MtlSphere

The a/c was only marginally effective. I was thinking time to overhaul. So I started doing a search for a/c info on the forum. The car had already been converted when I got her so I didn't know anything about it. The compressor was cycling way too much, checked it with a gauge, it was low. Added refridgerant and the cycling became normal but the vent temps in the car were still too high. I'm thinking at least orifice tube and evaporator at this point and probably compressor and clutch to show her who's boss.

That's when I came across info about how to set up the system for the 134 retro fit. Adjustable orifice tube and low pressure switch adjustments. The orifice tube is like $2.00 for the stock and $25 for the adjustable. For giggles I decided to go ahead and try the low pressure switch adjustment...pull off the connector, there is a screw between the terminals, turn it counter clockwise 0.5 to 0.75 turns, replace the connector. I did that and ...

WOW! Instant 10-14 degree reproducable results! The vent temps were only 60 degrees prior. With this adjustment 41-45 degrees! Noticably much cooler in the car!

Thanks to the Forum and to member SunCr of San Diego specifically! :cheers:


[Modified by MtlSphere, 2:33 AM 7/25/2003]

trupp

Which switch is the low pressure switch?

MtlSphere

The low pressure switch is on the line coming from the accumulator to the evaporator on the firewall. Pull the connector off and you will see the adjustment screw between the terminals.

crheinish

I don't know where you got that information from but 1.5 turns counter clockwise is to much. The compressor will not cycle and the evaproator will freeze up. 1/4 turn counter clockwise is more like it. You can verify this by hooking up your gauges, running the vehicle at 1500 rpm, air on recirculation, fan speed low, and the compressor should cycle between 20-22 psi.

TIMSPEED

My 87 coupe has been converted to 134a..so what do I need to do to lower temps like you did? (I have a black car with a glass top!)

MtlSphere

You are right! Those figures in my first post were a typo. The correct values are 0.5 - 0.75, or one quarter to three quarters of a single turn. Thanks for bringing that to my attention...will edit shortly...

The thread that I found was thus...
http://forums.corvetteforum.com/zerothread?id=610592

The compressor cycles normally and I haven't seen any icing. I'm very pleased with my ac at this time.

crheinish

:cheers:

Stingraynut

SunCR was alos a great help to me with my blower problem – he’s the aircon Guru.

Now that I have everything working I can see that the system is not getting cold enough and the blower is not blowing enough. I think at this stage I shall take it to an aircon shop but as nobody knows C4 vettes here in Cairns, I’m trying to find out as much as I can first.

Does my 88 have this magic adjustable pressure switch ?


S’nut

SunCr

Poor cooling is allmost always a low charge. If the compressor is cycling, turning on & off more than 8 times at idle, the charge is probably low. Any a/c shop should be able to hook up a manifold gauge set and determine if there is an adequate charge. as determining the state of charge on the Vette a/c system is atypical of any GM vehicle. R12 capacity is 2.25 lbs (sorry I don't know the metric conversion). Assuming a 70 (21C) degree day with 60% humidity, the low side pressure should be about 30 psi; the high side about 180 psi, and the vent temps about 48 (9C) degrees with the engine at 2000 rpm and the radiator fan on. The mechanic can keep the main fan running by disconnecting it's switch which is on the high pressure line. If you want, find out what it's operating pressures are (note what the air temp is too) and then post them for further help.

Stingraynut

Hi SunCr,

I would say that our average day temp in Cairns is 31degrees C – 87Fahrenheit – the humidity gets very high, over 80%.

Our top temps can get to 100F with extreme humidity – you can see why I’m desperate to get the aircon working for the coming summer. (it’s winter here now and still shorts and T shirt weather)

My refridgerant is 13a, (or something like that) do those pressures still apply ?

I’ve had an aircon place recommended to me by the local car club, they have done work on Stingrays, so as I said I’m arming myself with info before going to them.

I found the pressure switch - pulled the plug off the coolant line at the heater and saw a screw head recessed between the 2 pins. Do most cars have them or is it a GM/Corvette thing ?

