This study investigated the effect of air-conditioning system on the tem-perature and speed of automobile engine before and after the air-conditioning system was put to use, while the vehicle was at static position. A 16-valve Nissan engine was used for this study, the engine was first run for 20 minutes before the data are collected. In the first case, the temperatures (℃) of the engine were taken in the interval of 10 minutes before and after the air-conditioning system is run and in the second case, the speeds of the engine were taken under the same conditions. The research hypothesis was formulated for 20 observations to argue that neither temperature nor speed of the engine changes when the air-conditioning system is put on and Paired t-Test statistics were used. The obtained result of t-statistics analysis for temperature and speed were -4.0329 and -5.51832 respectively. These results when compared to their critical values at 5 percent significant level, t-Statcritical < -1.73 for temperature and speed, were discovered to be at the rejection region which indicates that the null hypothesis (Ht0 and Hs0) in each case is rejected and accept that the air-conditioning system changes the temperature of the engine. Also, changes in speed requirements of the engine are not immediate and it could be as a result of an increase in fuel consump-tion due to more load on the engine. The regression correlation coefficients of 0.999996066 and 0.999653453 were obtained for the temperatures and speeds respectively with their R2 values, 0.999992132 and 0.999307027. The coefficients in the analysis were used to formulate the regression equations; T2 = 135.640 1.025t 0.496T1 and N2 = 634.005 3.824t 0.270N1 which can be used to forecast the temperatures and speeds of the engine during air-conditioning usage giving the initial parameters.
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