# Thoughts on these A/C numbers **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [June 24, 2024, 12:13pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215 "2024-06-24T12:13:00Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![TwinTurbo](https://avatars.discourse-cdn.com/v4/letter/t/8baadc/32.png) [@TwinTurbo](https://community.cartalk.com/u/TwinTurbo)\ **Post date:** [June 24, 2024, 12:13pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/1 "2024-06-24T12:13:00Z")
What do you think is going on here? 2008 Trailblazer 4.2L 4WD LT 158k Original A/C components I noticed A/C acting intermittently at times. Gets much worse at higher ambient temps. Primarily cuts out on Expressway for 10 minutes or more and then seems to recover for another 5-10 minutes before repeating. When it runs, it is cooling decently. Figured evaporator was icing up or perhaps some type of heat soak issue with clutch or switches. Yesterday, I took these measurements in the driveway: ![Capture](https://global.discourse-cdn.com/cartalk/original/3X/6/8/6885d2b5907772abea744bd147460b254fd4728b.jpeg) You can read pressure charts all day and get different normal pressures. The high side seems low at idle. The low side seems OK at idle but drops to the threshold for the switch at engine RPMs you’d expect on the highway… Thoughts? ---
**Author:** ![tcmichnorth](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tcmichnorth/32/25126_2.png) [@tcmichnorth](https://community.cartalk.com/u/tcmichnorth)\ **Post date:** [June 24, 2024, 1:22pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/2 "2024-06-24T13:22:24Z")
My thoughts are evaporator is freezing by symptoms. The pressure readings also indicated the expansion valve needs replaced. ---
**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\ **Post date:** [June 24, 2024, 2:08pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/3 "2024-06-24T14:08:04Z")
And the freon might be a bit low. ---
**Author:** ![asemaster](https://avatars.discourse-cdn.com/v4/letter/a/5f9b8f/32.png) [@asemaster](https://community.cartalk.com/u/asemaster)\ **Post date:** [June 24, 2024, 2:48pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/4 "2024-06-24T14:48:33Z")
First thing I would do is take some scan tool readings and see if the pressure sensors in the A/C system for both the PCM and HVAC system appear to be correct (match the actual values). Then, with the system stabilized at 1500 RPM I would add refrigerant an ounce at a time to see if I could get the low side up a few psi without significantly raising the high side. I think the system is a bit undercharged. ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [June 24, 2024, 2:49pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/5 "2024-06-24T14:49:24Z")
You need to recover the old freon to know how much it has in it… I would do a recover, pull a vacuum and charge with known, correct amount of freon and see how it does… Almost looks like the desiccant bag maybe slowing the flow (moister in the system), causing a slight blockage… that could be the reason when high side goes to high and low side to low at 1500 rpms over the idle numbers… EDIT: Live data probably a good idea too… lol (didn’t think about that) thanks asemaster ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [June 24, 2024, 3:02pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/6 "2024-06-24T15:02:30Z")
It appears the orifice tube is restricted. ![hq720](https://global.discourse-cdn.com/cartalk/original/3X/5/c/5c55278febed4aad3a85027c055b5819ce5aa6a3.jpeg) Tester ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [June 24, 2024, 10:57pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/7 "2024-06-24T22:57:20Z")
My pin-head diy’er thinking is to first make sure the condenser’s cooling fan is spinning when it should, and that the evaporator’s drain hole is open and draining freely. ---
**Author:** ![TwinTurbo](https://avatars.discourse-cdn.com/v4/letter/t/8baadc/32.png) [@TwinTurbo](https://community.cartalk.com/u/TwinTurbo)\ **Post date:** [June 25, 2024, 2:59pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/8 "2024-06-25T14:59:47Z")
First, let me thank you for taking the time to respond with your expertise and insights. Given the age of the system, I am concerned if it turns out to be a partially plugged orifice tube. That would require a lot more time and cost- perhaps too much cost to make it economically feasible for this older truck. Although the point of recovering and measuring the actual amount of refrigerant in the system now is probably the best course of action, I am going to try and see if I can get the low number up above the switch threshold at normal cruising RPMs. Of course, being careful to not overfill it. If that works, great. Otherwise, I will evacuate the system and pull the orifice tube to see if the compressor is failing internally and plugging up the orifice screens… ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [June 25, 2024, 3:14pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/9 "2024-06-25T15:14:37Z")
Make sure to replace the accumulator when/if you replace the orifice tube, I’m sure that desiccant bag is swollen from all the years… ---