Thanks


Stingraynut

Slalom4me

<off topic: self-deleted>


[Modified by Slalom4me, 8:37 AM 7/28/2003]

SunCr

Don't remember it being that warm when I was there last August, but I was advised that your summers can be miserable. The pressures I gave you are for R12. If it's converted to R134, pressures will be a bit higher. They will also be higher at higher temps. For either, you can use 2.2 to 2.5 times the ambient air temp (F) as a guideline for the high side. If its 81 degrees, the high side pressure should be in the area of 180 to 200psi. If the system is HC12A, that's a hydrocarbon blend and I don't know what the pressures would be. The shop needs to know what's in it to test it and most of the facilities in the US can distinguish between R12 & R134, so hopefully they'll have that capability in Cairns too. Anyway, that screw between the terminals (common to all GM'S) adjusts the pressure at which the compressor shuts off to prevent icing. Turning it counterclockwise lowers the shutoff pressure; clockwise raises it. Really no reason to mess with it until you know what the pressures are and the type of gas that's in it, but for R12 it should be set at 25psi; R134, 22psi.

Stingraynut

MtISphere – hope you don’t mind me using your post to find some stuff out, thanks for starting it and I hope the info is helping others who are just lurking.

SunCr – I call 31C (87F) our average temp because it’s amazing how many weeks/months go by and that’s what we see on the daily weather forecast – it’s almost a joke to us.

When you were here in August, that was the last month of our WINTER ! the end of July is generally our coldest time (right now ). January is our hottest and we’ve had some stinkers.

Thanks for the pressures and info. I have a sticker on the aircon that says it was converted to 134.

Slalome4me, er….winter is shorts and T shirt, summer is…..shirts and T shirt although I skip the T shirt when possible. The council have just approved topless sunbathing on our Esplanade, it’s made ‘cruisin the ‘nard’ more interesting. They’ve ruled that girls can lie topless providing there’s no excessive movement……WTF ?

S’nut

SunCr

I thought I saw topless sunbathers all over the place? Must of been daydreaming or maybe it was in Sydney??? Anyway, now that you know it was converted, it might help to turn the adjustment screw a 1/4 to 1/2 turn counterclockwise. If it wasn't done at the time of the conversion, that can lead to subpar performance. The compressor needs to cycle off at 22 psi, so having a gauge set helps, but you can always try it and see if your vent temps drop 5 or so degrees (F). If the lines get icy or if gets cold and then goes hot at speed, you've gone too far and will need to turn it back up. No harm in trying though.

Stingraynut

Thanks SunCr , more good info. You can see I’m starting with a blank database when I called the refridgerant 13A when it’s really 134……..working on it……..

But to more important topics – Re the topless sunbathers, yes they’ve been around for years – always an enjoyable walk to see the ‘white pointers’ as we call them. I think the council decided to legalise what was already happening, but what I really like is this specification about ‘no movement’ – like, they had to think of something “OK, let’s say they mustn’t move and we’ll have no trouble” – good one – they’re SUNBATHING !!!!

S’nut

MtlSphere

My pleasure S'nut. I have found a great deal of very good information here on the forum and just wanted to pass along an "attaboy" to all concerned.

On a sad note though...I finally got the ac where it needed to be to enjoy climate controlled driving in upper 90* wheather and as a consequence I have been using it a great deal more often than ever before. Yesterday the compressor started talking to me. Yeah, she's singing pretty good. Bearings goin south...So I dropped by the Zone and ordered a compressor and clutch $99.99, new accumulator $58.99, O-ring kit $3.99, for a weekend overhaul...I'm gonna have a very busy weekend! Now here's the question...

Fixed or adjustable orifice tube? Fixed is $1.99, adjustable is $25.99. Is there really a noticable $24.00 difference there? And if so, I'll go with the adjustable but I can't find figures on what to adjust it to? SunCr...help! Also a lil help with how much oil I should add to the compressor and accumulator if they are shipped dry? Just occurs to me...will they be setup for R134a or will I have to buy the conversion fittings...OMG! What have I done?

SunCr

Could just be the clutch pulley singing and that assembly is a separate unit that can be replaced without discharging the system, so you might want to replace that first (in fact you can just replace the bearing if you want to). If the noise is gone, you'll save $'s. On the other hand, if you recently recharged or converted without finding why it leaked out or if it was leaking for some time, the compressor may be on it's last legs anyway. A good rebuild or new compressor should have oil in it - you won't know what type though - reject any that don't and aren't sealed when you buy it as some oils have a high affinity for water which will lead to early failure. Drain and refill with whatever you're going to use. Turn the shaft 10 times in one direction and 10 times in the other. Drain & repeat. Fill with 4 ozs of oil. Put 4 ozs in the new accumulator, or if everything is apart and accessible, put 4ozs in the compressor; 2 in the accumulator; 1 in the evaporator & 1 in the condensor. Some GM replacement accumulators come with 2 schraders and the bracket needs to be notched so that it fits correctly and doesn't hit the hood. GM (AC Delco) compressors & accumulators are compatible with R12 or R134 and so are the seals. The discount auto parts store brands - particularly Factory Air -have a crummy reputation and the warranty contains some fine print about proof of a system flush and a couple of other items to get them off the hook when a compressor fails and pretty much destroys everything you've replaced.

