Question : Climate control vs fuel economy

[2.8-350TBI]

So, on a pretty recent trip to cali, at constant freeway speeds, I noticed that climate control has a WAY adverse effect on fuel economy. If I wing it, i'd say a 25% drop in fuel economy, everything but a/c works.

It seems logical for fuel economy to (somewhat) affect fuel economy, but this does NOT seem like a normal drop.

This is in my '89 2.8 5-speed blazer...
Can you guys tell me if this is normal?

[robertisaar]

25% drop seems wrong. a drop is normal though since it loads the engine more at the same speed.

[Weatheralls Auto]

If AC not working the only real load would be the blower motor which unless it shorting to ground (if that) would not even come close to a 25% drop in fuel Economy.

[2.8-350TBI]

Thats what I was thinkin but the truth is right there. I dont turn that crap on just to save gas. And I dont think the blower motor should put a big load on the engine, BUT every time I turn it up past 1 out of 4 speeds, the engine loads down.
IDK whats goin on, but its cold here in oregon, and gas isnt cheap.

[Azrael]

The A/C system usually only sucks up about 2-4 hp so the oil in the compressor might be done if it's never seen a service. Might be time for an A/C system purge and refill. The radiator fan is also supposed to be on when A/C is running. Maybe there's a possible short or drain there.

[2.8-350TBI]

The a/c system itself is okay, but its the a/c pump clutch that doesnt engage, thus no a/c.
I really need to figure this out.

[pmaniac69]

did you have it set to defrost? if so thats part of it cause the A/C compressor will turn off and on when set on defrost


but it still shouldn't be THAT much

[2.8-350TBI]

did you have it set to defrost? if so thats part of it cause the A/C compressor will turn off and on when set on defrost


but it still shouldn't be THAT much

The ac comp doesnt even engage, defrost or not. Any time climate control is on it drinks gas like a russian drinks vodka, or me with tequila for that matter lol.

Im takin it over to the college tomorrow and analyzing the whole system
Ill check the coolant itself, the amp draw from the fan, and you guys should give me suggestions on what else to check.

[pmaniac69]

alternator

[2.8-350TBI]

So, I brought out the VAT-40 and tested current draw at the alt...
Everything off, 3 amps current draw, when I turned the blower to full on the defrost with the heat all the way up, it was drawing 22 amps more! WTF!!!
So I turned my hid headlights on, and another 15 amps, geez, I have some serious issues goin on.

Any clues or ideas?

[2.8-350TBI]

Alternator pulled a steady 14 volts up to ~65 amps and 13 volts at ~85 amps

[robertisaar]

the headlight number sounds about right...

[pocket-rocket]

I honestly can't see the HVAC drawing more than 3-5 amps in all honesty. It's not like it has a heating element that runs on the electrical system or anything. That and an 89 Blazer would have vacuum controlled HVAC flaps, not the kind with the stepper/servo style like the newer vehicles. The alternator sounds up to snuff. Then again, when you said full defrost, was that with the rear window defroster on too? Those bad boys can draw some power.

[2.8-350TBI]

No rear defrost...

[Weatheralls Auto]

Back to post 3,
If the blower motor (which is the ONLY PART OF HVAC IN YOUR CASE) is loading the engine that much and if your fuel economy is dropping that much when it is on,
IT IS SHORTING TO GROUND, either internally or before.

Unplug blower and then turn on to high speeds, if it still loads engine you have a short before blower, if it does not then the blower is shorting internally.