1996 tahoe ac problems

[mwj1969]

I have a 1996 tahoe wth front air only ,the problem is my ac only cools down to around 63 to 65 out the vents.

Here is every thing i have done.
1. cleaned evap coil was very dirty –didnt help.
2. evacuated the system put under 28psi vacume for 24hrs—no leaks.
3. recharged with 40oz r134a and 3oz pag oil---no change in temp at vents.
4. blend door is ok..valve that controls heat to heater core off---no heat at core
5. pressure gage when ac is cycling low side 33 to 70. At 33 it cycles off at 70 it cycles on.
6. pressure gage when ac is cycling high side 70 to 100(varies) when cycling is off and 180 to 225 when it cycles on.
7. jumped the low side cutoff switch so compressor would stay running but only got down to 33 never went lower.
8. There is a cutoff switch at the high side output of compressor–unplugged it and system keeps working—didnt jump that connector.
9. measured temp with a Infra Red Thermometer at low side output hose on compressor its aluminum and looks like a (small inline acumilator) then goes into rubber hose that goes into accumilator on firewall (60 to 65)degrees.
Measured temp at firewall top pipe from accumilator going to evap and bottom pipe from evap (65 to 70)degrees on both..

Im not sure what is going on every thing looks fine except temps not cold enough.Is this all im going to get from this system.

On a side note hooked guages to my 1998 s10 4.3l and a 1997 ford ranger and they both cycle just like the tahoe but they go down to 20 on the low side guage before it cycles off and they cycle on very similar to the tahoe but the air at the vents is 52 to 55 degrees.

Could this be a low or high cutoff switch or a weak compressor.

Im up for any suggestions before i have my mechanic look at it....Thanks in advance for any help

 

[SunlitComet]

what was the outside temperature and humidity when you got those numbers?

 

[mwj1969]

today it was 82 with 75% humidty

 

[SunlitComet]

You should have had a little more pressure. perhaps undercharged a bit use the chart below to fine tune.

 

[mwj1969]

could you email me that chart cant read when i print out. thanks
[email protected]

---------- Post added at 10:04 AM ---------- Previous post was at 08:48 AM ----------

thanks for the chart ok here are the #'s
80 degree
50% humidity
2000 rpm
30 low
210 high
64 degree vent temp

looks like low side is ok high side not so good
tried to add a little freon no change

 

[letsbangout]

could you email me that chart cant read when i print out. thanks
[email protected]

You can open the image, right-click, Save it, then email it or do whatever you want with it.

Given that your system only needs 36 oz. for a full charge as per spec, perhaps you have a blockage somewhere. "conventional wisdom" says that if your evaporator input/output pipes vary in temperature by more than a degree, your blockage is in the evaporator. But after observing the same thing on my own truck, with what appears to be a condenser blockage, I wouldn't recommend making any assumptions. Assuming there are no discernible high-side blockages before the orifice tube (which you'd know from a drastic change in temp in one spot along the high side hose before the o-tube), I'd inspect the orifice tube. If it's at all dirty or cloudy, you know you've more than likely got a blockage somewhere. If it's clean as a whistle (doubtful), your compressor could simply be worn out. I know many people who've had the original "belly leak" compressors simply replaced their seals and kept running, on what are now 13 to 16 year old compressors, so it's entirely possible. Hope that helps.

---------- Post added at 12:42 PM ---------- Previous post was at 12:39 PM ----------

thanks for the chart ok here are the #'s
80 degree
50% humidity
2000 rpm
30 low
210 high
64 degree vent temp

looks like low side is ok high side not so good
tried to add a little freon no change

I just read your update. I'm no expert, but I'd be more suspect of the possibility of a weak compressor. At 2000 RPM (isn't the system test supposed to be run at 1500?), your high side should be a little higher methinks.

 

[mwj1969]

Thanks for the info the chart that SunlitComet sent me had had rpm at 2000.this ac seems to cycle way to much just like low freon (but isnt)

my ranger and s10 doesnt cycle like the tahoe and they build high pressure to 300 at 2000 rpm (cold ac)

I was afraid i was going to have to break it apart to start looking for the problem.

is the o tube at the condensor or accumilator on these trucks.

also the hoses on top of the compressor that go to condensor and accumilator are made together with mufflers on both hoses do i need to replace them along with compressor and accumilator or can these hoses be flushed to. and what are the best way to flush without flush gun setup

 

[SunlitComet]

On front a.c. only units the orifice is at the condensor. That 2000 rpm chart is specifically for 1996 reference units.muffler lines can stay but if you flush do it all get a new reciever dryer if you get a compressor. So it is what I am leaning towards. It seems a little too weak.

 

[gpracer1]

Sounds like it is cycling too soon. I thought they cycled at ~28-27?
I would try the cheap $ switch first.
You just unscrew and install. Go from there.

You say when jumped it never got below 33 psi, is that idle or 2k rpms?
If so, could be overcharged or weak compressor.

 

[mwj1969]

Got a cycling switch today will try tommorow
i cant remember but i think it was at idle when i jumped cycle switch plug.

Also there is a high pressure switch on aluminum mounting block on top of compressor and a low pressure switch on back of compressor that i would like to check, how are these switches troubleshooted.

If all my switchs are ok im going on weak compressor theory

question if i break this down and the orfice tube is shot could i just replace and and spend 40 to 50 dollars for it and freon to see if that was the problem or just get a kit with accumilator,compressor and o tube do a good flush for about 150 to 200 on ebay.

also would you go back with ht6 or sanden compressor