help interpreting pressure readings

[msrichmond]

I decided to go back and check my Fiat home-brew system after a week - I think I might have a leak.

I got another 12 oz of R134a in the system - it took a while but I was patient and it went in.

Even though the humidity is only 30%, with the front windows down (in the garage) I got a lot of condensate on the floor.

My first reading with the engine running at 1500 RPM was 30 PSI low side, 200 high side.

I got another 12 oz of R134a in, and it changed to 32 PSI low, 275 high. By this time, the engine and the area around it was really hot. I did have a window fan in front of the radiator, but my own fans behind the radiator were doing a pretty good job of moving air as far as I can tell.

Ambient temp was 92 degrees. Vent temperature was 48. It's a little tricky to measure because the evaporator coils are right behind the vents, and I assume you want to measure the air, not the fins of the evaporator.

I think it's too bad I can't measure these pressures on the highway, because I think I would get a lot more airflow at speed.

I want to test that theory by hooking up an indicator that comes on when the fans do, and when the compressor does.

The fans do cycle with the trinary switch, kicking in at 250 and then stopping when the pressure drops below that. But once everything got really hot, the fans just kept running.

Do the pressures off mean anything? They read 45 low, 160 high before I took off the gauges.

[tbirdtbird]

275 hi at 92F is overcharged.
Your vent temp is not where you want because of too small a condenser, as we have mentioned.
Not sure why you think you have a leak.
I have stated many times, bite the bullet and get a sniffer, they are so quick and easy to detect leaks, and I think more accurate. Forget the dye, the goggles, the special UV lite, and the cracker jacks. It is just cumbersome and very old school.
Off and idle pressures have no meaning at all.
You did not mention vent with first set of readings.
If you can get your hand on the pipe into evap and pipe out, they should feel equally cold.
With all that condensate, then your unit IS getting cold
Forget the indicator, you are making this into too much of a science project from 11th grade

[msrichmond]

275 hi at 92F is overcharged.
Your vent temp is not where you want because of too small a condenser, as we have mentioned.
Not sure why you think you have a leak.
I have stated many times, bite the bullet and get a sniffer, they are so quick and easy to detect leaks, and I think more accurate. Forget the dye, the goggles, the special UV lite, and the cracker jacks. It is just cumbersome and very old school.
Off and idle pressures have no meaning at all.
You did not mention vent with first set of readings.
If you can get your hand on the pipe into evap and pipe out, they should feel equally cold.
With all that condensate, then your unit IS getting cold
Forget the indicator, you are making this into too much of a science project from 11th grade

OK, that's funny, and more than a little true. I am going to throw out the AC parts of the dye kit (I bought it years ago because I wanted to find oil leaks).

In my first go-round, a week ago, with a garage temp of 95, I had 35 PSI on the low side and 285 on the high side.

When I went for a drive, with an outside temperature of 99 and with the fresh air vent closed, I got the inside of the car down to about 78 which felt pretty good. The vent temperature at 40 degrees.

The reason I did the recharge was because I thought the system was losing effectiveness.

Today's projects: clean up the dye mess I made and order a sniffer. And clean the BBQ.

Thanks for your patience and your explanations.

[Cusser]

When I went for a drive, with an outside temperature of 99 and with the fresh air vent closed, I got the inside of the car down to about 78 which felt pretty good. The vent temperature at 40 degrees.

Vent temperature is 40F ???? I think that it's time to stop messing with the system if it doesn't leak, that's pretty decent.

[msrichmond]

When I went for a drive, with an outside temperature of 99 and with the fresh air vent closed, I got the inside of the car down to about 78 which felt pretty good. The vent temperature at 40 degrees.

Vent temperature is 40F ???? I think that it's time to stop messing with the system if it doesn't leak, that's pretty decent.

I agree, but those were my first measurements last week. After a few days of driving around, it didn't seem to be cooling as well.

[tbirdtbird]

Agree with Cusser.
You were trying to find oil leaks? Please know that the dye for oil leaks is NOT the same as dye for Freon leaks, just for the record.
We had a poster here 2 yrs ago who used the oil type for his AC and basically ruined his entire system

[msrichmond]

Agree with Cusser.
You were trying to find oil leaks? Please know that the dye for oil leaks is NOT the same as dye for Freon leaks, just for the record.
We had a poster here 2 yrs ago who used the oil type for his AC and basically ruined his entire system

When I bought the kit 20 years ago, it included separate dyes for oil, coolant and AC. Over the years, I used the oil and coolant dyes. This is the first (and last) time I tried using the special hose, AC dye and syringe for the AC dye. I even went and found the now-out-of-production plastic syringe to purge the air out of the special yellow hose supplied in the kit when the original syringe didn't seal.

I could not get the yellow hose to work on the fitting... it clipped down fine, but pressure on the syringe while the compressor was running (per the instructions) did nothing.

So then I tried pouring a little dye into the charge hose. That's how I ended up with dye everywhere; the yellow hose was not tight enough on the gauge set and refrigerant-launched dye went flying. But it is the right kind of dye.

Into the trash it goes.

[msrichmond]

275 hi at 92F is overcharged.
Your vent temp is not where you want because of too small a condenser, as we have mentioned.
Not sure why you think you have a leak.
I have stated many times, bite the bullet and get a sniffer, they are so quick and easy to detect leaks, and I think more accurate. Forget the dye, the goggles, the special UV lite, and the cracker jacks. It is just cumbersome and very old school.
Off and idle pressures have no meaning at all.
You did not mention vent with first set of readings.
If you can get your hand on the pipe into evap and pipe out, they should feel equally cold.
With all that condensate, then your unit IS getting cold
Forget the indicator, you are making this into too much of a science project from 11th grade

Could having the fittings so close to the 600 degree exhaust manifold cause higher high-side pressure?

[tbirdtbird]

Ya know, for some reason, I am just now seeing this question and pic.
Of course, an AC line being close to exhaust equipment will most assuredly increase the hi side pressure. Or low side pressure.
INSULATE now. We would usually use fiberglass based exhaust wrap, it comes in rolls….have at it!!

We had a guy last summer that had his accumulator and piping right on top of his exhaust who was obviously having trouble with performance. We finally figured it out from pics what was going on. He was mysteriously reluctant to step up to the plate and do the required insulation.
You can have the best engineered system, and if you surround it with exhaust piping and such, it just won’t work. Seems like common sense but he didn’t want to believe us.

[JohnHere]

My first reading with the engine running at 1500 RPM was 30 PSI low side, 200 high side.
I got another 12 oz of R134a in, and it changed to 32 PSI low, 275 high.

The first set of readings is ideal. The second set suggests a serious overcharge, as already mentioned--probably ~12 ounces (!!) too much.