# 2000 Tahoe A/C - front not cold, rear kind of cold



## davescountry (May 8, 2011)

All - 

I had another thread going on a Malibu, and thanks for the help. I am now working on a 2000 Chevy Tahoe. 

Here is what is happening. I have put in about 20 ozs of 134. My pressures are currently reading 42 psi with A/C on, and about 85 psi with A/C off. I know my gauge is pretty cheap - its a $25 interdynamics gauge from O'Reillys. I have been advised that a high/low gauge might be a good investment, but haven't had the chance to find one yet. I will probably pick up another can of 134 and see if I can get pressure closer to 50 psi. 

With the above pressures, my rear A/C seems to be putting out close to 60 degrees at idle. I haven't test driven it yet, so that is after about 5 mins or so. My front vents are putting out about 80 degrees, which is probably about what the outside temperature is right now. 

I will also add that my blower motor controls are kind of touchy. It works on setting 4, and if I wiggle it, setting 3 -- but not 1 or 2. I don't know if I need a new resistor there since it does work on 3 or just what exactly. I can tell that my A/C "on" button, temp control and position settings (defrost, etc) work fine. I should add that with the front vents, there is plenty of volume of air coming out, just not very cold. 

Any ideas on why the front doesn't seem to be blowing cold?


----------



## Midnight Tech (Dec 31, 2001)

That deal with the blower switch sounds like it's going bad. I'd go ahead and replace the switch - the resistor just does what the switch tells it.
Wonder if the front orifice/expansion valve is partially clogged?


----------



## davescountry (May 8, 2011)

Any idea if there is a way to test of the orifice tube is clogged? 

Ordinarily, I'd figure since its never been replaced, its probably old so worth replacing and if it fixes the problem, great, but if it doesn't then at least I have a new part where there was an old one. But, if my understanding of AC systems is correct, I am going to have to discharge the system, replace the tube, draw the system down and then re-charge. 

I don't have the gauges or the vacumn pump for that, and would be hard for me to dump my system, buy the tools, parts and new 134. I'd think that would be at least $150 to $200. Probably cheaper than an A/C shop, but hard to afford unless I am pretty solid this is the problem. So, testing would be nice.


----------



## Wrench97 (May 10, 2008)

That's why you need the high and low side gauges to see what both pressures are, 50 on the low side would be too high, but without knowing what the high side reads..........

Make sure the heater hot water valve(if it has one) is shutting off the flow of coolant to the heater core, if it does not have a hot water valve it'll have a blend door in the heater box to control air flow through the heater core, Vise grips and a rag to block off the heater hose is one way to test for this.


----------



## davescountry (May 8, 2011)

Thanks. I will try and fine a manifold gauge set tomorrow if I can. I live in kind of a small town, so options are sometimes limited without a drive. 

Here is some more info, if it helps. I took it for a test drive this afternoon. It was 85 degrees outside. After about 5 mins, the dash temp dropped to about 70 degrees. The rear air vents were steady at 60 degrees, same temp as at idle. I drove for about 15 mins, then did some shopping. 

When I came back, I drove for about 10 mins with vents on, no A/C and the temp reading was about 90, slightly higher than the outside temp. I just wanted to make sure that the 70 degrees I registered before wasn't a result of just pumping air through. I then drove for about 5 mins, front A/C on, no rear air and after about 5 mins, the temp dropped back to close to 70 degrees. 

Here is the heartbreaking part though. I retested my pressures after the drive. With A/C on, my pressure is now about 28 psi, and with A/C off, about 70 psi. 

So, I appear to have dropped about 14 psi over the course of the drive. Since I am a bit of an optimist, I am hoping this might be the result of a hot engine, or just more circulation through the system, since I know it is a big system due to the rear air. Hoping against all that I don't have a massive leak. 

I do know I have had some leakage around the compressor over the years, becuase of discoloration. I actually washed the engine the other day, so when I looked this afternoon, I did not see or feel any fresh discharge, just could see the discoloration. I have heard a bit of discoloration with this many miles isn't too uncommon. 

So, might be info overload, but just thought I'd throw these thoughts out. I have another can of 134, and not sure if I should put it in.


----------



## Wrench97 (May 10, 2008)

With refrigerant as the pressure is directly related to temp, as the temps go up the pressure goes up, 28 PSI on the low side is around 32 degrees(guess it's printed on the gauge face) in the evaporator in a fully charged system, you want to see a low side in the 40's high side below 225 with the cooling fan on.
The only way to be sure the charge is correct is to evacuate and recharge the system using a scale to measure the amount of refrigerant installed, but you can get close watching the pressures.
With rear systems check the pipes/lines running under the truck to the back often they rust out and leak.


----------

