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Pressures when ambient temp is 95 to 100

Joeyg on Fri July 10, 2009 2:50 PM User is offline

Year: 1984
Make: Chevrolet
Model: K5 Full Sized Blazer
Engine Size: 350
Refrigerant Type: R134
Country of Origin: United States

I'm about to service my AC on Old Nellie, my trusted old 1984 Chevy K5 Blazer.

I plan replacing the accumulator, orifice tube, hoses and compressor, seals and o-rings. It was originally an R12 system that was converted years ago to R134a by a local shop.

I'm a rooky.

1.) When I'm charging with R134a, what pressures should I be reading with the engine at idle when the outside temperature is at 95 to 100 degrees. I'm located in hot, humid, Houston Texas.

1984 Chev K5 Blazer

TRB on Fri July 10, 2009 6:31 PM User is offlineView users profile

23 - 29 low side

250 to 325 high side.


When considering your next auto A/C purchase, please consider the site that supports you:

Chick on Fri July 10, 2009 6:57 PM User is offlineView users profile

Don't forget to pull a deep vacuum and charge into the vacuum, you didn't mention if you had a vacuum pump, better safe than sorry... Hope this helps.

Email: Chick


Freedoms just another word for nothing left to lose

Joeyg on Sun July 12, 2009 10:10 AM User is offline

It was about 100 degrees when I started charging. I quit with the low pressure reading 39 and the high pressure reading 260. It was recommended that I have a 29 low side and up to 325 high side. Well, I was high on the low side but on the lower end of the high side so I decided to stop. I was reading 81 degrees at the vents with the fan on high and the doors and windows open. The test drive with the windows up and gradually lowering the vent fan speed, it came down to 65 degrees at the vents and was quite comfortable. This morning, with the outside temps at 83 degrees, I was able to get the vent temperature down to 45 degrees. It was quite chilly in Old Nellie. I've owned the 84 K5 Blazer for 25 years and am quite pleased with the outcome. The Hot, muggy Houston climate can be like hell without air.

This is what I did:
I broke the system apart and flushed the evap and condenser and what was left. I then replaced hoses, compressor, accumulator, and orifice tube. Come to find out, the shop that had worked on the system a few years back had put the orifice tube in backwards.

I rented a vacuum pump from Autozone. They charge you 200 bucks, then refund the entire amount when you return it. So the rental is free. I also rented a manifold gauge set because I wanted another yellow charge hose so I could hook up both the R134a cans and the a hose to the vacuum pump thereby not losing any vacuum when I changed from going from vacuum to charging mode.
I pulled a 30hg vacuum, then removed the vacuum hose and waited 45 minutes to see if I had a drop in vacuum.

There was no vacuum drop after 45 minutes so I hooked the vacuum hose back to the manifold gauges and ran the pump for about 2 1/2 hours to try to remove any moisture in the system.

After 2 1/2 hours, I simply removed the yellow hose that the vacuum pump was attached to from the manifold gauges, and closed the high side valve on the manifold gauges.

Then with the can already on the other yellow charge line hooked up, I simply turned the knob to pierce the top of the R134a can and then turned the knob backwards to allow the refrigerant to flow into the system and with the vacuum in the system, it sucked in about 1/2 half of the can of R134a without even starting the engine.

I noticed the 12 oz can of R134a was real cold when I did this, a thin layer if ice formed around the can, it troubled me, but I continued anyway.

I had done some research on the 'net, and one person said he would unplug the low pressure switch, and jump a wire between the two connectors on the harness so the compressor would not stop then engage and stop then engage at the beginning of the charging process.

I ran the jumper, started the vehicle, turned on the ac on high and opened the doors. After I had put two cans of R134a into the system, I removed the jumper and plugged the harness back into the low pressure switch.

I continued to add R134a, and at the last of the 3rd can, like I said, I was reading 39 on the low pressure and 260 on the high pressure side. I was high on the low pressure side but well within the lower limits that was recommended on the high pressure side so I quit.

It seemed to work well and I'm very happy. My old Blazer is......well......just old, and if the AC in her can keep me comfortable during the Houston summers, then I'm a happy camper.

Thanks everyone for your comments.


1984 Chev K5 Blazer

Chick on Sun July 12, 2009 10:49 PM User is offlineView users profile

Check you fan clutch, might pay to replace it then check pressures again, feel the lines going into and out of the evaporator, should be the same temp, with the outlet just slightly cooler, if it is, then you're full... In that kind of heat, air flow is very important, and a weak fan clutch can be hell on cooling... Just a thought...

Email: Chick


Freedoms just another word for nothing left to lose

Joeyg on Mon July 13, 2009 6:53 PM User is offline

Today, riding home from work, I was getting about 60 degrees coming out of the vents, with the fan on high, it was about 101 ambient temperature. Coolant temperature was about 200.

I found some specs on my '84 K5 Blazer and it calls for 3 lbs of R-12. I've read that you should put in 80 to 90% by weight of r134a when retrofitting to a r12 system.

3 lbs of R-12 = 48 ounces.
I got about 35 ounces of r134a in mine when I charged it over the weekend ( see my earlier post ). Should I try to run that up to 38.4 ounces which would be 80% of the R-12 spec or go for just over 43 ounces which would be 90% of the R-12 spec ?

I was at about 260 psi on the high side which from what I was told was the lower end and I could go from 250 to 325 on the high pressure side at 95 to 100 ambient. But on my low pressure side I was at 39 PSI and I was told at 95 to 100 ambient, I should be at 29, so I was high on the low pressure side.

Which kills your system, the high side or low side? I understand it's much more complicated than that, but at what point do you blow the high pressure valve on the compressor or other components.

I'll hook up the manifold gauges again this weekend and verify my pressures again, but I'm thinking it needs just a few more ounces to really get it tuned to the max.

Opinions anyone?

I can live with it today, but it is terribly hot and humid down here, and I still have the rest of July, August, and September to go. If I could reduce my vent temps by even 5 degrees or more, it would help a lot. Old Nellie shakes, rattles, and rolls and they didn't build them with a lot of insulation or anything back then, and it would just be great if I could the ac blowing really cold on a 100 degree day.

Would it help if I wrapped the line coming out of the evap with some insulation, maybe build me a foam insulator around the accumulator and tried to insulate the evap housing on the engine compartment side? I went completely thru the vent system a while back, all of the vacuum doors are opening as they should, and I even sealed all of the connections to the duct system better than factory, so all of that is working well, and probably better than new.

Fan clutch is working fine, I checked it today.

I took the grill out and sprayed down the condenser core, it is pretty darn clean and no leaks, so I don't want to replace it, as I will get a chinese made one that probably would be junk.

I checked the outside of the evap it is clean also.

The inlet to the evap, right after the orifice tube is cool, it is sweating but not freezing up, the tube coming out of the accumulator is a little colder than the evap inlet.

Just thinking I need a few more ounces of R134a. But not sure about the pressures.

1984 Chev K5 Blazer

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