I run my A/C all year long in Orlando

The first time this happened few weeks ago the air flow out of the vents almost stopped like the evaporator was iced up, classic symptom. Outside air temp was cool 55-60 (guess), I was traveling 50-60 for at least 30+ minutes which I believe contributed to the condition. I eventually switched over to just vent, the ice melted, air flow returned, back to A/C and all was normal again. Thought the cycling switch might be bad

Then 2 days ago same thing happened, same conditions except I had my Tech1 in the car. Stopped and connected it to get some readings. The clutch was not cycling off, what air was coming out was cold. But what was strange was the high side pressure was sitting at 38 psi. That is so weird, I don’t know how to interpret that as to what it really means. Went back to vent, the ice melted, air flow returned, back to A/C and all was normal again. Clutch was cycling again, high side 100+ psi looking normal.

Next day in the garage connected the gauges. Initial static pressure 75 psi, lower than summer time but ambient temp was about 65 in garage. Started it up and all looked normal cycling at about 21 - 45 on low side. High side cycling at about 75 to 110 psi. the clutch was not excessively cycling but a few times a minute. All looked OK. But when I shut down and continued to monitor the high and low side, the pressures dropped to 55psi on both sides fairly quickly. I have never seen that effect during summer time.

I'm sure the condenser was being cooled down real nicely during to the continuous driving and higher engine RPM unlike slower city street driving. Has not happened yet in street driving.

I am not rushing to adding a can of Freon yet. I would like to know more about what s going on. The low head pressure did not make sense to me unless it was excessive condenser cooling. I would have expected to see a high reading if the cycling switch did not open. I did check for leaks not too long ago, all was OK.

Comments or suggestions.

 

I had something similar going on before i let it be and stopped using it. my problem was in the wiring though. check your grounds and leads. i dont use the a/c systems in my cars vary often

 

Paul I would try sending a PM to member SunCr, he is the resident AC expert and I am sure he can provide some direction, good luck.

 

That's maybe the "best diagnostic" tip that could likely get posted today and the day is still very "young"!

 

Not a bad idea but I will give it a couple days and see if he picks up on the thread before I bug him. Just seeing what comments I get back in the mean time. I don’t have a severe problem, the A/C works and not in a big rush.

Don’t want to make any more out of it than it really is. I think it may just need some Freon but the symptoms were so strange I thought I would watch it for a while.

Had a short drive last night to, of all places, a corvette club meeting about 4 miles away. All was working OK as the head pressure never got over 125 psi. Later went to out to dinner with the club and actually used heat as it was one of our coldest nights here (5 mile drive, no A/C).

But I think the 3 day winter is over as it is warming up again.

 

I doubt it's icing and the High Side looks low, but these Systems are great at telling you when they're low on gas. Check pressures when it's at least 70 - that's where most performance charts begin. An R134 System should be pushing 170 psi to squeeze something around 30 psi through the Evaporator. Make sure you've blocked the throttle so that it's at a steady 1500 to 2000 rpms. The Main Fan on your Year should crank on at about 170 too which is important for an accurate reading and then use the Performance Chart in your Service Manual.

I'd guess there might be an intermittent at the Low Pressure Switch which is why it suddenly quit (and there's no low gas code). That's a common malady for this Year (which my '97 S10 had a penchant for doing when it was a 100 or better). If you can duplicate it in your garage, R & R the Connector at the Switch, wriggle it around; if it comes back on, a new Switch often cures it, though the Connector may be fubar too.

 

The low pressure switch is suppose to prevent you from icing at the Evaporator.. look in the FSM for low pressure switch cycling pressure's and test it with your Manifold set.

 

My thoughts also, that’s why it didn't make sense to me and thought it was a strange combination of events.
Wiring, connector and switch look basically OK.
The FSM says switch should open under 25 psi (and says 20-28) but about 21 or 22 is the norm for a R134 switch. The switch looks good at home as it is cycling the correct numbers, closes at about 45 psi (FSM: 41-51).

I was assuming the switch was closed the other day since the Tech1 said the compressor was engaged. I cannot duplicate the same conditions at home as I had while driving.

Garage got up to 60 today and about 65 or so outside. If it's a bit warmer tomorrow PM, I'll put in a can of Freon. I just think I'm on the edge of short cycling as today it cycled a bit more than yesterday.

 

22.5 is the threshold for R134; 25 psi for R12. R134 is 32 degrees at 28 psi, but superheat keeps the Evaporator from icing over. Putting a digital thermometer on the Evaporator outlet will give you the temp. A pressure temp/chart will let you calculate it. You want the superheat to keep it from flashing back into a liquid which would destroy the compressor.

Funky Low Pressure Switches look normal - at least mine did.

Get your pressures before you add any gas. An overcharge may not show up until it's really hot. At 60 and below, it should cycle. In fact, jumper the Low Pressure Switch Connector with a paperclip to keep it from cycling while your Gages are hooked up. You may get some ice, but it will give you better idea of the high because if it cycles, it'll bounce all over the place.

 

SunCr - Understand your procedure and I'll hold off adding any gas. Looks like the cool temperatures are going to stay around a bit longer than I anticipated. To cold probably to get good data and will let it warm up some. In the mean time I'll recheck the switch and just watch it all. When the time is right (a week??), I will re-post with the data and high side pressure and we will see where I am.

 

So it finally warmed up to about 70.
In the garage the static pressure was 68.
Started engine and was cycling 21 - 45, high side about 95 - 125 initially (later 140)

Jumped out cycling switch and had to rev to about 2000-2500 to get thru 200+ psi.

Drove the car the last night it was about 60-65 while watching the cycling of compressor. It was only on for less than 5 seconds. The off time was much longer. No weird things happening

I think it probably needs some gas.

In addition, my A/C system went Tango Uniform since the last post. Took me couple days to repair the programmer but all is working normal again. That slowed me down a bit from posting sooner. You can check out my repair, some interesting stuff.

http://forums.corvetteforum.com/c4-t...-repaired.html