Before I blow a hose or something lol, lemme get some input.

Summer is upon us here in sunny Florida and we're in triple digits... The AC in the Blazer just isn't up to task to keeping the interior cool it seems.

Here's the specs:

Ambient outside temp: 103
Humidity: 31%

--AT IDLE--
Low side pressure: 45-46
High side pressure: 255-260

--2K RPMs--
Low side pressure: 42-43
High side pressure: 330-335


It doesn't matter if I'm at idle or 2k RPM's, the vent temperature stays at roughly 65 degrees consistently while on fan speed one, and the vent temp only gets worse if I select a higher fan speed. And it doesn't matter if I'm parked (note, I have Intrepid electric fans and this is with then on full speed) or while moving at 45+ mph

I am by no means an AC expert. I'm the guy that some of you might remember about 5 years go replaced the the entire AC system on this Blazer without ever vacuuming the system down, and honestly the system has been doing AWESOME up until this point, not a single issue. But now the time has come to revisit it I'm afraid... Maybe there's just air trapped in the system because of my sloppy backyard fix and a complete vacuum and recharge would do it some good?

Fast forward to now. I have access to a vacuum pump. I have a set of gauges so that I can accurately charge the the system instead of just guessing by charging off the low side and watching a single gauge... I have a spare compressor if it comes down to it sitting in the garage (I work in an salvage yard and they were going to toss it as a core because we didn't need it, it looks like it was JUST installed on the Blazer it was on, it's nearly brand new, so I snagged it). If I need to I will have no hesitation to just go out and get a new orifice tube, accumulator, and some O-rings, and throw this other compressor on if I need to, but if I'm overlooking something else then by all mean's, I'm all ear's...


From what I read, the high side seams to be in the norm for the ambient temp, but the low side seams a bit too low. But I don't want to add freon to bring the low side up and then have the high side shoot up too high...


What's my next move?


Thanks!

 

It’s almost never over 100F here in Florida with humidity in the 30’s. Sounds more like Arizona. I ask because it makes a difference on the pressures. Assuming it’s more like 85-90F then those high side pressures look too high at 2000 rpm. They should be more like 250 psi. The low side pressures are about right. Is the compressor cutting out at 2000 from the high pressure switch opening?Reasons for those pressures and bad system performance could be:

dirty condensor coils (love bugs?)

plugged orifice tube or condensor coils

noncondensables in the system (air or moisture or both)

if the system was not vacuumed then moisture may have reacted with the refrigerant oil and caused a slime to start plugging the orifice or condensor. You would see that when you remove the orifice tube.

btw, if you do pull a vacuum, make sure it holds at 500 microns for 15 min with the pump off. A dirty system can take a while to get dry. You might even need to sweep it with nitrogen between vacuum attempts. Then you break the vacuum with 134a and charge to the nameplate refrigerant weight.

George

 

Trust me, I wish it wasn't actually 103 lol





Condenser is clean, I did check that.

Orifice tube did cross my mind...

 

Is the compressor running full time or cycling with a 65F vent temp? Is the low pressure side cold and sweaty at the accumulator?

George

 

Well I believe I got to the bottom of the issue. Looks like the compressor was in the middle of taring itself apart from the inside and the orifice tube was partially blocked up. I also think there was WAAAAAY too much oil in the system. I bet there was 12-14 ounces of oil in the old drier when I removed it alone. I'm sure that wasn't helping cooling performance...

So over the past few days I've sucked the freon out at work, got a new drier and orifice tube and seal kit, and today I picked up a couple cans of flush and flushed out the evaporator and the condenser and the lines, and then bolted on the spare compressor I've had stowed away in the garage for a couple years now just in case something like this were to happen (now I've got to restock my "warehouse" lol). I'm literally typing this up on the shop computer while I wait on the vac test. That's right. I borrowed a buddy's vacuum pump, and by golly I'm doing it right this time gosh darnit lol.

Got about another 10 minutes to go, so far it's holding vacuum strong, and then I'm going to run the pump for 45-60 minutes while I eat dinner, then come back out and charge the system with freon and see if I can get some cold air!

 

Air in an hvac system always parks in one spot: the top of the condenser coil. This decreases the surface area of the coil and raises the high side pressure. Moisture in an hvac system will usually do one of two things (or both): mix with the oil which then starts to form an acid; and/or freeze as it passes thru the metering device thus causing the low side pressure to drop. Some systems come with a filter drier filled with desiccant which can remove moisture but only in very small amounts.A deep vacuum (500 microns or less) cannot be seen on a manifold gauge which measures inches of water column. If you want to confirm no leaks with a set of manifold gauges then you'll want to let it set in a vacuum for a few hours.

 

Well after the vacuum pump ran for the 45 minutes, the vacuum in the system dropped down to just below the 30 tick mark. I closed the valves and shut off the pump and I let it set there and the system held that vacuum level for a little over an hour and didn't budge, so I was satisfied with that result.

I shot some r134 in her, getting the pressures where the need to be (was dark and the outside temp had dropped, so I'm going to check again tomorrow afternoon when it's still 100 out and see how it's looking), and I'll be darned if she's not cold again! Ambient temp about 87-88 degrees at the time (yes that's "cooling off" here in Florida this time of the year lol). When I got in the truck to leave work today, the same gauge read 120... NOT TOMORROW GENTLEMEN!