1995 Buick Roadmaster - Poor Cooling - Pressures

[scoob8000]

It's a bit hotter out today. 88 degrees, and 55% humidity

At 1800rpm I'm seeing 50L/250H with both condenser fans running, control set on max, all windows open. After a short highway drive, the lowest I saw my vent temp drop to was 58 degrees. After getting back home, there was only minimal condensation on the accumulator and barely anything dripping under the car.

I re-did my test of blocking the consensor. I actually pulled both fan fuses. High would maintain around 200psi, at higher RPM it climbed to 350 before I let off. Soon as it returned to idle it dropped back to 200.

[JohnHere]

It's a bit hotter out today. 88 degrees, and 55% humidity
At 1800rpm I'm seeing 50L/250H with both condenser fans running, control set on max, all windows open. After a short highway drive, the lowest I saw my vent temp drop to was 58 degrees. After getting back home, there was only minimal condensation on the accumulator and barely anything dripping under the car.

The pressures and vent temperature are still too high for that ambient temperature and humidity level. Very little condensate is another tip-off that not much is going on cooling-wise.

As far as you know, did anyone else work on the A/C system before you got the car? The reason I ask is because there seems to be an insufficient restriction at the entrance to the evaporator, proper expansion of the refrigerant, and hence the high low-side pressure. It could be that someone somewhere along the line serviced the system and forgot to reinstall the OT, installed one with too-large an orifice, or installed a variable OT that isn't working correctly.

Are the evaporator inlet and outlet tubes about the same temperature (cold)?

I re-did my test of blocking the consensor. I actually pulled both fan fuses. High would maintain around 200psi, at higher RPM it climbed to 350 before I let off. Soon as it returned to idle it dropped back to 200.

If you measured up to 350 PSI under those conditions, then I'd say that your compressor is working okay.

[scoob8000]

I just went out and checked the evap tubes. Both feel about the same. (cool).

I can't really get my fingers on the tube near the condenser where the o-tube goes. I was going to try to see if there was a noticeable temp difference before and after it. The high side at the condenser is HOT after only a few minutes of idling. More hot than you want to touch.

We've had this car for 15 years or so. I've never had the system open, can't speak for the previous owner though. It started out cooling fine, then the wife said it's not as cold. Until I drove it and said no crap, and started digging.

The accumulator still has the original GM sticker on it, not that that means much.

I think my next step is to pull the tube and inspect. Doing a quick image search, variable tubes have the outlet more encased in plastic vs the clear net over the exit. Is that always the case?

[JohnHere]

A few more issues come to mind.

The clutch cycling switch on the accumulator could cause the higher than normal pressures and mediocre vent temps that you're experiencing if the switch is out of spec--that is, if it's not allowing the compressor to cycle on and off at the correct pressures--which is possible on a 26-year-old car. While the system is still fully charged, you can easily change the switch. If memory serves, there's a Schrader valve under it that will prevent loss of the refrigerant.

Is the fan on your LT1 5.7L V8 an electric unit or is it the viscous-drive type? If it's the latter, those fan clutches do wear out over time and can be deceiving. The fan will look like it's spinning okay but might not be able to come up to full speed and power when the condenser needs airflow the most. If it's electric, the motor could be weak, with the same effect on airflow.

Speaking of which, how does the condenser look? Any corrosion that would prevent effective tube-to-fin contact and heat transfer? Any bent fins or hidden dirt embedded between the fins that could obstruct air circulation?

If none of the above solves the problem, another remote possibility is air and moisture in the system. I say remote because it has been professionally evacuated and recharged at least once already. But strange and baffling things can often happen with MVAC systems.

If you do decide to open the system to replace the OT, I would also replace the accumulator at the same time. It has a screen and desiccant beads inside with the latter being contained in a bag. The desiccant bag can become partially plugged with debris, moisture, and oil, or sometimes even break open with the beads scattering throughout the accumulator and obstructing the screen.

Come back and see us and let us know what you find should you decide to get back into it.

[scoob8000]

Thanks. They are electric fans (2 of them).

The condenser looks good. I actually sprayed it down with some purple power and hosed it down in the midst of all this troubleshooting.

I believe you are correct on the pressure switch. We've actually got a couple of these cars. I think my first foray on this forum was when I completely rebuilt a system on one of them many many years ago.

I'll do some digging but will come back with any findings.

[scoob8000]

Pulled the o tube. Not really suprised. It's full of metallic grit. Not black death, but definitely lot of metal.

Gonna fully flush and RR the compressor, tube, and accumulator.

I'll post updates.

[JohnHere]

That's a nasty looking OT, all right. I'm surprised that the low side wasn't pulling into a vacuum with that much debris obstructing it. The question is, where did all that metallic crud come from? The compressor, most likely. If so, it's definitely time to replace it.

You can flush the condenser if it's the tube-and-fin type, along with the evaporator and lines/hoses as long as they don't have any mufflers in them. But I would just replace the OT and the accumulator with new parts. They're cheap, and the accumulator can't be flushed anyway.

Everything that you'll need is available from this site's sponsor, too.

[scoob8000]

Definitely.

I just fought with getting the compressor out. Probably spent 3 hours fighting the bracket on the back. Can't get on the bolts because it's between the frame and block.

It's a HD6 unit. 3 mounting ears on the front, two bolts in the back thru a bracket to the engine block.

Few guys on the one forum for these cars suggest leaving the rear bracket off because it's just that bad. Any concerns with front mounting only?

[Tim]

And they return the compressor for warranty, claiming the front ear broke.

[JohnHere]

You definitely don't want a front mounting ear to break off of a new compressor after going through all the work and expense of repairing, evacuating, and recharging the system. And it won't be covered under warranty, as Tim alluded. Can you jack-up the engine a little bit to gain some clearance for bolt removal? You might have to disconnect the motor mount on that side to do so, although I'm not sure about that.