Charging 2002 Blazer AC

[reefgeorge]

I let you know how it works out. Thanks.

[reefgeorge]

I picked up more information from an AC tech that worked for a GM dealership and has worked on thousands of GM systems over a long time period.

GM has at least 3 different types of AC systems. One of them is a CCOT system but it is used in a small number of luxury models such as Cadillac’s. The 2002 Blazer can have 1 of 2 of these versions (neither CCOP). You cannot describe the function of my system unless you first ask if I have manual controls or digital controls. I have manual.

System 1, manual controls:

There is a high pressure and a low pressure pressure switch in the refrigerant circuit. High pressure for severely out of bounds conditions for protection. Low pressure to protect at the limits of operation (cold ambient, low cabin load, etc.), or for out of bounds conditions (very low on 134a, etc.). This system regulates cabin temp by using a blend door to mix cold from an all out compressor/evaporator, with heat. There are no thermistors and the compressor is not designed cycle under most conditions. At the target conditions for testing (1500 rpm, max blower, and high cabin load) the compressor does not cycle and you can get steady state readings.

System 2, digital controls, no CCOP (found as an option on the 2002 Blazer)

Besides the pressures switches there is temperature sensing and a digital control head. This system also will not cycle at high initial loads but rather will run all out until you approach the target cabin temp and then will cycle the compressor all on and all off with a fairly wide range (+/- 8F). The evap coil still heads towards near freezing while on.

System 3, CCOP - not found in the Blazer:

System 2 plus additional temp sensors, line temp sensors for the refrigerant, and a more elaborate cycling algorithm. This system will cycle often because it attempts to control the cabin temp to within +/- 2F and cycles the compressor in such a way that as you approach the cabin target, the evap temp is much closer to the cabin temp than a normal system will produce. If say you are near your cabin temp target of 75 F, the evaporator may be held to 65 F through cycling to provide better cabin comfort.

[old_master]

Originally Posted by reefgeorge

....The 2002 Blazer can have 1 of 2 of these versions (neither CCOP). You cannot describe the function of my system unless you first ask if I have manual controls or digital controls. I have manual.

From the excellent details and descriptions in all of your posts, especially the first one, I was pretty sure you had manual AC. The CCOT refers to the general type of refrigerant system: Clutch Cycling Orifice Tube = The clutch cycles and refrigerant metering is done with a fixed orifice tube.

Originally Posted by reefgeorge

System 1, manual controls:

There is a high pressure and a low pressure pressure switch in the refrigerant circuit. High pressure for severely out of bounds conditions for protection. Low pressure to protect at the limits of operation (cold ambient, low cabin load, etc.), or for out of bounds conditions (very low on 134a, etc.). This system regulates cabin temp by using a blend door to mix cold from an all out compressor/evaporator, with heat. There are no thermistors and the compressor is not designed cycle under most conditions. At the target conditions for testing (1500 rpm, max blower, and high cabin load) the compressor does not cycle and you can get steady state readings..

This corresponds with the information I gave you. The "high cabin load" refers to high interior temperature and high humidity; A couple of posts back, I mentioned the "charts" that are in the manual, they show how cycle time changes with temperature and humidity. ie. at 70F and above, and humidity at 70% or more, the clutch is engaged continuously.

The high pressure switch is on the rear of the compressor, the switch contacts are normally closed. If head pressure rises above a predetermined pressure, (somewhere upwards of 367psi) the switch contacts open, which prevents the clutch from engaging. If low side pressure is below 42psi, the cycling switch will not engage the clutch.

Did your shop manual arrive? Does it answer your questions?

[reefgeorge]

No manuals yet althought they have shipped.

I was re-reading my post and it comes off sounding a little strong and was not meant to. I should have said "one cannot describe the function of some systems until the control type is discussed" instead of you...

It was an info dump that I posted on a couple of sites to "give back" but on this one it sounds like I am calling you out. I always appreciate the help.

All my parts are now in and I'll get on this system Sunday and will post back.

Thanks,

George

[old_master]

No problem George, I understand. Keep us posted on how it goes.

[reefgeorge]

Got my GM shop manuals and they confirm that I have a manual, non-cycling AC system. I am waiting for a few more parts and then I will tackle this repair.