73 Trans Am r134 retrofit cooling question now that summer's here

[jlutz455]

Hi,

Converted my car from r12 to r134 using classic auto air upgrade sanden compressor, parallel flow condensor back in sept 2016, I set POA valve to 26 psi., car has original clutch fan with new fan clutch. System is charged with 134 to 80% of r12 charge.

It's been working great in FL while the humidity and temps were low, but now that its in the 90's, doesn't cool as well especially in traffic, but is better on the highway. In cooler FL months, got 44 deg from center vents on 80 deg days, 50% humidity with fan on low speed. Inside temps higher with fan on high speed.

Put gauges on yesterday with 95 deg ambient and 65% humidity and got:
Low side was 30
High side 175
Clutch fan wasn't engaged. Once clutch fan engages, pressures drop.
fan speed in car was on high. If I set fan speed to low, low pressures drop to 26 psi which I think is correct because it matches my POA valve setting.

Looking to see if these pressures make sense and if this is the best the system is going to get, or there's room for improvement.

Thanks!

Jeff

[Cusser]

now that its in the 90's, doesn't cool as well especially in traffic, but is better on the highway.

Clutch fan wasn't engaged.

This would help explain why performance is decreased when in traffic - that's when you need the fan clutch to spin and the fan to be spinning to help cool that condenser. At highway speeds, ram effect cools that condenser.

Put gauges on yesterday with 95 deg ambient and 65% humidity and got:
Low side was 30
High side 175
Clutch fan wasn't engaged. Once clutch fan engages, pressures drop.

Your high side pressure is pretty low, especially if the clutch fan was not engaged; were those readings taken at about 1500 - 2000 rpm ???? So to me sounds like you have a leak somewhere. Find leak, have system charged by weight. So maybe time for a real AC shop which has the right equipment to do that.

[bohica2xo]

What do the pressures look like under full load?

Doors open, cabin fan on highest speed. Raise engine rpm to 2000. Hold for 90 seconds or more & record pressures at 2000 rpm

.

[jlutz455]

oops forgot that part!

At 2000 rpm's the low was 35 psi and the high was 200 psi, before the fan clutch started working then the pressures dropped. I had the doors closed and ac on recirculate. I'll have to do again with doors open and fan on high.

When I first charged it last september, i pulled a vacuum to 29" and it held for 30 min and closed to valves to see if vacuum held. It did, so then I pulled a vacuum for another 1 hour. I charged the system with 80% of r12 charge using the large r 134 container and a scale to get before and after weights of the container.

[bohica2xo]

Full load tests help us look at overall performance, charge level etc. Since you have a non-stock system with a PF condenser & smaller compressor the charge level may need some adjustment.

How does the sight glass look?

[jlutz455]

Unfortunately the new drier doesn't have a sight glass so I can't tell.

[bohica2xo]

It probably does have a sight glass.

Usually they use an adhesive dot like a price sticker over the lens when they paint them. It peels off.

[jlutz455]

Yep , went to the garage and peeled off the sticker painted black. I do have a sight glass, yay! thank you!

Another issue I noticed last night is I'm missing a baffle in the cowl that separates the recirculated air from fresh. So even though the vacuum door is closing on recirculated air, hot air is still getting in the cowl since the baffle is missing. Need to get this piece and see the effect.

Side note, drove my 2013 Explorer to work today to view AC temps inside the truck. Today is rainy and 97% humidity, ambient is 75F deg. with ac on recirc, fan on high driving down highway at 2000 rpm, coldest in the truck is 50F. Fan on low gets down to 38-40F. Seems like humidity has a big effect on cooling because my Explorer is always freezing cold

[Dougflas]

Vent temps may be cooler on low er speeds because the air is contacting the evaporator for a longer period of time thus removing more heat from the air. There becomes a point when this does not happen depending upon the heat load. For testing, we normally use high blower speed 1500 rpm.

[jlutz455]

It was just interesting to get a comparison with a new vehicle to see how the AC performed. I need to hook up my gauges on the Explorer and compare pressures out of curiosity.

Wonder if the low/high side pressures are vehicle dependent of more a function of ambient temps?