dprantl

30psi/300psi @ 94 deg F ambient, that is quite good. Seems you may have some vacuum issues, your vent temps should be much lower. ~28psi low in a well charged system should translate to vent temps in the low 30F. How are you measuring the vent temps? IR gun?

Dan
'91 928GT S/C 475hp/460lb.ft

dr bob

It alsmost seems like it's undercharged. What's the sight glass look like?

jwillman

Dan,

I don't have an IR gun - next need to buy! I was using a cooking digital probe. I have not even begun to tackle the vacuum system. I have air coming from a bit of everywhere at this point!

Dr. Bob,

I did not think to look at the sight glass. it still has the plastic cover inserted. I will pull it off tomorrow and take a look. What should I be looking for? Should I see a solid flow of liquid or some bubbles? I assume 1500 rpm and fan speed 2 again?

Thanks All!

pcar928fan

Jim, GREAT WORK! Hey, didn't you break open that head controller unit and do some fixing in there? If so that will be the next EURO85 "project". It worked pretty consistently when the car arrived, but now the fan only comes on when it is in the full defrost position...that is NOT going to cut it. The compressor is working when the unit turns on (or it was a few days ago when I managed to get the thing to come on) but the last two days I couldn't get it to turn on at all... I'd like to get that working and throw a can or two of Freon in it and see what happens...maybe manually close the heater valve too. I bet the thing will work like gang busters then! Since it is a EURO car I'd like to keep the head unit of course.

WallyP

While sitting still or moving slowly (heavy traffic), the missing belly pan will increase high side pressure and decrease performance due to recirculation of hot air.

jwillman

According to Wally P's HVAC guide if the fan only runs in the defrost position it is either the blower relay or fuse. My 79 control head is considerably different than the later models - simpler. I was able to repair the trace with silver conductive paint and replace the broken compressor relay with a $2 replacment from Frys but the later ones have other failure points.

Is your car R12?

Bill Ball

The cooking probe is better than IR for vent temp. IR is not accurate against shiny black surfaces like the vents and will give ridiculously low readings (like -10F).

Tom in Austin

Jim, you da man! You have mastered at least half the 928 systems now ...

jwillman

Tom,

You are way to generous. I have touched many of the systems and not screwed them up beyond repair in most part due to the fine folks on this site who offer their time and expertice

pcar928fan

Jim,

I have a few spare relays so next time you are up my way or have a bit of time lets throw one in and see if that help the situation. I can't imagine it is just a fuse, but that is easy enough to check first and I have some of those too!

jwillman

I ran the car tonight and inspected the sight glass. It remained a snowy white. A quick goggle search seems to confirm low refridgerant.

Attached is the best picture I could get. Is this undercharged?

I guess it is time to give it a bit more. I plan to charge thru the low side with the engine running and AC on. Do I fill at idle and then confirm at 1500 RPM? I am guesiing I am not very far off so I assume a very little will go a long way.

Thanks for the help.

dr bob

Jim--

Run it at 1500 while you charge to the low side. For R-134a with no high-pressure protection switch, You'll want to stop a bit shy of the point where you have all liquid. As you get close to all liquid in the sight glass you'll 'puff' a little gas in, wait 30 seconds while watching the glass, then another little puff and watch again.

How much did you put in the first time? That should give you a little guidance on what's left.


Your early (pre-S4/GT) car depends on a mechanical fan for primary cooling air flow, and an electric fan to supplement that. At low speeds on hot days, especially with high humidity, the load on the system may exceed the capacity of the cooling air, and the high side pressure will go way up. This is the one serious downside to R-134a conversions. There are dual function pressure switches available. Good idea to do a little investigating of the later (late '93+ GTS) switches.

Hilton

He said he put in about 895g.

By my reckoning in post 27 that means its underfilled by about 55g.

jwillman

Thanks Hilton. The 895g should be close as I used 2 full cans with some lose when purging lines and then used a plastic kitchen scale to determine how much of the third can I installed (wieghed it full with fitting and hose attached and then a couple of times during the fill process. 895 came from 85% of 1050g which is the R12 fill value.

One question I have is when I filled the first time both the high and low side lines were evacuated. Do the high and low side lines seal when disconnected? I seem to remember shrader valves in them.

If not when I connect the lines to the high and low side fittings this time they will have air in them. Do I attach the fill can to the yellow line and purge up to the quick disconnect with R134 from the fill can before attaching to the lowside fitting or attach to the low side fitting and bleed out the air at the manifold using system pressure?

jwillman

okay, lots of things going on and none really good.

Hooked the car all up with a full can of R134, 1500 rpm, AC on and fan at 2. Sight glass seemed less white but I now wonder if I have a leak. I put in another full can and never got the gauge to go from white to even semi white. Pressures started out at 30ish / 175 and after adding the can were around 55ish / 300. When I disconnected the High pressure line (car off) there was a bit of foamy brownish thick fluid around the quick disconnect and in the hose.

This is my first Texas summer with the car running and coolant temp was at the upper white line. OAT is 90ish and high humidity. I also noticed I had coolant bubbling into the reservoir which was near full andI ultimately noticed I had some overflow through the tube. heater valve has been removed and replace bt petcock valave and air pump was also deleted during the process so I have a short green belt from Roger driving the engine fan. Belt seems loose but there is of course no adjustment.

I took the car for a drive and moving at 50 to 60 the temp was at 2 needle below upper white line with AC off and slightly higher with AC on.

So I dont see a sign of a leak around any fittings. Would I be able to? What about the operating temp issues? Looking forward tho thoughts on next steps.

Thanks