AC Not Getting Cold

[josh454]

Hi all,

Having issues getting cold air on my 86 Squarebody truck. Hoping someone with more knowledge assist.

So far I have replaced:
Compressor with a Sanden SD7H15 Compressor
Replaced the condenser with an aftermarket OE replacement
Replaced the Evaporator with an aftermarket OE replacement
Replaced the accumulator with Genuine GM part
Replaced the Orifice tube with the white ACDelco replacement (Twice, first time I put it in backwards)
According to my 86 GM repair manual it should take 56oz of R12. I initially charged 36 and could tell it wasn't cold so I went to 48oz with little change to the vent temps. (Didn't measure it but felt extremely similar)

85 Degree day with 45% humidity I'm getting 68 Degrees out of the center vent on Max AC with recirc on. Feels cool but not cold at all - driving down the road doesn't feel like it changes much, maybe a little bit.

Pressures with 48 oz and 85 ambient temps:
Static pressure is 109 on both sides. (Compared to my 2008 Suburban it was 105)
800 RPMs I'm getting 155/30
1500 RPOMs I'm getting 180/25
Low side kicks off about 23 PSI

Measuring the evaporator at one of the tubes I'm getting 47 degrees. I'm getting pretty close to 32 degrees on the tubes before and after the evaporator. High side line going into the condenser I'm getting 118 and after I'm getting 92. I have dual SPAL 14" fans running on high with an aftermarket Cold Case heavy duty radiator.

I noticed the accumulator starts to freeze about 26 PSI and back to about 4" in front of the compressor.

One of the things I'm confused about is how the Evaporator line can be ice cold but the tubes in the actual evaporator are only 47 degrees. Totally confused at this point wondering if maybe the output of the Sanden SD7H15 doesn't match the orifice tube size? Any other ideas? Appreciate the help, at my wits end on this one!

Thanks,
Josh

 

[fast 99]

How about the heater door not in the correct position, broken or leaking? Try pinching off one heater hose see if there is improvement. Although high side pressures aren't excessively high does the clutch fan work?

 

[YakkoWarner]

I'd second the idea of checking the heater door. If you're freezing up on the evap line but barely anything cool coming out the vents it sounds like you're trying to cool down heated air. Super easy way to test this theory: Turn on the A/C as soon as you start the truck (before the coolant has a chance to get hot). Do you get good cool air that slowly gets warmer as the engine warms up?

I was planning on bypassing my heater core for the summer, but since the rest of my system seems to be struggling now, I'm going to leave it be for now until I can spring for at least a new crossflow condensor, orifice tube and accummulator/dryer.

 

[josh454]

Appreciate the responses - I just put a block off valve on the heater core hose. Made a small difference but is still not blowing cold. I'm going to take the cover off the evaporator housing and inspect for leaks and get temps at the evaporator core. Will post with the results!

 

[Chevy 88]

This may have already been covered, but is the pump running constantly? Intermittently? Infrequently?

 

[SquareRoot]

Compressor.

 

[75gmck25]

Usual recommendation for R134a charge is about 75-80% of the R12 charge, so you are in the ballpark. It’s also usually recommended to use the Ford blue orifice instead of the GM white, since it usually helps cool better.

Your high pressure sounds a little low for 85 degrees, but I’m not sure you could fix it by just adding more refrigerant. Normal is estimated as about 2.2-2.5 times the ambient temperature, so at 85 degrees it would be 187-213.

Did you vacuum it down for at least 30 minutes before recharging?

 

[edgephoto]

Based on those pressures you should have ice cold air. I would look at the heater box and make sure you put foam around the evaporator to seal it to the box. If not air will bypass the evaporator. The high side is not too low based on my experience. MI has a similar climate to CT.

You can see by the chart that 30 psi is 35 deg F.

You want to reduce the refrigerant charge by 10-15% which puts you at 48-50 ounces. You are good with your charge. This is important as the refrigeration cycle depends on the correct amount. Too much or too little causes problems.

When you drove it were you going at least 25+ MPH? A/C depends on good airflow and you stated above you don't have a stock fan but rather you have electric fans. Electric fans don't move as much air as a mechanical fan, despite the claims by the sellers.

When you installed the compressor did you drain the oil out that it was shipped with and add fresh PAG oil in the correct amount. Too much oil is not good either.

I would not worry about ice on the outside of components. That is not unusual. How are you measuring temps under the hood? Laser thermometer? If so, those are not very accurate in my experience. I have a cheap Chinese one, and a Fluke high dollar one and they both give readings that are not accurate.

Post a video with the A/C on and the engine at like 1500RPM. Ideally we can see the gauges and A/C clutch. This will help.

 

[josh454]

Ok finally found the problem on this one guys. There is supposed to be a metal baffle inside the evaporator housing that seals the back of the evaporator core and the firewall. Turns out that is missing allowing the air to bypass the evaporator core between the firewall. I'll get another housing and I think I should be golden. Thank you all very much for the help!

 

[Ricko1966]

Appreciate the responses - I just put a block off valve on the heater core hose. Made a small difference but is still not blowing cold. I'm going to take the cover off the evaporator housing and inspect for leaks and get temps at the evaporator core. Will post with the results!

Blocking the flow through the heater core causes some cylinders to overheat,on some engines,because it is using that path as a bypass. Not saying yours does,I don't even know what engine you have for sure. But look at a lot of factory heater core valves I think a 99 escalade would be an example ,they don't block the flow they desire the flow,bypassing the heater core but still allowing coolant through the heater supply and return hose. Super common factory GM valve less than 20.00.

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[edgephoto]

@josh454 Thanks for the feedback. Nice to know what happens in the end. Based on your pressures I knew your system was getting cold. You just needed the air to flow through it.