1995 Buick Lesabre

[Mark86]

I expected to see HS pressures in the 250 psi range with the high ambient temps and 30-35 on the LP side.

I have a relay test cube, I’ll toss that in and turn it on and see what speed it drives the fans. I actually have a set of fans for this car, that came out of a low mileage wrecked car. It would not surprise me if the fans were on the tired side. The electric motors sit about 2” from an exhaust manifold. They have heat shields, but tough environment.

[DetroitAC]

You are getting high side pressure of 215 psi in Arizona, your condenser isn't the problem. Plenty of vehicles would be thrilled with that.

If you really want the high side to be 250, start blocking it off with duct tape, shopping bags, dead birds, whatever, it's easy.

[tbirdtbird]

Except that his pressures dropped with misting. Easy enough to max out the fans and see what happens, then go from there

[DetroitAC]

How could the condensing pressure NOT drop when you mist the condenser with water? It's a better heat transfer fluid and it's colder. All I read from that result is "yep, thermodynamics works just my textbook said it does".

the airside of any vehicle's condenser can be made better, but that isn't where this gentleman's problems are. 215 psi is a win, depart the field with your victory.

The low side isn't low enough to blow cold air, that's where the problem is. Condenser pressure is a bit low for Arizona because the system isn't rejecting much thermal power. If you can fix the issue and get it to perform well, condenser pressure will go up.

[Mark86]

That was my thought train. Weak pump puts out low pressure and corresponding higher vacuum. Commercial/stationary Ac units use water over condenser for just that added efficiency. In Phoenix one would always see a response with water misting as the evaporative process is near instantaneous.

Tossed my test cube relay in, forced fans to max. Drove the car to work (45 min drive) mostly freeway, and 10 min in town driving, saw better duct temps, but the ambient was 10* cooler today vs yesterday, still a delta of 50* duct vs outside air temp.

I’ll order up a pump.

[JohnHere]

If you really want the high side to be 250, start blocking it off with duct tape, shopping bags, dead birds, whatever, it's easy.

Good one

[Mark86]

Ok, new Denso compressor installed. Put in the amount of oil that came out of the old compressor. Sucked her down and filled with 30oz liquid 134a. Started the engine and turned on the A/C. It was ice cold but short cycling due to low charge. I walked the last 9oz in as a gas. The accumulator was very cold, and dripping wet which is unusual for phoenix.

Ambient temp in my garage 99*
Engine idle 600 rpm
LP = 49 HP = 225 vent temp 65*
Spritzed with water
LP = 45 HP = 200

Engine RPM 1300
LP = 35 HP = 255 Vent temp 53*
Spritzed with water
LP = 32 HP = 230

[JohnHere]

We're not concerned with the pressure and temperature readings at idle because the compressor isn't really doing much of anything at such a low RPM. 1,500 to 1,800 RPM is the typical RPM test range that professional shops use.

Did you have a chance to take it for a drive on I-101, I-17, or I-10 so that you can build some speed (at least during non-rush-hour times) and maximize airflow through the condenser? I would bet that the vent temperatures would drop into the mid-40°F range under such conditions even with an ambient temperature of around 100°F.

[Mark86]

Did errands today, light town and county roads. OAT was 111 and a duct temp of 53 after a mile cruise at 55 mph. A 58* drop. Idling in drive duct temp would climb to 60-62. Much better then before.

I understand the high rpm test but my weak compressor was doing so little at idle/low RPM it made the ac all but unusable unless on the highway at 75 for 30 min. 50 mph in O/D is 1500 rpm. Let off the gas to coast, torque converter unlocks and rpm falls to 1100. Driving around in 3rd would help but that’s just masking the short comings of a weak pump.

[JohnHere]

Ambient temp in my garage 99*
( ... )
Engine RPM 1300
LP = 35 HP = 255 Vent temp 53*
( ... )

Although the HP looks good at that ambient and engine speed, the LP of 35 PSI corresponds to an evaporator temperature of about 40°F—not that great to provide adequate cooling in the extreme heat of the Southwest. I don't recall, but have you tested the pressures at 1,800 RPM to see what the low side is then? It would be nice to get the low side down to 30 PSI, or about a 35°F evaporator temperature. I'm pretty sure that would bring down the vent temps into the 40's.

Did errands today, light town and county roads. OAT was 111 and a duct temp of 53 after a mile cruise at 55 mph. A 58* drop. Idling in drive duct temp would climb to 60-62. Much better then before.

Did you feel comfortable at those vent temperatures?