Temp gauge jumps when I switch on AC

[mosman58]

1976 2002 - aftermarket Dtech AC - works very well. once the car is up to temp - guage at mid way position - when I switch -on the AC it jumps straight to just below the red. Have checked earths etc. Car does not seem to be running hot - will check the top and bottom hose temperatures with a thermal gun.

 

Any thoughts? 

[visionaut]

coffee grounds - coffee =

[John76]

Check the threads on the temp sensor.  Needs a good ground path to the engine.

Did you check the alternator ground wire? Replace the wimpy OEM wire with a 10 AWG.

The A/C draws a big current, so check that the alternator is big enough (Amps) and the belt is not slipping.

Search the forum for "How to improve the instrument pod ground". 

[dlefebvre02]

Hey @mosman58!

 

First off, let me emphasize what @John76 and @visionaut said because they are more than completely correct. However, I am also a 1976 2002 owner, and in our specific scenario, my father and I pulled apart the dash and ran extra grounds only to find the problem not fixed at all (jumpy gauges with headlights/turn signals/any electrical load really). It turned out our main ground in the engine was filthy to the point where we could measure serious resistance across from it! After taking an appropriate cleaning brush to the contacts and reattaching with dielectric grease between them, our jumpy gauge problem went away entirely. I have attached a picture of the engine ground I am referencing, just in case I am giving the wrong visual.

 

Good luck with your problem!

 

(the ground I am talking about is right next to the brake fluid reservoir, ours had several other wire grounds stacked on top as well)

(this is from google, not a picture of my car)

Edited January 19, 2023 by dlefebvre02
grammer+photo reference

[John76]

I used a spare battery cable for an additional engine ground from the trans to the brake support structure (pic #1).

Also found that an extra ground wire on the fuel sender eliminated a jumpy fuel gauge when the right turn signal was used.

See green wire in pic #2.

Nothing wrong with being "well grounded" at all times. 

John

 

 

[Son of Marty]

+1 on Johns post, grounding the cluster won't work unless all the grounds are good, the interments are the most sensitive part of the system and telegraph all bad grounds in the system. Trisity is strange.

Edited January 19, 2023 by Son of Marty

[mosman58]

Thanks for the suggestions! The alternator is a Bosch AL41X which is rated at 65 amps.. swapped out the ground (earth with some coffee    ) to the alternator with 10 AWG. Will run it and see if its improved - cleaned battery ground. Will see if this improves things. 

[CaptainT]

The ground (earth) wire next to the fuel tank (not on the sender) invariably affects the instruments. Just make sure it has a good contact to metal.

 

Cheers 

TY

[mosman58]

Thanks for all the suggestions- checked and cleaned all the grounds - took the car for a drive and now when I switch on the AC the temp gauge just moves a little and goes back where it was. I believe this is to be expected as the AC draws a fair bit of current on startup.