Stingraynut

More great info from the aircon guru, useful to us all, thanks SunCr.

Armed with the knowledge gained here I took my 88 to an aircon and auto electrician bloke recommended by my car club.

He seemed to know his stuff and I’m booked in for next Tuesday, but I’d like to check here to see if what he said sounds OK.

Firstly, bearing in mind my aircon/heater box is upside down, he said that the top pipe which has the electrical plug with the adjuster screw inside is the EXIT pipe. For some reason I thought it was the IN pipe.

He said I don’t have a reducer pipe but a TX

The compressor is a Nippon Denso 10 pa 20 c which is huge for the size of the cabin.

I told him that the aircon takes 20 minutes to become cold enough and that the EXIT pipe gets very cold just out of the box. From that he deduced that there is enough gas in the system and that we should check that the blower is getting 12 volts and is working well and that the evaporator is clean and doors working properly.

Seemed OK to me and something I want done anyway.

He rotated the Compressor clutch forward and back and said there was a little play there but not too bad. What should I be looking for ? How much rotationg forward/back should there be between picking up the slack ?

I’m wondering why he didn’t mention testing the pressures, as mentioned by SunCr here.

I could post this as a new thread but it seems the answers are all here.

Thanks

S’nut

NOT-MEE

Ok i just turned the little screw a little more than half and wow it chillen.My car got converted three years ago.It has never blown really coldbut thats 134 for ya .I just drove around block and it blows cold .

SunCr

For left hand drive, the evaporator outlet is on the top with the inlet at the bottom. The connection at the bottom contains the plastic orifice or restriction which is screened and meters the high pressure liquid refigerant into the evaporator. As hot air is blown across the evaporator, the refigerant boils absorbing heat. The bottom of the evaporator tube, below the orifice, should be cold and the outlet at the top should be about the same temperature or slightly cooler. Before the orifice, the high pressure line should be hot. If the orifice becomes plugged, the refigerant will boil immediately and there will be nothing left to absorb any heat. The clutch will cycle fairly rapidily under this condition and adjusting the pressure switch won't fix it. The idea is to have the refigerant metered and boil at or slightly below the freezing temp - too low of a temp, the moisture in the air will freeze and block air flow. R134 will boil at freezing at about 27 psi and 22 psi is what you want at the pressure switch, after the evaporator, for it to operate efficiently. The evaporator came from the factory with a foam filter glued to the blower or air inlet side. GM evaporators have a reputation for leaking and when they do, compressor oil destroys the foam filter and you end up with a gooey mess resulting in reduced air flow. Unfortunately, the only way to see that side of the evaporator is to remove the housing. If it is leaking though, an electronic leak detector will go off if you stick it in the vents. Hopefully, your tech has one. Jumping battery voltage to the blower is a good way to test the components that power it up. If it blows better, something in the circuitry is faulty. Check the connector first. Blowers draw a lot of amps and the wiring is marginal. If it's discolored, it's probably dropping voltage. Taking apart the connector and soldering the terminals will ensure full voltage to the blower. Factory specs on the Nippendenso compressor calls for .020 inch (.5mm) clearance (which is fairly standard for all of GM regardless of compressor) between the face plate and the pulley. It is adjusted with shims or washers behind the face plate which is held on by a 10mm bolt. The Nippendenso compressor is a stout unit with it's weak link being the shaft seal. If it's leaking, you'll see compressor oil on the hood above the compressor. In the US, the aftermarket (NAPA auto parts was where I bought the last one) supplies a seal kit which costs about 50 Bucks and if you do a Google search, you'll come up with a couple sites with DIY's showing all the steps & tools you need to replace the seal. Let us know what the tech thinks - once he hooks up some pressure gauges, he should have a pretty good idea as to what's going on (and I don't know why he didn't because most a/c diagnostics begins with that) and making sure there's decent air flow across the evaporator and that the clutch is set within specs are standard procedures.




[Modified by SunCr, 10:25 PM 7/31/2003]