griffiths

Alan. Sorry. I'm discussing in the context of conversions to R134a.
That means any Shark prior to 1993. Jake has an R12 car converted.

Oh, I agree that if you lose a cooling fan things are going heat up pretty quickly, especially if you are sitting in 100F ambient. But, in the context of the thread,
'normal' means everything works, and most operations happen under 100F for the majority of owners and rides. I've driven my Sharks in 100F+, stock pressure switches, R134a, things never heated up and the cockpit and vent temps were very comfortable.

I guess will have to agree to disagree, if you wish, on what is normal high side at a given ambient.

"R134a conversion was a mandated requirement ". No. It was never mandatory as a "conversion". R134a became mandatory in new production cars late 1992 and starting 1993. The EPA did not say you have to convert to R134a. You can still buy, charge and run R12. R134a is simply an optional SNAP approved alternative to R12 that is easier to find and less expensive than R12.

I'd be interest in hearing what Jake has to say with regard to changing the stock PS and his charge condition and pressures of cycling.

Alan

I think you are completely (deliberately?) missing my points which are all perfectly relevant. If your definition of normal operation falls apart somewhere above 100F you are excluding huge swaths of the country that routinely see way above this every summer. I want a car that works perfectly everywhere the factory original does... I think that is a quite reasonable expectation (actually the factory original is even a bit marginal to be honest )

R134a was not mandatory - you are quite correct, but a change from R12 was mandatory for '1994 - so Porsche was facing a change mandate away from R12. R134a happened to be the easiest conversion for them to make (so really the distinction is a bit pedantic in this case).

I never suggested conversion of existing R12 systems was mandatory. However it is very relevant in looking at an R12 -> R134a conversion to consider what Porsche themselves did for this conversion. They actually did quite a bit to manage the system pressure better.

Since Jake has a non-stock cooling fan controller - "normal" w.r.t. fan operation is in fact a quite meaningless concept. You seem to be obstinately ignoring this. If you have insufficient airflow through the condenser your 'effective ambient temperature' will be much higher than actual ambient because you are achieving insufficient heat transfers. This point is quite fundamental.

I know how high the system pressure can be in a R134a car - I have one - and have experienced it. If I were converting an R12 car I would simply adopt the Porsche configuration - It is not so hard to do. The switch/sensor components are available, the same fan controller is used just slightly differently configured. In a separate thread it seems Jake is adapting the dryer connections to use the stock GTS R134a pressure switch - I think this is actually a very good idea.

Lets see what happens when the condenser is better cooled at idle. Then we may know the cause of the compressor cycling.

Alan

griffiths

Alan,

I read your points.
I'm not being stubborn (obstinately).
I respect your thoughts.
But, we have helped convert over 400 clients 928's to R134a (and my 3 sharks I had over the years) and never changed a pressure switch or modified the circuit, and they are all doing quite well.

Mute point in Jake's issue however Porsche, and every other car mfg'r, selected R134a because that was the "primary" alternative the refrigerant market offered (pushed) at the time and SNAP approved.
I believe the shop manual notes R134a in 1993, non rear air would be 860 grams and cars with rear air 1050 grams. And, I guess Jakes 81 would be about 860 grams of R134a as well (can't find my other section of the shop manual); TSB 9501 is kinda helpful on suggested initial charges of R134a.

Maybe its important to a reader, maybe not, but I believe Jakes initial post is quoting the on-off pressures of the switch and the trinary function for the fan he connected to, rather than what his actual gauge pressures are.

If you can advise us, with regard to a stock 1981 model, what cycles the compressor on and off (if that happens)?
And, what situations or circuits turn on the front blower fan; I'll assume the aux blower fan comes on when either the radiator's temp sensor or the original temp switch on the drier make contact.

Alan

I did already cover that. On most years - including '81 - only the low pressure refrigerant switch and the freeze switch control the clutch when AC is activated. There is no modulation on any year related to cabin temperature control. Stock R134a cars add the high pressure cutoff too.

For the cooling fan control - it's really not so relevant to this case because Jake does not use the stock system.

The stock system is a viscous clutch radiator puller fan and a single electric pusher mounted on the AC condenser. The fan is controlled on/off only via a relay controlled by either the coolant temp switch OR the refrigerant temp switch either one can turn it on.

That you have converted 100's without major issues means it works adequately well most of the time. I don't (and didn't) dispute that. However I don't think that is at all incompatible with what I said - which was essentially that it is not the ideal way to do it, and it likely won't work well for all conditions. Try bringing your car to Phoenix in the summer time - you may well find out exactly what I mean. Also if a cooling fan fails you may overpressure enough to blow out an AC line - nothing limits the pressure.