**Author:** ![glasspilot](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/glasspilot/32/27886_2.png) [@glasspilot](https://community.cartalk.com/u/glasspilot)\ **Post date:** [June 25, 2024, 3:16pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/10 "2024-06-25T15:16:22Z")
> [@davesmopar](#): > > You need to recover the old freon to know how much it has in it… > I would do a recover, pull a vacuum and charge with known, correct amount of freon and see how it does… That’s the hard way to do it. I know some pro’s who would just hook up their gauges. They could tell from the pressures if it was low on refrigerant. ---
**Author:** ![TwinTurbo](https://avatars.discourse-cdn.com/v4/letter/t/8baadc/32.png) [@TwinTurbo](https://community.cartalk.com/u/TwinTurbo)\ **Post date:** [June 25, 2024, 3:16pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/11 "2024-06-25T15:16:33Z")
I should have mentioned I planned to do that. It’s actually not that expensive an assembly either considering it has the attached hose. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [June 25, 2024, 3:20pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/12 "2024-06-25T15:20:12Z")
If you find the orifice looks like the image I provided, this what will be required if you want to get the AC working again. ![kitcollage](https://global.discourse-cdn.com/cartalk/original/3X/c/2/c220ae36f02a643b2a27a1e446c2b007369561a1.jpeg) Plus you’ll need to flush out the hoses and evaporator. ![51Wiv5HsrKL](https://global.discourse-cdn.com/cartalk/original/3X/3/a/3addddf03cf983e5d82c468042176ed56c383439.jpeg) Tester ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [June 25, 2024, 3:20pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/13 "2024-06-25T15:20:37Z")
Check out Napa new TEM AC kits, around $400 and I don’t remember having any issues with them… 3Y/36K warranty… ---
**Author:** ![TwinTurbo](https://avatars.discourse-cdn.com/v4/letter/t/8baadc/32.png) [@TwinTurbo](https://community.cartalk.com/u/TwinTurbo)\ **Post date:** [June 25, 2024, 3:22pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/14 "2024-06-25T15:22:07Z")
That is my fear. 😉 I’ve been delaying the inevitable and limping along with this truck but if this needs a complete system and cleaning, time to go truck shopping… ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [June 25, 2024, 3:30pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/15 "2024-06-25T15:30:30Z")
> [@glasspilot](#): > > That’s the hard way to do it. I know some pro’s who would just hook up their gauges. They could tell from the pressures if it was low on refrigerant. If you are a shop with a machine, it is easy and you can do it while working on something else… But if not or DIY, I agree you can just use gauges… But with the info shown on the killer spread sheet (props T.T.) the head pressure should be about 204psi, with the head pressure jumping to 245psi and low side down to 20 psi, that is not showing low, that is showing a restriction… now the idle pressures at 40 psi and 150 shows low and or a week compressor… imo anyway… I also normally see AC off pressures about 110psi each… so the 90/90 looks low to me in my area… ---
**Author:** ![cigroller](https://avatars.discourse-cdn.com/v4/letter/c/c68b51/32.png) [@cigroller](https://community.cartalk.com/u/cigroller)\ **Post date:** [June 25, 2024, 3:41pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/16 "2024-06-25T15:41:57Z")
> [@davesmopar](#): > > I also normally see AC off pressures about 110psi each… so the 90/90 looks low to me in my area… Isn’t that just temp dependent? 79/79, if refrig levels are good, suggests it was somewhere around 75F ambient air temp to start. The 90/90 likely b/c everything was just heated up from running the truck. Or am I off base there? ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [June 25, 2024, 4:05pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/17 "2024-06-25T16:05:25Z")
Good point, I am used to high humidity and temps 85+ when doing AC work… Don’t do much when the temps are in the 70’sF… So if that is the case, then it should be (close to) full… Again, that is why knowing how much is in it helps… ---
**Author:** ![cigroller](https://avatars.discourse-cdn.com/v4/letter/c/c68b51/32.png) [@cigroller](https://community.cartalk.com/u/cigroller)\ **Post date:** [June 25, 2024, 6:26pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/18 "2024-06-25T18:26:28Z")
> [@davesmopar](#): > > Don’t do much when the temps are in the 70’sF… Which makes perfect sense! @TwinTurbo, _[edit…forget it. Tester pointed out below where I missed your recording of the air temps at 77F]_ Here’s a temp/pressure chart - just static system. (Just a quick web grab). ![image](https://global.discourse-cdn.com/cartalk/original/3X/7/f/7fa239b1ce3b110b9b03a8099b1a48ad9d414cbd.jpeg) ---
**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\ **Post date:** [June 25, 2024, 6:30pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/19 "2024-06-25T18:30:32Z")
> [@TwinTurbo](#): > > if this needs a complete system and cleaning, time to go truck shopping… Then maybe put in a bit of freon and see how it does. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [June 25, 2024, 6:40pm UTC](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215/20 "2024-06-25T18:40:21Z")
> [@cigroller](#): > > do you recall about what the ambient air temps were when you collected those data? ![CHART](https://global.discourse-cdn.com/cartalk/original/3X/8/8/8860b07884aa778c54ce438baa043bceb84c4ab7.jpeg) Tester [Next page](https://community.cartalk.com/t/thoughts-on-these-a-c-numbers/195215.md?page=2)