Automotive Air Conditioning Information Forum (Archives)

Provided by

We've updated our forums!
Click here to visit the new forum

Archive Home

Search Auto AC Forum Archives

what are proper recharge psi at different temp/rpm 87 cadillac devile

willpower101 on Thu August 23, 2007 3:59 PM User is offline

Year: 1897
Make: cadillac
Model: deville
Engine Size: 4.7?
Refrigerant Type: r134a
Ambient Temp: 100
Pressure Low: 30-42
Pressure High: 325-200
Country of Origin: United States

This system was ICE cold two years ago. (In fact, when I opened the hood I was really surprised to see an r134a conversion) Then the computer keep killing the ac system and throwing a low refrigerant code.

The ac was blowing warm. I attached the good style gauges a few days ago and put about a 1.5-2 cans in the system 3 days ago.
It was 10pm, temp 85, humid 60%.
Car idles roughly 1800 rpms on idle because of a throttle control module problem. (I can manually make it run lower when needed) I have no tach to rpm's are a guess.
I was targeting 30 psi low side and 230 high side. NO matter how much I shook the can and bursted the system seemed to be completely filled at 28psi low and 240 high. After revving the engine up to (again just a guess) 3000rpm and holding, it would decrease to abotu 24 psi low side and 270 high. (these are close estimates from memory.)
Temps in the vent ran 48-53 degrees with in car ambient temps around 65.

3 Days later. It doesn't appear to have any significant leaks. (black light dye)
2pm, outside temp 100, humidity 31%, vents cool at around 55 degrees, putting in car ambient temps at about 75 degrees.
I pulled in after a drive and took some readings, this is what I got.

Pressures in psi:
Low / high
95 / 110 After connect without engine on
42 / 200 At a low idle 800-1200 rpm
45 / 275 At low idle after running for about 60-120 seconds
39 / 250 Roughly 2500 rpm (guess) for 30 seconds
30 / 325 Roughly 2500 rpm after 60 seconds

Something seems wrong, but I'm not sure what. My first guess is that I need to take out enough refrigerant to get it run about 30 psi's on 800-1200 idle. But what pressure will it be on acceleration if I do this? (am I tryign to avoid having it cut off at 20?) (also, the fact that it seemed full the other day when it was idling high, makes me think i've overfilled it.)

Edited: Thu August 23, 2007 at 4:00 PM by willpower101

willpower101 on Thu August 23, 2007 4:58 PM User is offline

ok, well, i'm pretty sure I found my own answer. Using a digital thermometer at the center vent this is what I found.

58 @ true idle of 800-1200
54 @ high idle (esitmated 1800 rpm) when tcm get's outta wack
47 @ approximately 3000 rpms (holding down the peddel a third of the way like I would be accelerating)

It seems that the high idle probably threw my original measurements off and I assume I should let some refrigerant out until it's 30psi @ 800 rpm.

Chick on Thu August 23, 2007 5:22 PM User is offlineView users profile

What you should do is recover the refrigerant, pull the O tube out and inspect it, and of course change it. Use the Ford "blue" O tube, find and fix any leaks, then pull a deep vacuum and recharge into the vacuum about 80% of the R12 charge and tweak it from there.. You'll have ice cold air.. If the O tube is black or clogged, you may have other issues..But if it's clean, the recharge will put it back to very cold..Hope this helps..
Vac/charge procedures

Email: Chick


Freedoms just another word for nothing left to lose

iceman2555 on Fri August 24, 2007 10:00 AM User is offlineView users profile

I do not understand the idea of a 'target' pressure. The system must be filled to specific quantities for proper operation. With an ambient temp of 85/100, humidity of 60+% a 30/230 pressure equates to an undercharged system. It should be that the system is fully charged first....test pressures second. Pressures are not always indicative of a fully charged system. Esp with retro'd vehicles. Caddys' are one of the worst. Throw out the 70-whatever % of 134a to 12 specs. Charge until the inlet and outlet of the evap are the same temp. Max Cool...High Blower....Doors Open....Engine @ Idle. Highest heat load on the evap. When this occurs the system is fully charged. All is well......except......a possible high side pressure or a perceived high side pressure problem. If excessive pressures are not remove refrigerant...this may lower pressures and may even produce a slightly lower vent temp....but the compressor will surely suffer from lack of lubricant. Insure that engine cooling is fully operational....esp air flow across the condenser.
Follow Chicks advice....get it all out.....recover...although not a fan of the blue orifice thing.....if needed go for the yellow GM a bit smaller orifice than the Ford unit but do what you think best. Evac and recharge....test at idle....for operations and then at elevated engine speeds. If a system will operate and cool at will operate and cool at elevated (highway) speeds. The greatest heat load occurs at stop lights....not at 75mph.
Good luck!!!

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

NickD on Fri August 24, 2007 2:36 PM User is offline

If you have to add that much refrigerant, still have a leak, are these cars using the single lip compressor seal? Those aren't easy to find with dye.

But when it kicks into Econ, you are low, on the 2-6 psi low side, have to find that leak first.

Seems to me if this system was working for two years without the AC light coming on, could have been a proper conversion, it's when the conversion is first made and the guy is going nuts with the check AC lamp that the orifice or low thermistor resistor trick has got to be used.

I charge with gauges, also lots of hand feeling, weighing, and listening, am I being naughty? More information, the better. Finding that point where the evaporator temperature stabilizes with increased charge pretty well defines the point, also looking at the gauges to see if those are in the ballpark and peeking at the high side plus feeling for condenser cooling problems.

Dave in Texas on Sat August 25, 2007 10:06 PM User is offlineView users profile

Willpower....have similar vehicle with similar problems. I used the OEM GM orfice tube when I converted back in '98, so I'm pretty sure the tube is dirty/strangled. I intend to install the Ford tube when the time comes. 4.1L engine Email if you care to.

At 2, I went home with a 10. At 10 I woke up with a 2 !!

Back to Automotive Air Conditioning Forum

We've updated our forums!
Click here to visit the new forum

Archive Home

Copyright © 2016 Arizona Mobile Air Inc.