Late '93 models are the first with R134a - early ones don't have it. There are separate wiring diagrams for each version. I assume they implemented in mid '93 model year as they would likely be selling these well into the '94 model year. GTS Cars were actually selling quite slowly at this time - my car has an in service date well over a year after its build date.

I agree that actual gauge pressures as it cycles would be good to know, and would likely be conclusive about the cause also.

Alan

griffiths

Allan,

Sorry again, I need more coffee, or maybe its time for a Becks.

If I had the time I'd drive out to AZ, some nice golf courses out there. But, it would not be fair because I sold the last shark years ago and I'd be arriving in a modified air cooled, but the AC would work just fine for 100F+.

Getting back to Jake's issue, 'at idle compressor is cycling on and off every 4 seconds'. I would imagine with a stock temp switch on the drier, that was originally considered for R12, if one was using R134a and system pressures were a bit higher, the switch would still make contact and turn on the aux fan when its specified temperature was reached. But then again you noted Jake is using the low side feature to replace that function? or maybe Jake is substituting something for that feature. Or, maybe on the opposite side, if the evaporator core temp is getting too cold, the freeze out sensor could turn on and off the compressor as well. I guess we'll have to know what the low and high side pressures are when that happens. And, if we hear how much refrigerant was put in, and what the ambient temps are when the pressures are noted, I would imagine someone could figure out what the issue is (too much refrigerant, excessive air, circuit, etc.).

So, can you advise if it is normal, on a stock system (no modifications to circuits) for the aux fan to come on when the system or engine is already warm and the ignition switched is turned on?

Ducman82

I plan to ride the motorcycle to robs tomorrow to pick up the pressure gauges. Greg and I filled the system per the workshop manual levels for a 134 car. (I'll have to check that for how much. I want to say 32oz....)

The fan was coming on when power was applied via the ignition switch. I took off the pressure sensor connector, fan died. Tried the coolant sensor, fan stayed on. So that tells me after shut off and sitting for awhile (I'll have times on that soon) the system still had 150-190 psi in it... Till later on when the system cooled off.

I never did replace the freeze switch in the evaporator.

Alan

I don't know exactly what controls the fan on the new controller. In the stock '81 case it was just a refrigerant temp (on/off switch). On later S4 R12 dual puller fan systems models it was refrigerant pressure sensor for the variable speed fans (+ the coolant side as well of course). Since Jake has updated to a new pressure switch (even before the GTS switch I believe) I'm not certain there is now a pressure item in the fan control (mid range pressure point for higher fan speed). Only Jake can answer exactly how it is supposed to work, but from his comment in the last reply it would seem there is a pressure component now, perhaps only a pressure component for the AC trigger?

Alan

Speedtoys

You dont have...a 134 size system however. It has a different volume...right?

Ducman82

dont see how its different.

griffiths

If you have the trinary switch inserted in the high side of the system, and wired to turn on the aux fan when pressures reach xxx psi (after compressor outlet), then yes, you will have residual high side pressure in the system when you turn off the system (engine off)..... until the system equalizes (sooner or later the high side will bleed through the TEV into the low side).

When you get a set of gauges, let us know what the high and low side pressures are at idle and the ambient temperature when you notice the compressor cycling quickly as you did.

On a side note, why did you change the stock ac controls (pressure switches)?

Ducman82

i swapped my early condenser to the later S4 style, so the drier is different and has no previsions from the thermal fan switch from the old system. so i needed a pressure switch that could control the fan as well. the stock late model switch was way to expensive. so i went aftermarket.

should have gauges today.

griffiths

Okay Jake.
You are suggesting your PS does the following:
Won't allow compressor clutch to engage when pressure is below 29 psi or above 411 psi.
On that feature if you can find a switch that kills the compressor near 350 it would be better.
With regard to the fan on at 190 psi, lets see how the pressures look overall when you get your gauges connected.

Again, it would be nice see the data, after the compressor has been running for about 10 mins or so at an outside air temp above 80F:

At idle, windows up, AC max cold setting:
Outside air temp =
Low side psi =
High side psi =

Speedtoys

A 134 car is years newer than your car...different hardware.

Alan

The stock GTS R134a 3 way switch is:

Low Pressure Cutoff: off@ 22psi on@ 29psi
High Pressure Cutoff: off@ 464psi on@ 377psi

Fan Switch (to high) on@ 261psi off@ 203psi

For this case reducing the high pressure cutoff point is likely to induce lots more compressor cycling, not less.

Like I said Porsche's R134a configuration is a lot different than R12.

Alan

Ducman82

well marginally. diff oil, drier and condenser is upgraded etc.. but the lines, evap, compressor (just diff seals) are the same. from what i can tell. but what do i know.. :-P


i failed to make it south this weekend to snag the gauges. family time and all that... :-)