Automotive Air Conditioning Information Forum (Archives)

cris2004 on Sun May 01, 2011 2:01 PM

Year: 1998
Make: GMC
Model: Suburban K1500
Engine Size: 5.7
Refrigerant Type: R134
Ambient Temp: 80
Pressure Low: 35
Pressure High: 150
Country of Origin: United States

Hello, thanks to all who may offer help.

I've put in a new Delco compressor, oriface tube, rear expansion valve and dryer. I pulled out the condensor, it did not seem to have any restriction. Same for all the lines, low muffler is cool, high muffler hot.

At idle I get 42/150, at 1800rpm 30-32/155, this at 80 degrees. Vent temp 70.

The truck cooled great (30/290, 40 degree vent) before sitting a couple months, then I had similar problems. I thought the compressor or clutch was weak, so I replaced it, and subsequently the other work
I did have a few black specs on the O-Tube. I've had the truck since new and never a complete compressor failure

There is so slight a difference in the high pressure at low and high RPM's, I'm wondering if there is a pressure controlling device outside of the high and low cut -off switches. There is the pressure valve in the back of the compressor, one that gets moved into the new one, but I understand it's another emergency relief.

None of my books have this low side -normal / High side low scenario.

Is there only the one oriface tube? I've seen two posted, the rear has an expansion valve.

Anyone have an idea what I am missing or have done wrong?

Thanks very much!
Chris

GM Tech on Sun May 01, 2011 3:56 PM

You have one orifice tube in any a/c system-- if you have rear air, it is located just beyond "Y" split, if front air only- it is in condenser outlet pipe. The rear evap uses a TXV.

Unfortunately, people and mechanics get confused and forget to check the condenser outlet pipe when installing a new condenser- many time the condenser has an OT already in it- which is fine if you have a front air system only. But if you have front and rear air, then you have the 2 orifice tube scenario--which is a mistake. seen it many times- condenser pressures are wrong- also if plumbed backwards - condenser cannot do its job and pressures are wrong again- can't build enough head pressure- because no liquid gets to OT, only gas goes through it- I've seen it a dozen times or more on C/K trucks- usually from body shops who replace the condenser after a deer strike.

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Edited: Sun May 01, 2011 at 4:06 PM by GM Tech

cris2004 on Sun May 01, 2011 11:15 PM

Thanks. I didn't think it had two but was told it may. I can see where the confusion comes from now. I pretty much stick to arrows for my deer lol.
My condensor is plumbed correctly, is the original one with no oriface tube. The system was fine until sitting a couple months when these symptoms cames up.

GM Tech on Mon May 02, 2011 4:07 AM

How are you charging? weighing it in? cans? vacuum? proper amunt of refrigerant is crucial......

are you sure yor gage set doesn't have blow-by in it?-- high low and low high looks like a partial bypass, either through gage set or rear air loop- perhaps rear TXV is stuck open-- (try pinching off rubber liquid line at rear (under truck) to prove/disprove rear TXV bypass- I use a huge c-clamp) for gage set, just hook up one side at a time, to test it out.

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Edited: Mon May 02, 2011 at 4:07 AM by GM Tech

cris2004 on Mon May 02, 2011 6:48 PM

I vacuumed it out several hours to -28, letting it sit over night to check for a leak. I use a bulk tank on a commercial digital scale. I could be off a wee bit but it's pretty good. I went 1/4 over to see if the high side would pick up, but it did not, while the low side did.
I'm confident the gauges work allright, I haven't had any problems with readings on two other cars I've had to tinker with this week. None the less I will check individually.
The TXV is new, I changed it after having this problem still after the first attempt. It's an all steel or aluminum line from the condenser to the rear or I'd give that a shot too.