I don't have the R134 weights handy but I bet they are about 80% of the above values.

Cheers!
Carl

Speedtoys

Not at all.

I expect a paying vendor to have a little respect for a group he wants money from.


If that's not the case, what's your reason for being here? The common good?

griffiths

Speedtoy,

If you got something to say pick up the phone , rather than puddle the thread.
You made your point.

Alan

You keep saying this, but think about it - 166F is easily possible in the heat exchanger (condenser) - and so is a lot higher - not as a true ambient, you are right about that, but that doesn't really matter. You have to stop thinking ambient means much here - it's only relevant when there is in fact quite adequate airflow, if there isn't adequate airflow then ambient temperature means little to the condenser temperature. I have said this a few times already and you don't appear to be listening, just think about it...

Remember you (and I) know nothing about the airflow Jake's (dual fan puller?) system is creating through the condenser at idle, nothing about any stock system informs us in any way about this after-market system and it's custom 1 off configuration...

Actually it increases the heat load on the radiator (by dumping more heat - that's the only way the condenser can get cooler), but it also makes the radiator function more effectively by increasing the air flow rate - so usually it is indeed a net gain. What you said here is backwards though: It is the reduction of refrigerant heat in the condenser that lowers the pressure, so if you don't cool the refrigerant enough you will have too high a pressure... In fact to reduce the pressure much you need to cool the refrigerant enough to actually be condensing it back to liquid form. If you can't cool it enough to do this your pressures will stay high and likely climb.

Alan

griffiths

Alan, you are correct on high pressures in the condenser increasing heat load on the radiator. I did not proof read my post before pressing the button.

And, I agree that maintaining the radiator at a particular temperature is best for overall power efficiency.

hmmmm....
I would guess the next question is, is Jake's condenser/fan arrangement moving air through the condenser at idle; and I assume Jake insured the arrangement is baffled so air moves through the coil rather than around it, and there is no recycling of warm air. He noted the fan should come on at 190 psi.

"If you are running R12 and see 400 psi, that would suggest an ambient near 166F which ain't gonna happen...." When I refer to a stock system working with R134a, I would use it's pressure and temperature relationship to trouble shoot Jake's system.
For example, if the 'ideal' qty of refrigerant is in the system, if there is no air in the system (a common issue), a higher than normal high side pressure would lead you to look at condenser efficiency (coil and air flow).

I guess we might know more when we have some P&T (pressures and temperatures data).

j.kenzie@sbcglobal.net

I always thought that the ambient air temp at the condenser assumes an abundance of flow of ambient air across the condenser. Otherwise it would have no real correlation to OAT. The airflow assumption may not always be valid due to fan problems, electrical problems or mechanical blockage.
Dave

griffiths

Yes and No, and the 'sort of':

When charging and testing a system you compare outside ambient air temperature to the P&T chart for the particular refrigerant.
If your high side pressure and the P&T match and vents are cold, you are done with that aspect.

Otherwise you use the anticipated P&T to troubleshoot a problem, such
as, on the high side of the system for example... condenser issues (blockage, air flow), air in the system (evacuation procedure), refrigerant charge (over charge), etc.

In this thread there is a compressor that may be cycling on and off too much.
It's been determined that compressor on/off phase is not controlled by the original drier temp switch (temperature has a correlation to pressure). A high side pressure switch is taking its place.
The question is at what actual (waiting on gauge readings) high side pressure is the PS switch turning on and off the compressor (we are assuming the evaporator freeze out switch is not doing it just yet). Possibly it is a defective switch, an improper circuit, or maybe the actual high side pressure is kicking the switch when the system hits 411psi ... which is too friggin high.
Excessive high side pressures will blow out seals, reduce the viscosity of the refrigerant oil, lower the life of the compressor (heat is not good in this scenario).

Getting back to "what is the ambient" (avg. outside temperature around the car)? That question is asked so you can look up what should the high side pressure be at that ambient.

Another reason to know ambient and the pressures is to evaluate whether their could be air in the system. IE. the system might call for 36 oz of R134a. Assuming you correctly input 36 oz of virgin R134a (you either used 3 12 oz cans or you used a 30 pounder and a weigh scale and you documented the before and after weight of the 30 lb canister). If the ambient of the day was for example 90F and the PT chart says high side should be 238psi in a perfect world and you are actually seeing 276 psi. Then either you have air in the system or you have a condenser/fan issue.

And, knowing your low side pressure is helpful as well, it can tell you if there are issues with compressor reed valves, piston/bore clearances (wear), TEV (expansion valve issues) and more. Excessive low side pressures reduce refrigerant/oil flow back to the compressor which leads to excessive compressor wear (the compressor needs a constant flow of refrigerant/oil when its pumping).